In Vehicle Safety[1]

Crash Safety CentreSchoemakerstraat 97P.O. Box 60332600 JA DelftThe Netherlands

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TNO report

Literature survey on in-vehicle safety devices

Date May 9, 2003

Author(s) M.G.C. Rekveldt, MSc.K. Labibes, Ph.D.

Sponsor Swedisch National Road Administration (SNRA)SE-78187 BorlängeSweden

Approved by(Project Leader)

M.G.C. Rekveldt

Also seen by H.G. Mooi, Ph.D.Project code 009.01345Research period January - April 2003Number of pages 68Number of appendices A-CNumber of figures 30Number of tables 6

All rights reserved.No part of this publication may be reproduced and/or published by print, photoprint, microfilmor any other means without the previous written consent of TNO.

In case this report was drafted on instructions, the rights and obligations of contracting partiesare subject to either the Standard Conditions for Research Instructions given to TNO, or therelevant agreement concluded between the contracting parties. Submitting the report forinspection to parties who have a direct interest is permitted.

© 2003 TNO

TNO report 03.OR.BV.037.1/MRE | Literature survey ‘In-vehicle safety devices’ | 09 May 2003 2 / 68

Summary

This report presents a literature survey on in-vehicle safety devices. The study was splitinto two parts, from which the first part was focussed on restraint systems and thesecond on intelligent vehicle systems. This study aimed to give an overview ofpotentials for safety of current technologies available and trends in in-vehicle safetydevices.

The literature survey showed that the effectiveness of wearing seat belts in reducinginjury risk (up to 60%) is much higher than effectiveness of airbags only. Effectivenessof the seat belts in combination with airbags is 10-20% higher than effectiveness ofonly belts. Only very limited information on effectiveness of side- and curtain airbagswas available. New seat concepts were shown to claim a reduction of Whiplash injuryrisk and also a reduction of fatality risk. Side effects of restraints systems weredescribed, including the risks for out-of-position occupants. Current trends indicated theincreasing importance of the use of adaptive systems, in which occupant characteristicscan be taken into account to reach optimal restraint performance. These adaptivesystems include various sensors. Another important trend is to cover safety aspects forall occupants (front and rear occupants) and in all accident configurations, includingmultiple impacts.

Intelligent Vehicle Systems (IVS) can be used for comfort or/and for Safety. IVS forSafety were mentioned in this report as IVSS. Intelligence is already introduced innowadays cars like ABS (Anti locking Brake System) and more recently ESP(Electronic Stability Program). Estimations from in depth accidents analysis showedthat ESP could have reduced the likelihood or avoided the accident in 18% of all injuryaccidents and in 34% of fatal accidents. The new challenge is to introduce remotesensing for avoiding or mitigating a crash. ACC (Adaptive Cruise Control) is anexample of this technology, other systems will follow. An overview on IVS and moredetails on IVSS was provided in this literature survey including the estimated potentialof the systems to increase vehicle safety. This potential is obtained mainly fromsimulation and experts opinions and the obtained numbers have to be taken cautiously.It is agreed that IVSS tackle the first cause of accidents, which is driver errors.


Sammanfattning

Den här rapporten presenterar en litteraturöversikt över säkerhetsutrustning i fordon.Studien delades upp i två delar, där den första delen fokuserade på skyddssystem ochden andra på moderna så kallade Intelligent Vehicle Systems (IVS). Syftet med den härstudien var att ge en översikt av säkerhetspotentialen i aktuella tillgängliga tekniker ochtrender för säkerhetsanordningar i fordon.

Litteraturöversikten visade att säkerhetsbältets effektivitet att minska skaderisken (upptill 60%) är mycket högre än endast krockkuddens skadereducerande effekt.Säkerhetsbältets effekt tillsammans med krockkudden är 10-20% högre än endastsäkerhetsbältets. Endast begränsad information om sidokrockkuddars ochskyddsgardiners effektivitet finns idag tillgänglig. Nya bilstolar visade sig minskarisken för pisksnärtskador och resulterade även i en minskning av dödsriskerna.Säkerhetssystemens bieffekter beskrevs, inklusive riskerna för passagerare utansäkerhetsbälte. Utvecklingen visade den ökade betydelsen av användningen av adaptivasystem där passagerarnas egenskaper tas hänsyn till för att nå optimal säkerhet. Dessaadaptivasystem inkluderar olika sensorer. En annan viktig trend är att beaktasäkerhetsaspekterna för samtliga passagerare (passagerare fram och bak) och i samtligaolyckstyper.

IVS kan användas för komfort och/eller för säkerhet. IVS för säkerhet kallas i den härrapporten IVSS (Intelligent Vehicle Safety System). Intelligens finns redan i dagensbilar i och med ABS (Låsningsfria bromsar) och nyare ESP (antisladd-system).Beräkningar från olycksanalyser visar att ESP kunde ha minskat sannolikheten ellerundvikit olyckan i 18% av samtliga skadeolyckor och i 34% av dödsolyckorna. Den nyautmaningen är att presentera nya sensorer för att undvika eller minska våldet i enkollision. ACC (Adaptiva konstantfarthållare) är ett exempel på sådan teknologi. Andrasystem kommer inom kort. En översikt av IVS och mer information om IVSS ges i denhär litteraturöversikten, inklusive uppskattade systemmöjligheter föratt öka fordonssäkerheten. Potentialen beräknas i huvudsak från simuleringar ochexpertomdömen och de erhållna potentialerna måste tas med en nypa salt. Man äröverens om att IVSS kan adressera den största olycksorsaken, som är förarfel.


Contents

1 Introduction................................................................................................................... 6

2 Restraint systems........................................................................................................... 82.1 Safety belt systems.......................................................................................................... 92.1.1 Description of belt systems ............................................................................................. 92.1.2 Pretensioners ................................................................................................................. 102.1.3 Load limiter................................................................................................................... 102.1.4 Potential of belts to increase safety ............................................................................... 112.2 Seats .............................................................................................................................. 142.2.1 Seat design aspects........................................................................................................ 142.2.2 Potential of seats to increase safety............................................................................... 162.3 Airbags .......................................................................................................................... 182.3.1 Description of airbag systems ....................................................................................... 182.3.2 Frontal airbags............................................................................................................... 192.3.3 Potential of frontal airbags to increase safety................................................................ 202.3.4 Side airbags for chest and head & curtain airbags ....................................................... 212.3.5 Potential of side airbags to improve safety.................................................................... 222.3.6 Special head protection airbags and curtain airbags...................................................... 222.3.7 Potential of head airbags and curtain airbags to increase safety ................................... 242.3.8 Other airbags ................................................................................................................. 242.4 Interior panels and retractable steering columns ........................................................... 252.5 Integration of safety concepts ....................................................................................... 27

3 Side effects of restraint systems ................................................................................. 313.1 Injuries caused by belts ................................................................................................. 313.2 Injuries caused by airbags ............................................................................................. 313.3 Out-of-position (OOP) .................................................................................................. 323.4 Effects of restraint systems on elderly ......................................................................... 343.5 Effects of restraint systems on small children and child restraints................................ 343.6 Effect of occupant characteristics on injury risk ........................................................... 35

4 Trends in restraint systems ........................................................................................ 364.1 General trends ............................................................................................................... 364.2 Trends in tools for restraint system development.......................................................... 364.3 Trends in safety ............................................................................................................. 374.3.1 Investigation of multiple impacts .................................................................................. 374.3.2 Safety of rear occupants ................................................................................................ 384.4 Trends in belt design ..................................................................................................... 384.4.1 Four point belt ............................................................................................................... 384.4.2 New belt concept – inflatable belt................................................................................. 394.4.3 New belt pretensioners.................................................................................................. 394.5 Trends in airbags ........................................................................................................... 404.5.1 Airbag design ................................................................................................................ 404.5.2 Inflator technology ........................................................................................................ 404.6 Sensors .......................................................................................................................... 404.7 Potential effectiveness of adaptive restraint systems .................................................... 42


5 Intelligent Vehicle Systems (IVS)............................................................................... 435.1 IVS in vehicle safety applications ................................................................................. 435.1.1 ABS Anti locking Brake System or Antilock Brake System ....................................... 445.1.2 ASR Acceleration Slip Regulation .............................................................................. 445.1.3 ESP Electronic Stability Program .............................................................................. 445.1.4 Adaptive Cruise Control (ACC).................................................................................... 455.2 IVS potential to integrate Passive safety and active safety ........................................... 465.3 Pre-Crash Sensing (PCS) systems................................................................................. 475.3.1 Example project: Chameleon t[29] ............................................................................... 485.3.2 Pre-crash sensing potential and limitations to increase safety ...................................... 495.4 Trends in IVS for safety................................................................................................ 505.5 Discussion ..................................................................................................................... 52

6 Remote sensor technology .......................................................................................... 546.1 Ultrasonic sensors ......................................................................................................... 546.2 Infrared sensors ............................................................................................................. 546.3 Radar ............................................................................................................................. 556.4 Lidar .............................................................................................................................. 576.5 Artificial vision : (video pattern recognition)................................................................ 576.6 Data sensor fusion ......................................................................................................... 58

7 Conclusions .................................................................................................................. 597.1 Restraint systems........................................................................................................... 597.2 Intelligent Vehicle Systems........................................................................................... 59

8 References .................................................................................................................... 61

AppendicesA GlossaryB List of relevant IVS related EC projectsC Overview actual regulations and consumer tests


1 Introduction

At the end of December 2002, Swedish National Road Administration inviteduniversities, polytechnics and research institutes around the world to carry out literaturestudies on several subjects related to road safety including the subject ‘in-vehicle safetydevices’. The exact formulation of the call was:

‘The effect and potential in using different modern safety systems in vehicles. Whatneeds to be improved and developed? Examples of systems to describe are: airbags,side-impact airbags for chest and head, modern safety belt system (safety beltpretensioner, force limiter etc). What potential lies in other in-vehicle systems, such asintelligent cruise control, ESP, ABS brakes and traction control?’

The successful submission of TNO included:

The study on in-vehicle safety devices will be split into two parts. In the first part, adescription will be given of current restraint systems in cars, developed for frontal, sideand rollover impact situations. Different types of airbags (driver & passenger frontal,side airbags, knee airbags, curtain airbags) and belts (including pre-tensioner,retractor etc.) will be considered. Attention will also be paid to the possible negativeeffects of these restraint systems. For example, out-of-position situations in which anoccupant is interacting with a deploying airbag will be taken into account.

The second part of the in-vehicle safety study will focus more on active safety includinguse of anticipatory sensors to make restraint systems more efficient. An inventory ofcurrent and future active systems will be made as well as an overview of the mostrelevant components for such systems. Apart from technical aspects legal factors andother deployment related aspects will be considered as well. The basis for this work willbe studies into sensor technologies and sensor algorithms performed by TNO in 2001.These studies will be extended with the latest developments for sensors as well asactuators.

This report presents the results of the literature survey. Sources used in the literaturesurvey included:

− Proceedings of conferences like STAPP, IRCOBI, AIRBAG 2002, SAE− Scientific journals− SAE global mobility database− NHTSA website, Transport Canada website− Studies into sensor technologies and sensor algorithms by TNO in 2001− Websites of restraint system manufacturers like Breed, TRW, Autoliv, sensor

manufacturers like Bosch, Siemens

This report can be divided in two main subjects: ‘Restraint Systems’ and ‘IntelligentVehicle Systems’. The second part of the in-vehicle safety study will focus more on thenew trends including the link between active and passive safety via the use ofanticipatory sensors to make restraint systems more efficient. An inventory of currentand future active systems will be made as well as an overview of the most relevantcomponents for such systems. Apart from technical aspects legal factors and otherdeployment related aspects will be considered as well. The basis for this work will bestudies into sensor technologies and sensor algorithms performed by TNO in 2001.


These studies will be extended with the latest developments for sensors as well asactuators.

In this study, the term Abbreviated Injury Scale (AIS) is used for injury assessment.The AIS, first developed by the Association for the Advancement of AutomotiveMedicine in 1971, is a consensus-derived, anatomically based system that ranksindividual injuries by body region on a scale of 1 to 6 (1=minor, 2=moderate,3=serious, 4=severe, 5=critical, and 6=maximum/currently untreatable). The AIS isintended as a measure of the severity of the injury itself and not as a measure ofimpairments or disabilities that may result from the injury. It does not assess thecombined effects of multiple injuries to a patient. The AIS was revised and updatedseveral times, with the most recent revision in 1990. In this report, the AIS level (i.e.,AIS of 2 or more) refers to the maximum AIS level for that injury suffered by a vehicleoccupant. The MAIS refers to the maximum AIS level (the most severe injury) for allinjuries.

This report aims to give an overview of restraint systems and technologies available inthe current fleet and potentials for safety. In more detail, the content of this reportincludes:

− Chapter 2: Restraint systemsThis chapter will describe current systems and will indicate its potential. Alsoexpected effects of integrated safety systems is discussed.

− Chapter 3: Current drawbacks of restraint systemsAlthough restraint systems have positive effects (will be shown in chapter 2) alsoless positive second order effects are observed. This chapter gives an overview of theproblems.

− Chapter 4: Trends in restraint systemsChapter 4 describes the trends observed from literature. This also connects the firstpart of the literature survey with the second part since future trends in restraintsystems include the use of adaptive, smart restraint systems.

− Chapter 5: Intelligent vehicle systems (IVS)Chapter 5 describes the new trends in vehicles like ACC emphasising the potential ofIntelligent Vehicle Systems for enhancing safety.

− Chapter 6: Remote sensor technologyIVS are based on remote sensors. These sensors will be increasingly implemented infuture vehicles. A chapter is dedicated to this technology.

− Chapter 7: ConclusionsThis chapter shortly summarises the most important findings from this literaturesurvey.

The glossary describing all abbreviations used in this report is given in Appendix A. Alist of European projects in the field of IVS for safety is given in Appendix B. Someinformation on regulations involving restraint systems or intelligent vehicle systems isprovided in Appendix C.


2 Restraint systems

Restraint systems are systems that restraint the occupant and protect the occupant incase of crash. The introduction of restraints systems like airbags, seatbelts and energyabsorbing interiors, considerably reduced the number of fatalities and casualties world-wide. The number of fatalities in road accidents in Europe, USA, Canada, Japan, Korea,Australia and New Zealand for the last decades is shown in Figure 1 [95]. Despite of theincreasing number of vehicles on the roads, the number of fatalities is still decreasing.

100000

120000

140000

160000

180000

200000

220000

1960 1965 1970 1975 1980 1985 1990 1995 2000 2005

fatalities world wide

Figure 1- Fatalities in road accidents ‘world wide’ from 1965 until 2000, data from [95]

However, in the European Union, still approximately 40.000 people are killed in roadtraffic accidents and 1.5 millions casualties are reported each year. Social costs relatedto these deaths and casualties are estimated to be over 160 billion Euro [60], [144].Decreasing the fatalities and injuries would reduce these costs enormously. TheEuropean Union set an ambitious goal to halve the number of people killed annually by2010 [144]. The EU intends to contribute to this goal with actions on two levels: 1.Harmonisation of penalties and 2. Promotion of new technologies to improve roadsafety.

The European guideline for cost effectiveness of safety measures is that a measure iscost effective if one fatality (and a particular number of (severe) injured people andmaterial damage) is prevented at maximum cost of 1 million Euro [94]. This guidelineis based on accident statistics for the complete European Union.

Nowadays, cars are equipped with several restraint systems to prevent the occupantfrom being injured during a crash. Children require special restraint systems and forprotection of these child occupants, child restraint systems are used in conjunction withadults’ restraint systems. This chapter describes the current (adults’) restraint systemsand its benefits. Limitations or drawbacks of current restraint systems are given in thenext chapter.


2.1 Safety belt systems

2.1.1 Description of belt systemsInitially the only goal of seatbelts was to prevent total ejection of occupants from a carduring a crash [23]. This was achieved with a single lap belt, introduced in car racingjust after 1900. The next additional goal of seatbelts was to protect the occupants fromviolent impacts against interior structures. Adding a shoulder belt to the lap beltcontributed to achieve this second goal. After the Second World War, different types ofbelts were introduced in private cars (for example Volvo and Saab in 1956). For wellfunctioning of the belt, the geometry of the belt and hence the location of the anchoragepoints was shown to be important. The last decades, seat belts were enhanced byadditional features like force limiters and pretensioners, see section 2.1.2 and 2.1.3.

Current conventional seat belt systems are the three-point belts, in which the shoulderbelt upper anchor is mounted to the vehicle body (B-pillar), see Figure 2.

Figure 2 – Conventional three- point belt system [96]

Properly fastened safety belts distribute the forces of rapid deceleration over larger andstronger parts of the person’s body like chest, hips and shoulders. The safety beltstretches slightly to slow the body down and to increase its stopping distance. Thelocation of the belt at the occupant’s body during a crash is essential for properfunctioning of the belt. For example, if the lap belt is located too high, the occupant canslip under a loosely tightened seat belt, which is called ‘sub-marining’. More and more,belt systems are integrated in the seats; see section 2.2.

Seat belts are multi-functional, e.g. work in all different types of accidents like frontal,side, rear end and rollover. Current belt systems include [24]• Retractor; a spool, which is attached to one end of the webbing. Inside the retractor, a

spring applies a rotation force to the spool to rotate the spool so it winds up any loosewebbing, see Figure 3.

• Buckle, which must be able to withstand high forces as well as open easily even uponheavy loading,

• Height adjuster to achieve correct belt geometry (manual or automatic),


• Load limiter integrated in the retractor to keep the maximum belt force at a pre-defined, controlled level,

• Pretensioner to tighten the belt during the very first fractions of a crash.

Figure 3 – Left panel: drawing of retractor, right panel, drawing of pretensioner [97]

Some details on pretensioners and load limiters are given in the next sub-sections.

2.1.2 PretensionersPretensioners were introduced in 1984 [25] and remove slack from the belt (tighten thebelt) early in the crash event using a small pyrotechnic charge to push the occupants totheir seat during the crash. Modern pretensioners typically use the same sensor as theairbag. Pretensioners can tighten the belt up to 15 cm by pulling the seatbelt buckletowards the floor (Buckle pretensioner) or by operating the retractor (Roto pretensioner)[24].

The potential for dual belt pretension was investigated by Renault [20]. Accidentanalysis of LAB data in this study showed improvements for the protection of the upperbody of belted occupants as a result of improved restraint systems (load limited belts &airbags), and reduction of passenger compartment deformation. However, leg protectionof front seat occupants still could be improved and therefore, a dual belt system isproposed, consisting of a buckle lap-belt pretensioner and an outer lap-belt pretensioner.The buckle pretensioner is fired first, a few ms later the outer belt pretensioner is firedwith a typical time interval of 10 ms in an offset frontal crash situation. Benefit of thedual belt pretension system over single pretension in terms of reduced pelvisacceleration and velocity (peak velocity from 3.5 m/s to 2 m/s) was presented.

2.1.3 Load limiterLoad limiters were introduced in 1995 [24] and keep the belt force at predefined,controlled level. A mechanism in the retractor allows webbing to be pulled out slightlywhen belt loads become too high. Normally a pre-set limit of 4 kN is used.

There are several technical solutions to achieve the load limiting. A typical solution isprovided by a bar holding the spindle with the webbing within the retractor, see Figure4. If the force from the webbing exceeds the limit, the end of the bar turns and reducesthe load on the occupant’s chest.


Figure 4 – Load limiter [24]

In 2000, Autoliv introduced 2-stage load limiters to keep the load on the occupant’schest constant during the whole crash [24]. During a crash, initially the occupant is onlyrestraint by the belt, which demands a relatively high belt force. As soon as theoccupant moves forward into the airbag, the belt’s load limit is reduced since the airbagtakes over part of the occupant’s load.

2.1.4 Potential of belts to increase safetyIn several studies, modern seat belts have been shown to reduce injury risk in frontalcrashes with about 50% [61]. A recent study published in the Journal of AccidentAnalysis and Prevention estimated that seat belt use by front-seat passengers reducedthe risk of death in a crash even by about 61% [139]. However, it is also known that inabout 50% of severe crashes, seat belts are not worn [47]. The major excuse of non-beltusage is discomfort and inconvenience in using the belt.

Comfort and usability was, amongst others, studied by Delphi Automotive Systems [48]by means of a questionnaire study (194 respondents). The most significant problemswere found as belt trapping in the door, awkward negotiating with clothes, belt twisting,belts locking up and difficulty to locate the buckle.

A more extensive study about non-user’s reasons for not wearing the seat belt wasperformed by VTI [136]. Drivers not using the seat belt (435 drivers) were interviewedand, amongst others, asked for the reason not to wear the seatbelt. Results for thisparticular question are summarised in Table 1. From this study it was concluded that thebasic attitude of these drivers to seat belts was in most cases positive, since the mainreasons not to wear the seat belt were not very principle.

The institute for road safety research in the Netherlands (SWOV) published the reasonsnot to wear the seat belt amongst Dutch drivers [137], see Table 2. Main reason for theDutch drivers in 2000 not to wear a belt is simply ‘forgot’, indicating that seat wearreminder systems could reduce the amount of non-wearing seat belt drivers.


Table 1: Results Swedish interview: ‘why did you not use the seat belt on this occasion?[136]

Reason %

Only a short trip 34,5

Carelessness 32,9

Forgot, forgetfulness 23,0

Stressed, in a hurry 10,6

Professional driving, job 10,6

Had no time to put it on yet 4,5

Habit, “bad habit” 4,5

Uncomfortable to wear 3,4

Do not use as a matter of principle 3,4

Feel locked in 2,8

Only urban trip 2,3

Frequent stops 1,8

Cumbersome to put on 1,6

Belt is / can be dangerous 1,4

Belt is not necessary 0,9

Restricts reach 0,9

Don’t know, no answer 0.9

Drives (drove) slowly 0,7

Avoids accidents 0,7

Interference with clothes 0,7

Tired 0,7

Usually “always” wears belt 0,7 Bold lines represent the ‘hard resistance’ group.

Table 2: Results Dutch study: reasons not to wear the belt [137]

Reason % 1998 % 2000

Forgot 31 46

Uncomfortable 31 20

Unnecessary 9 10

Dangerous 3 3

Seat belt wear percentage for several countries around the world is presented in Figure5 [98]. Dependent on the road type, different improvement of sear wear rates ispossible.


Figure 5 – Seat belt wearing rates for car drivers in 2000 [98]

To increase the seat belt wear percentage, seat belt reminder systems are currently onthe market as an addition to the ‘conventional belt systems’ described in section 2.1.EEVC working group 16, Advanced Frontal Crash Protection, studied the potential oftechnical means to increase the use of seat belts in cars and proposed specifications forsuch systems with special interest for reminder systems [47]. One of therecommendations of the EEVC working group for seat belt reminder systems was that aseat belt reminder system should not affect drive-ability of the vehicle and shouldconsist of a progressive reminder system with audible and visual signals. Seat usedetection was recommended also for other seats than the driver seat with a lower limitof a 5th % female to avoid false signals by small luggage or ISOFIX child restraintsystems. It was also recommended that the seat belt reminder systems should havedisconnection possibilities. Currently seat belt reminder systems are taken into accountwith EuroNCAP tests on voluntary base [appendix C.4].

Effectiveness of Ford’s belt reminder system in increasing seat belt use in the US wasinvestigated by IIHS [138]. An observational survey was conducted to compare driverbelt use in 2000-2002 models with belt reminders with belt use in 1998-2001 modelswithout reminders. The overall use rates were estimated as 71% for drivers of vehicleswithout belt reminders and 76% for drivers of vehicles with reminders. This increase inbelt wearing was statistically significant.

Evans summarised technical evidence for the effectiveness of safety belts in [117].From impact biomechanics it is known that belts prevent the occupant from hitting theinterior of the vehicle, or reduce the severity of such impact. Forces on the occupant arespread over a larger body area and the deceleration is spread over a longer time.Besides, belts prevent ejection from the vehicle. The belt effectiveness at reducingdriver fatality risk, averaged for all types of crashes, is in the range 38% to 46%. In caseof rollover, the belt is 80% effective in preventing driver fatalities if rollover is the firstevent. Also the effect of the belt wearing law in the UK was described: a 23% decreaseof fatalities was reported in the 11 months after the law [146].


Reduced fatalities related to rear seat shoulder belts were reported in [143]. It wasshown that death rates in cars equipped with shoulder belts in rear seats weresubstantially lower that in cars equipped with lap belts at prevalent use rates. Therefore,it was concluded that shoulder belts reduce the risk of death compared to lap beltswithout shoulder belts.

Rollover restraint performance with and without seat belt pretensioner was investigatedin [120]. Research tests according to a modified FMVSS 208 dolly rollover test wereconducted in which driver’s and front seated passenger’s restraint performance wereanalysed. The rollover test method resulted in unrepeatable vehicle dynamics, butnevertheless, proper restraint performance was shown. It was concluded that themaximum occupant injury values did not indicate any improved protection for the testswith pretensioners activated, compared to the tests without pretensioners. It was notedthat the pretensioners used in this study were not designed for rollover application.

2.2 Seats

2.2.1 Seat design aspectsIn the past, the seats were particularly important as far as comfort was concerned. Seatdevelopment was mainly comfort focussed. Besides importance in case of rear and sideimpact, also in frontal impact, the seat plays an important role in occupant prevention[1]. In particular anti-submarining pans are used to control the pelvis motion in the seatand to prevent the occupant from submarining under the lap belt. Whereas these devicesused to consist of metal pressings that absorb impact energy by controlled deformation,nowadays a more variable anti-submarining device, an airbag within the seat, wasintroduced by Autoliv [22].

For side impact protection, seats have an important function in energy absorption.Geometry and material of the side bolsters influence seat–occupant interaction in acrash event. Also the strength of the seat adjustment is important for side impactprotection.

During rear impact, the occupant moves rearward relative to the vehicle and the seatback provides the primary ‘restraint system’ for the occupant. Therefore seat designinfluences the injury potential. The influence of seat foam and geometrical properties ona dummy’s kinematic response to rear impacts was studied in [99]. It was concludedthat for the three seats being subject of investigation in this study, the geometricalproperties of the head restraint considerably more influence the occupant kinematicsand thus whiplash associated disorder potential than seat foam properties. Thisconclusion confirms other (previous) studies in which reduced distance between headrestraint and the back of the head and increased height of the head restraint were shownto be important for injury reduction [100], [101], [102]. For the influence of seat foamproperties, contradictory conclusions were reported and the influence of the materialproperties compared to the geometrical characteristics was limited.

A new generation of yielding seats was described by Viano, [130], see also Figure 6.The compliance of the high retention (HR) seat is an important factor in the reduction ofwhiplash risks, see section 2.2.2.


Figure 6 – New generation of yielding seats, example of high retention seat [130].

Also Autoliv introduced an Anti-Whiplash Seat (AWS) for front seat occupants, whichhas a yieldable backrest that will be tilted in a controlled way in a rear-end collision.The aim is to absorb energy and reduce the forward rebound of the occupant [24].

Volvo developed and published the WHIPS seat concept [141], [142]. The WHIPSproject followed the whole chain, from accident research and biomechanicalknowledge, towards interpretation of the knowledge, condensed into guidelines andrequirements, resulting in seat development and validation. This holistic approach wasneeded because the injury mechanisms for whiplash are still not fully clarified. Thefollowing guidelines for dealing with the Whiplash problem were identified:1. Reduce occupant acceleration2. Minimise the relative movement between adjacent vertebrae in the occipital joint3. Minimise the forward rebound into the seat belt.The recliner of WHIPS was designed to give a controlled rearward motion of thebackrest in a rear-end impact, thereby, improving the closeness to the occupant’s headand back, absorbing energy and reducing the occupant’s forward rebound.

A Self-Aligning Head Restraint (SAHR), also called Saab-Active Head Restraint) wasdesigned to move upward and forward by occupant motion in a rear crash, providingearlier neck support, even when the head restraint is positioned low [147].

Figure 7- SAHR mechanism [147].


SAHR uses the momentum of the occupant pressing into the seatback in a rear crash toraise and move the restraint forward, providing earlier head neck support and loweringloads causing neck extension. Potentials are described in section 2.2.2.

A Seat Integrated Restraint (SIR) system has the shoulder belt upper anchor mounted onthe top of the seat back frame, see Figure 8. SIR systems provide better belt fit, betterbelt access and greater comfort to the occupants and therefore add to customersatisfaction.

Figure 8 – Examples of seat integrated belt system, left panel [24], right panel [10].

Design targets for seat integrated restraint systems for optimal occupant protection wereamongst others studied by Ford Motor Company [10]. Also in case of a seat-integrated-restraint (SIR), the stiffness of the seat and the floor underneath the seat play asignificant role in protection for frontal impact situations. Working of a prototype SIRsystem, equipped with belt pretensioner and load limiting retractor and additional dualstage driver airbags, was investigated by computer simulation with the simulationpackage MADYMO [10]. Seat excursion, referred to as the total forward displacementof the shoulder belt upper anchor relative to the vehicle, was shown to be an importantparameter to optimise the SIR system and should be limited. Proper structural design ofthe seat, seat attachment and structural design of the floor were indicated as the keyparameters to influence seat excursion. When choosing seat excursion as a designparameter, it is important to make a distinction between the contribution to excursion ofthe seat and its underlying structure. Since seat excursion is also dependent on vehiclepulse and pitch, the design targets of seat/floor stiffness can not be generic for all typesof vehicles. Proper selection of belt retractor, airbag vent size and dual stage inflator’slag time contribute to lower injury values.

2.2.2 Potential of seats to increase safetyThe potential of seats to increase occupant safety lie both in the head restraint and theseat structure itself, although for the latter different opinions were found in literature.Better head restraint systems could contribute to reduction of the neck injuries in rearimpacts [134]. Yearly, more than one million European citizens suffer neck injuriesfrom car collisions. About 50% of these neck injuries occur in rear-end impacts. The 5th

framework European project WHIPLASH-2 [134] aims to reduce the risk and societalcosts of low-severity neck injuries in car collisions by at least 40%, by means of theintroduction of safer vehicle designs.


Identification of issues relevant to regulation in the US, design and effectiveness ofhead restraints was given by NHTSA [127]. In 1982, effectiveness of integral restraints(seat with non-adjustable ‘integrated’ head restraint) was estimated about 17% and foradjustable head restraints about 10%. This difference was caused by the fact thatadjustable restraints were not always used properly. Often, adjustable head restraintswere left in lowest position.

Only limited scientific information is available on claims of injury risk reduction in rearimpact due to new seat concepts. Volvo developed and published the WHIPS seatconcept [141], [142], see section 2.2.1. Results of sled tests suggested considerablepotential for improved neck injury protection in rear-end impacts. No concrete numberswere given. Effectiveness of a Self-Aligning Head Restraint (SAHR) in preventingWhiplash was investigated in [147]. The study evaluated the field performance ofSAHR by means of questionnaire mailing to the occupants involved in rear crashes,phone interviews and reviewing of insurance and medical records. 177 cases, 85 withstandard head restraint and 92 with SAHR were included. It was concluded that SAHRreduced whiplash injury risks by 75±11%, from an 18±5% occurrence out of 85occupants with standard head restraints to 4±3% occurrence out of 92 occupants withSAHR.

Some indication on positive effects of the correct use of head restraints were found in[125], in which soft tissue neck injuries after rear-end collisions were reported. 245accident cases from the GDV 1990 database (Germany) were analysed with thefollowing characteristics: rear-end collision, single impact, claimed cervical spine injuryand good documentation. The cases were divided into 4 groups; lowest fixation, highestfixation, medium fixation (in between low & high) and no head restraint. It wasconcluded that it is better to have no head restraint than having one that is too lowadjusted. A high head restraint position was found to reduce the cervical spine injuryrisk.

The risk of whiplash injury in the rear seat compared to the front seat in rear impactswas investigated by Folksam Research et al, [135]. In total 195 cases with both front-and rear seat passengers in the struck car were analysed with at least one occupant whosustained permanent disability. It was concluded that there was a significantly higherdisability risk for the female rear seat occupant compared to the mail driver. Also higherrisks for the female rear-seat occupant were found compared to the female front-seatpassengers. The risk of permanent disability was four times higher for females in therear seat, compared to males in the rear seat. For drivers, the risk of permanentdisability was three times higher for female drivers than for male drivers.

Relationships between passenger car seat back strength and occupant injury severity inrear end collisions were, amongst others, studied in [126]. Several seats with differentseat back stiffness and geometry were evaluated in dynamic Hyge rear impact sled tests.Results of these tests indicated no consistent advantage of stiffer seats over yieldingseats for the complete range of speeds tested. Moreover, indications were found thatstiffer seats could increase the incidence of neck injuries in real world. The mostsensitive response to seat design and crash severity was the lower neck extensionmoment.The effect of stiff and yielding seats and energy transfer to an occupant in rear crasheswas also described in [130]. This (more recent) study showed more clearly benefits of ayielding seat back over a stiff seat on occupant dynamics in rear crashes. The yielding


seat back developed about 15% lower forces on the occupant and a more gradualforward acceleration of the occupant was observed.

Effectiveness of High-Retention (HR) seats (see also Figure 6) in preventing fatalitywas studied in [140]. After 5 years of phase-in of HR seats, accident analysis withFARS data was undertaken to determine the initial field performance of the HR seats inpreventing fatalities. The fatal crash information consisted of samples from FARS from1991-2000. FARS data analysis showed 50% reduction of the risk of driver fatalities insingle-vehicle rear crashes and 59% reduction of the risk of front occupant fatalitiesusing the HR seat. For two vehicle rear impact crashes, the HR seat reduced the risk ofdriver fatality by 54% and the front occupant fatality risk by 35%. It was noted thatmore field data is needed to increase the confidence in the results. However, the initialtrends showed that high-retention seats are effective in reducing the risk of fatal injuryin single vehicle and light vehicle-to-vehicle rear impacts.

2.3 Airbags

2.3.1 Description of airbag systemsAirbags are inflatable restraints, which are connected to sensors that detect certainsudden deceleration. Airbags were introduced in 1973 by General Motors [25]. Ageneral description of airbag working principles was, amongst others, found in [2] and[3]. In case of activation of the airbag, the sensor ignites a chemical propellant bymeans of an electrical signal. The propellant (inflator) produces gas that inflates theairbag. Enough gas is needed to prevent the airbag from “bottoming out” against thevehicle interior when an occupant is hitting the airbag. Therefore, the airbag pressurehas to be carefully controlled by vents and outflow through the airbag fabric(permeability of the fabric material). The airbag fabric material is nylon.

Airbags systems consist of an electronic control unit and the airbag module itself. Theelectronic control unit is usually located in the middle of the car or mounted in thesteering wheel (in case of a driver airbag). The sensor that sends this information into amicroprocessor continuously monitors the acceleration and deceleration of the vehicle.In the microprocessor, the crash algorithm (different for each specific car model) isstored and continuously compared to the sensor signal. If the microprocessor recognisesthe specific crash pulse, an electrical signal is given and the airbags are fired.

Different types of inflators are used. Single stage inflators fill air bags with the samelevel of power in all crashes, regardless of whether the crash is a relatively low or high-speed crash. Multi-stage inflators (mostly dual stage) consist of multi (two) independentinflators and enable a more controlled airbag deployment. In case of a low severitycrash, only the first stage is fired, whereas in case of a high severity crash, both stagesare fired. High severity crashes require higher airbag pressure to prevent the occupantfrom hitting the vehicle interior.

The main challenge for airbag systems is that they have to satisfy all protectionrequirements in different vehicle crash scenarios and for different occupant sizes. Forboth high-severity crashes (fast airbag deployment demanded) and low severity crashes(gentle airbag deployment demanded), the occupant should be optimally protected andhard contact of the occupant with the car interior should be avoided. Different types ofairbags (frontal, side etc) with different deployment times are developed for the


different types of crashes. The following subsections will describe the different types ofairbags an their effects in more detail.

2.3.2 Frontal airbagsFrontal airbags protect the head and the upper body of the occupant in frontal crashes,see Figure 9.

Figure 9 - 5th percentile dummy in frontal crash test: scenario without an airbag (left), scenario with anairbag(right) [148].

The main function of frontal airbags is to prevent hard contact between the occupantand the steering column / interior panel / windshield during a crash. The airbag shouldtherefore be properly positioned between the occupant and the car interior. Typical sizesof frontal airbags vary for cars in different countries, depending on seat belt wearobligation. In the US, wearing belts is not compulsory and a larger volume within thecar has to be filled by the airbag. Typical airbag sizes for the US are 65-80 litre fordriver airbags (fitted in the steering wheel) and 150-160 litre for passenger airbags(fitted in the interior panel at passenger side). For Europe and Japan, where wearingbelts is compulsory, smaller airbags are appropriate (35-60 litre for driver airbags and80-120 litre for passenger airbags) [4]. Airbag deployment takes about 30-50 ms.

A smart driver airbag concept called ‘ring-airbag’ was presented by Audi in 2002 [15],see Figure 10.

Figure 10 – Ring-airbag concept [15].

This ‘ring-airbag’ was developed to meet all requirements of consumer protection andlegislation taking into account sophisticated styling freedom. The new Audi A8contains a fixed airbag module centre together with a ring-airbag.


On the one hand, airbags have to be positioned in time and should have enough energyabsorbing capabilities to protect the occupant. On the other hand, occupants in out-of-position require limited inflation pulse through the airbag. This can be reached forexample by avoiding contact between module flap and occupant, improved folding,radial deployment, or controlled unfolding. The smart ring-airbag concept includes allthese measures. Tests showed that the ring-airbag fulfils all safety requirements andimproves results for ‘low risk deployment’ FMVSS 208 tests (for information onfmvss208, see section C.2.2).

2.3.3 Potential of frontal airbags to increase safetyFrontal airbags have been shown to be highly effective in saving lives. Effectiveness ofairbags in preventing fatalities was already studied in 1990 by Evans [75]. It wasassumed that frontal airbags protect only in frontal or near frontal crashes and do notaffect the ejection probability. Airbag effectiveness in preventing fatalities wasestimated as 18±4% for drivers and 13±4% for passengers. Lap/shoulder belted driverswho stop wearing belts because of airbag presence would increase their fatality risk byover 40%.

Frontal airbag benefits/dis-benefits in European vehicles were evaluated with acombined statistical and case study approach by VSRC Loughborough University [40].The statistical evaluation was based on accident cases from 1996-2001, collected withinthe UK Co-operative Crash Injury Study. In total about 2300 cases were evaluated,divided in equipped, non-equipped and belted/unbelted. Differences in car performancedue to improved seat belt systems and structural changes in newer cars were taken intoaccount. The maximum AIS (MAIS) of each occupant was used to compare overallinjury severity between the non-equipped and the equipped samples for the belted andunbelted driver groups. For the belted drivers, 32% of the non-equipped drivers hadMAIS ≥2, for equipped drivers only 24% had a MAIS ≥2. For the unbelted group, thedifference was much smaller (40% non-equipped to 37% equipped). Only the reductionfor the belted group was statistically significant. For head injury, less severe injuries arereported for equipped vehicles with respect to non-equipped vehicles for both beltedand unbelted drivers. Previous studies identified an increased injury risk for headinjuries for short stature drivers but this trend was confirmed in this study for non-equipped cars only. Crash circumstances in which AIS ≥ 2 head injury occurred inairbag equipped vehicles included high equivalent test speed (ETS), under-run, andinteraction with heavier vehicles or poles. It was suggested that airbag systems mighthave difficulty in sensing impacts to narrow objects. A small (statistically in-significant) increase in the rate of neck strain (AIS 1 injury) was observed for equippedbelted drivers with respect to non equipped belted drivers and a decrease for unbelteddrivers. For thoracic injury, reduced injuries in case of equipped cars were observed forboth belted and unbelted drivers. Statistically no increase was found in the rate of burns,abrasions or contusions to face or neck for belted and unbelted drivers in airbagequipped vehicles, but some examples were reported in the case review (see section 3.2on injuries). For lower arms and hands significant increases of rate of abrasions, burnsand contusions were found for belted drivers in equipped cars. However, these were notsevere injuries (AIS 1). Generally it was concluded that airbags are more effective inpreventing injury when worn in conjunction with the seatbelt, since absence of the seatbelt allows forward excursion into the airbag deployment zone.

Airbag benefits were confirmed also by a recent study of the Institute for Vehicle Safetyin Germany, GDV [46]. About 700 cases involving airbag-equipped cars, from which


92% since 1997, were studied. Not only for the driver, but also for the front seatpassenger the study confirmed major safety benefits of airbags. The proportion ofsevere and fatal injuries both to driver and front passenger is about 20% lower thanwithout airbags.

With the first generation airbags unexpected fatalities were reported, particularly in lowspeed crashes [2]. As a result, depowered airbags (less power when inflating) weredeveloped from 1997 on. The performance of these depowered airbags was investigatedby William Lehman Injury Research Center [5]. In this study, it is concluded that theperformance of the depowered airbags has been very good. High-speed protection atcrash severities > 40 mph has been observed for both restrained and unrestrainedoccupants, despite of the depowered airbags.

2.3.4 Side airbags for chest and head & curtain airbagsSide impacts represent the second greatest cause of fatalities in passenger car incidents[62]. After the standardisation of frontal airbags, vehicle manufacturers starteddeveloping dynamically deploying upper-interior head and thorax protection systems(introduction started in 1994). These systems provide additional occupant protection ofhead, neck and thorax area and also prevent the occupant being ejected from the vehicleduring lateral crashes. Development of side-airbags is more complex than developmentof frontal airbags since in frontal impacts, much energy is absorbed by bumper, hoodand engine, whereas in side-impact, the occupant is much closer to the incoming vehicleand only the door and some additional space is in between [16]. Therefore for side-airbags, typical inflating times are 7-15 ms, which is much lower than for frontalairbags [62].

The mounting location of side airbags is different for different types of cars. Installationin the seat back has the advantage that passengers of all sizes are protected regardless ofseat position. Installation in the door has the advantage that within the door, there isenough space to enable acceptable coverage.

Autoliv introduced thorax airbags for side-impact protection in 1994 [24]. The goal ofthis bag is to keep the occupant away from the impact zone and to damp the slap fromthe intruding side of the vehicle. The thorax bag, mounted in the seat, is inflated within12 ms and typical volumes are about 12 litre. The electronic control unit is located inthe backrests of the front seats and the sensor is located in the sill or the B-pillar. Anextension from the regular thorax bag is the head thorax bag, which covers the chestarea as well as the head area.

Side protection systems for today and near future are described by Volkswagen [17]. Toimprove side impact occupant protection several steps were taken in the past. The firststep was to raise the stiffness of the car’s side structure to reduce the collision speedbetween door and occupant. The second step was to optimise the contact area betweendoor and passenger to distribute the force and avoid localised loads. The next step wasthe introduction of a side airbag system, like a combined thorax pelvis airbag, that hastwo functions: equal pressure distribution and early contact between door and occupantto accelerate the occupant at the lowest possible risk. Disposal of airbag modules ismentioned as an important aspect, which influences for example gas generator types(preferably without azide). Volkswagen introduced a fault-tolerant side-bag module; incase of no-intrusion, vent holes at the backside are not closed and the airbag is notdeployed. In case of intrusion, the intruding door closes vent holes.


Interaction of the hand and wrist with a door handgrip during static side airbagdeployment using CVS/ATB multi-body simulation program was studied by Universityof Virginia Automobile Safety Laboratory [12]. The objective was to quantify therelative severity of various hand- and handgrip positions to select a general test matrixfor laboratory testing. Amongst others, handgrip length, angle, and spacing and initialposition and orientation of the distal forearm and hand were varied. Sensitivity of theresults to initial hand position and wrist orientation with respect to the handgrip wasshown. Furthermore, concerns about bio-fidelity of the current ATDs (in particularshoulder region) were expressed.

2.3.5 Potential of side airbags to improve safetyBecause the accident statistics are always some years behind and side and curtainairbags are not included in each vehicle on the road, not much accident data is availableshowing benefits of these airbags by accident statistics.

‘Comparison of real world side impact/rollover collisions with and without thoraxairbag/head protection system: a first field experience study’ was published by BMW[149]. 24 side collisions were evaluated, 14 without and 10 with head protection system/ thorax airbag (HPS/TA) of BMW. An increase in AIS 1 injuries was reported (head by29%, thorax by 3%, neck by 6%), except for the upper extremities (reduction by 4%) incase of HPS/TA, with respect to the cases with HPS/TA. No serious injuries werereported in side impacts in case of HPS/TA. Note that no statistically valid statementwas permitted with these available data.

Via the NHTSA Website, a recent ‘Powerpoint’ presentation was obtained (October2001) on real world experience of side impact airbags in the special crash investigations[118]. 55 side airbag cases were analysed. The study concluded that no fatalities havebeen attributed to the deployment of a side airbag. Only one case was reported in whichthe occupant was seriously injured by a door mounted side airbag. Furthermore it wasconcluded that head injuries were reduced by the head protection side airbag, but noestimation in percentages was given. It was found that passenger compartment intrusionis the primary contributor to fatalities in side impact.

Some additional safety benefit was observed for side head and thorax airbags in aGerman study [46]. However, due to the small number of cases the results can not becalled statistically significant.

2.3.6 Special head protection airbags and curtain airbagsCurtain airbags were introduced from 1998 onwards. To prevent head and neck injuries,amongst others Volkswagen introduced the head-bag, a curtain-shaped inflatablestructure, which emerges from the roof rail and protects the head of the occupant fromthe windows [17].

Autoliv [24] also introduced the first airbag for specific head protection on BMW cars(1997), called the Inflatable Tubular Structure (ITS). The ITS, installed in the head-linerabove the front doors, consists of a nylon tube that inflates to a diameter of about 15cm., see Figure 11.


Figure 11 – ITS (left panel) and curtain airbag (right panel) [24]

For development of curtain airbags; particularly important are system parameters likeinflation time, fill capacity, and the time the airbag stays inflated during side impact androllover crashes [13].

Deployment timing of side airbags is determined by airbag configuration, distance ofinflator to airbag and inflator mass flow characteristics. Simula Automotive SafetyDevices [43] presented an innovative inflator, designed to reduce inflation time forroof-rail airbags by means of using a linear charge in longitudinal direction within theairbag. The Distributed Charge Inflator (DCITM) contains a small flexible pyrotechniccord (the linear charge) which ignites through the length of the airbag within 2 ms and asustainer charge at the beginning of the airbag that maintains bag pressure for protectionin secondary crash events or rollovers. A DCI approach enables reduction of inflatorpackage size and enables faster filling of the airbag without increasing risk for injuriesin case of OOP situations. It was shown that the bag inflates faster with the DCIsystem, indicating that the time-to-position the airbag is smaller. At the same time, theinjury risk in case of OOP did not increase. It was concluded in this study that:Ö ‘time to position’ is not an accurate predictor of OOP injuryÖ new distributed inflation approach results in higher mass flow rate than

conventional systems, without associated OOP injury riskÖ reduced deployment timing with new distributed inflation system was reached

without increasing OOP injury risk.

Due to changing fleet composition and possibly related to the introduction of ABSsystems, the number of rollover accidents increases, see also section 5.1.1. Injuries inrollover accidents are mainly caused by ejection of the occupant through the side paneland head contact to exterior objects and interior surfaces. To reduce injuries in rolloverimpacts, curtain airbag systems were developed. For correct functioning of thesesystems, knowledge of occupant kinematics prior to the rollover is required to be sureon correct timing of bag deployment. Although curtain airbag systems should protectthe occupant, incorrect deployment could result in occupant’s injuries as well. Severalrollover initiation types are distinguished from which tripping is the most occurringtype (according to NASS data US). Ford and TRW [44] presented a study on dummyhead kinematics in tripped rollover tests and a new test method to evaluate the effect ofcurtain airbag deployment. The Deceleration Rollover Sled (DRS) was used to perform9 dynamic rollover tests in which side-window position (up/down), deployment-timeand “g”-level (height of curbs) were varied. Results of the dynamic test were used todefine a new static test, referred to as Head On Glass test (HOG), to study interaction ofthe curtain airbag with the dummy without performing full scale tests. It was concluded


that this new static test successfully could be used to measure the risk of injury duringairbag deployment.

2.3.7 Potential of head airbags and curtain airbags to increase safetyNo real world accident statistics on effectiveness of head airbags and curtain airbagswere found because of the relatively recent introduction of these protection systems.However, the use of simulation techniques for investigations towards effectiveness ofrestraint systems is reported more and more in literature. A virtual approach to developinflatable curtains was presented by Autoliv [45]. CAE based development of headprotection systems was described using advanced simulation tools to mesh, fold and re-integrate the inflatable curtain in the vehicle roof structure. The airbag model was usedto investigate and optimise interaction between the curtain and the upper interior trimparts as well as the system restraint performance for both in-position and out-of-position load cases. Future research directions were suggested in the field of improveddummy models and improved airbag gas dynamics to take into account gas flow effects.

The field experience study cited in the section ‘potential of side airbags to improvesafety’ also investigated rollover collisions with and without Head Protection Systems /Thorax Airbag (HPS/TA) [149]. 49 rollover crashes with BMW’s were analysed fromwhich 9 included a HPS/TA, and 40 did not. It was concluded that AIS 1 injuriesincreased using HPS/TA (head by 45%, thorax by 8%, upper extremities by 7%),compared to no HPS/TA, but only 1 AIS2+ injury was reported. It was stated that theHPS was responsible to a greater extent than the TA for the reduction of seriousinjuries. It is noted that no statistically valid statements were permitted because of thecurrently available data.

The EU rollover project (started July 2002, will run 3 years in total) has the objective toassist European restraint and vehicle manufacturers to develop effective rolloversystems in a cost efficient manner. After implementation of such systems, increasedprotection to members of European society who travel by car is expected [152].

2.3.8 Other airbagsThis subsection describes airbag systems that are currently on the market but notincluded yet in most ‘standard’ car equipment.

Knee airbags & pyrotechnic knee bolsterLeg injuries are the most frequent problem in frontal crashes for occupants who areprotected by airbags and wearing seat belts (about 40% of the injuries are leg injuries)[57]. Autoliv [24] introduced knee airbags in 1996. The airbag is mounted in the lowerpart of the instrument panel and deploys towards the occupant’s legs, hence preventinghard contact between the knee and the interior panel / steering column. Knee airbagsbelong to the standard equipment of 2003s Toyota Avensis.

Faurecia developed a pyrotechnic knee bolster and investigated its contribution to cardrivers safety by means of virtual testing [49]. To keep the clearance space between thelegs and the dashboard as small as possible to limit impact velocity, the knee padding ismoved as close as possible to the knees in case of a frontal crash by means of apyrotechnic activator. This pyrotechnic knee bolster improves car driver safety becauseof reduction of sub-marining risk, reduction of pelvis and chest acceleration, avoidingcontact between the knees and rigid parts of steering column and dashboards.


Footwell airbagsFootwell deformation during accidents can cause lower leg injuries and therefore,Siemens developed a foot airbag to be placed underneath the driver’s side carpet toreduce lower leg injuries [63]. Siemens states that in sled tests, the foot airbagdemonstrated a reduction of lower extremity injuries by as much as 70%. However, nofurther scientific publications or references could be found to confirm this statement.

Autoliv [63] is currently developing an inflatable carpet to protect car occupants’ feet,ankles and lower legs from the intruding footwell of a vehicle during crash. Lower limbinjury mitigation from this inflatable carpet was evaluated in sled tests with intrusion bythe University of Virginia [64]. Sled tests were performed at a velocity of 56 km/h witha belted hybrid III occupant and a simulated knee bolster and steering wheel airbag. Anew toepan intrusion system was successfully built to produce repeatable intrusion. Itwas concluded that the inflatable carpet has the potential to reduce lower limb injuryrisk from footwell intrusion for low severity injuries. However, design optimisation isneeded to enable optimal handling of both translational and combined translational androtational toepan motion.

2.4 Interior panels and retractable steering columns

In crash terminology, the ‘first impact’ is often defined as the real crash event, whereasthe ‘second impact’ is defined as the occupant hitting the car interior. The restraintsystems as described in the previous sections, amongst others, try to reduce the negativeeffects of the ‘second impact’; e.g. they try to prevent the occupant from hitting the carinterior. For this second impact, materials for car interiors also can contribute toreduction of injuries by softening the contact between the occupant and vehicle interior.For example, ‘soft’ knee bolsters are applied in the dashboard or steering column toabsorb kinetic energy of impact and to avoid contact between the knees and rigid partsof the interior.

Kettering University presented high-speed measurement of contact pressure and areaduring knee-to-instrument-panel (IP) impact events suffered from frontal crashes [66].The aim of the study was to present a new methodology to study contact mechanisms ofthe knee – IP contact event (measure the pressure distribution in time instead of acumulative pressure distribution measurement as normally used before). Previoushuman cadaver impact studies showed that increasing the contact area of the anterior(front) surface of the knee may significantly reduce injuries to knee, femoral shaft andhip. In the current study, sled tests were performed with similar impact velocities fordifferent knee bolster materials. The 5th % female Hybrid III dummy was equipped withan electronic pressure mat over the anterior surface of the knee to measure temporalpressure distribution as a result a knee-IP contact. Also femur and tibia loads wererecorded. It was shown that stiffer IP’s resulted in higher peak loads and lower contactareas. A limitation of this study is that the pressure mat sensors are designed to measureloads normal to the surface of contact, whereas dummy instrumentation may havedifferent orientations. Further the pressure mat generates a discontinuous signal, in thisspecific case the spacing between the sensing elements was about 7 mm.

There are two types of automotive instrument panels; hard and soft. The hard type is amono-layer type and consists mostly of polypropylene. The soft type consists of threelayers; skin, foam and core, from PVC, PU, PC, or ABS [69]. For the soft type, PVCdominated the market for the skin layer but PVC is being eliminated due to


environmental reasons and poor low temperature resistance in long term performance.Several articles on ‘new’ interior panel (materials) design were found of which a fewwith focus on safety issues are discussed below.

Materials used for upper interior-trim components must meet ECE/R.21, equivalent toFMVSS 201U targets for energy absorption (see appendix C.2.1 and C.2.2 for somedetails on ECE/R.21 and FMVSS 201u), but must also be ductile at low temperaturesfor proper performance during low temperature airbag deployment. Other criticalfactors for the material to be used include the ease of processing, aesthetics and costs.Typically, molded-in ribs are used for energy absorbing in the B-pillar. Traditionalinterior resins include engineering alloys, acrylonitrile butadiene styrene (ABS),polypropylene (PP) and PVC. Solvay Engineered Polymers investigated theperformance of thermoplastic polyolefins in automotive roof-pillar covers involved withinterior head impact and roof-rail or side airbag deployment [14]. From this study, itwas concluded that compounded thermoplastic polyolefins offer a good balance ofstiffness and low-temperature ductility in roof-rail airbag head impact and seat airbagapplications, with improved moldability and cost savings.

Hyundai Motor Company and Honam Petrochemical investigated the characteristics ofsoft thermoplastic olefin (TPO) to replace PVC in the skin of instrument panels [69].The effects on melt strength, viscosity and types of rubber were studied as well asvacuum thermoforming and physical properties (thermal and light resistance) of TPO. Itwas concluded that TPO must have over 50% of rubber and in that case showed thewanted ductile fracture.

In traditional instrument panel (IP) constructions, a metal cross-car beam and steelreinforcement parts were providing the stiffness of the structure. More recently (from1994 on), IP’s without a cross-car beam, called fully integrated structural IP, wereintroduced. In the integrated IP’s the stiffness and strength are provided by the plasticIP, which results in weight and cost savings. Dow Chemical described engineeringdevelopment of a fully integrated polypropylene (PP) instrument panel concept [68]. APP rubber modified compound filled with 15% talc was used. The integrated IP conceptwas tested successfully using computer-aided-engineering in an EuroNCAP ODB testscenario, a side impact situation and head impact interior tests. To meet the ECE/R.21requirements, the rib patterns used for reinforcement in the passenger-airbag regionwere optimised.

Another trend in automobile industry was to integrate the airbag door as part of theinstrument panel by using the seamless airbag door technology. Visteon developedseamless airbag technology for a hard molded-in-color polypropylene (PP) instrumentpanel [67]. Requirements for seamless airbags are on the one hand correct deploymentperformance over a wide range (-30 to 85 ºC) of temperatures and on the other handcomply government regulations on interior head impact. Whereas correct deploymentrequired a weak seam to enable correct airbag deployment even at low temperatures,head impact tests required a strong enough tear seam to prevent any panelcracking/sharp edges exposed after impact. The molded-in-color seamless passengerairbag subject of this specific study is currently on the market.

More generally, invisible passenger airbag door systems have been widely introducedthe last years and these increase the risk of small particles to be released from thedashboard with high velocity, see also section 3.2 on airbag induced injuries.


Amongst others, Daimler Crysler presented a pyrotechnic-assist collapsible steeringcolumn [9]. The objective is to generate steering column motion away from theoccupant and synchronize it with the airbag deployment. The idea is to release asteering column pin upon airbag deploying, which enables the upper and lower steeringcolumn telescoping together. The distance to the occupant is then increased and OOPinjury risk reduced. It was demonstrated that 50-75 mm collapsing distance cansignificantly reduce OOP injury.

2.5 Integration of safety concepts

Thusfar, this study focussed on functioning of the different restraint systems separatelybut this section will focus on integration of the different safety concepts. In particularmodern cars have a stiffer front structure and a very rigid passenger cell, which isdemanding for the safety systems and their interaction. The stiffer front structure is,amongst others, a result of more stringent regulations (i.e. crash tests with highervelocities that have to be passed).

Relations between some systems as described in this chapter are summarised by [103]and given in Figure 12.

Figure 12 – Schematic diagram of current production restraint system [103]

From Figure 12 it is clear that there is interaction between the control/diagnosticssystem of the airbag module and the firing of the pretensioners. How good thisinteraction works will strongly influence the total restraint systems performance.

A summary of restraint system performance in the field, divided in belt, airbag andairbag + belt was presented in the book titled ‘Airbag development and performance –new perspectives from industry, government and academia’ [104], see Figure 13. Theauthors’ most important conclusion is that there is room for airbag performanceimprovement. In particular important is improvement of discrimination between crashesthat require airbag deployment and crashed that do not. Increasing the deploymentthreshold is suggested to improve the performance.


Figure 13 – Summary of restraint performance in the field [104]


An attempt to answer the question whether the new restraint systems result in limitingthe risk for occupants involved in real crash conditions was done by [20] analysing theLAB database in frontal impact. Three groups of samples, related to model year andsafety equipment were identified:1. Accidents involving cars model year 1980-1990, no structural enhancement, 3-

point belt2. Accidents involving cars model year after 1990, with structural enhancement, 3-

point belt + driver airbag (‘Eurobag’)3. Accidents involving cars model year after 1997, with structural enhancement, 3-

point belt with pre-tensioner +4kN belt load limitation + airbag (approved incombination with the load limiting belt)

Some results of the study are shown in Figure 14 and Figure 15. Figure 14 shows thatimprovement of the vehicle crashworthiness in group 2, resulting in less intrusion to thepassenger compartment and higher occupant deceleration, increased the injury risk forthe thorax region of the passenger occupant. This is not the case for the driver, becauseof the driver airbag involved in group 2 vehicles. From group 2 to 3, a significantreduction of risk to both front seat occupants is observed as a result of the combinationof belt load limitation and head and thorax airbag. Only the risk of moderate to severelower limb injury is still very high, see Figure 15.

Figure 14 – Variation of risk of fatality and severe injury to front seat occupants as a function of cargenerations, in frontal collisions [20]

Figure 15 – Risk of minor to severe injury for abdomen and lower limbs, belted front seat occupants (LABdata 2002) [20]


Influences of airbags in combination with seat belt pretensioners on AIS1 neck injuriesfor belted occupants in frontal impacts were studied in [123]. 158 frontal impacts wereanalysed from which the crash pulse was available from a crash recorder. Only neckinjuries were considered in this study. It was concluded that airbags in combinationwith seat belt pretensioners resulted in a reduction of AIS1 neck injuries in frontalimpacts of 41% (± 15.2%). In lower severity crashes, i.e. for impacts with ∆V between1 km/h and 30 km/h, reduction of the AIS1 neck injury risk with 59% ± 18.6% wasfound for airbag and seat belt pretensioner equipped cars.

Better optimisation of belt and airbag performance as an integrated system could reduceinjury risk. The German Insurance Association, Institute for Vehicle Safety [46]concluded that optimisation of the interaction between belt/airbag regarding therestraint of pelvis and chest could reduce severe injuries in thorax region and lowerextremities. In particular aggressive impact of the knee against the dashboard wasshown to be important.


3 Side effects of restraint systems

In the previous chapter it was shown that improved restraint systems are responsible fora reduction of the number of fatalities due to road accidents in the last decade.However, each restraint system may also introduce a certain risk of injury caused by thesystem itself [40]. The additional risk induced by (in particular) airbag systems shouldbe weighed against their benefits. It is important to be informed on possible injury risksdue to restraint systems as reported in literature. This section first describes injuriescaused by belts and airbags. Next the risks of an occupant being out-of-position aredescribed, which is currently an important research topic in crash safety. Therefore aseparate subsection is dealing with OOP. Finally injuries to specific groups ofoccupants, like children, elderly and extreme tall, fat or short people are described.

3.1 Injuries caused by belts

Seat belts reduce the risk of fatal and serious injuries by about 45% [61]. However, inhigh-speed collisions, rib and abdominal injuries may occur in particular if the seat beltis not correctly positioned.

Abdominal responses to dynamically lap belt loading were studied in [18]. Althoughseat belts have been shown to be effective in reducing the number of serious injuries incar crashes, also ‘new’ types of injuries have been reported as a result of ‘sub-marining’. Mostly, antropometric test devices (ATD) are used in seatbelt tests.However, ATD responses and human tolerance levels related to amount of allowabletensioning are not yet well correlated and therefore, in this study, post mortem humansubjects (14) were used to study abdominal injury response and injury thresholds.Injuries were reported for peak lap loads varying between 6.0-6.8 kN with a subsequentstable lap load of 3.6 to 4.1 kN. Based on the experiments, the authors suggest that theratio between subject weight and size affects the injury results. From this study it couldnot be determined whether the injuries were caused by the peak load or later in thestable load period.

3.2 Injuries caused by airbags

Typical injuries caused by airbags reported in literature may be categorised as follows:1. Head and neck injuries2. Thoracic injuries3. Abrasions, burns, contusionsOnly limited fatal injuries were reported in literature. Generally, ìf injuries are causedby the airbag, these injuries are just ‘side-effects’ compared to the alternative situation(without airbags). This means that the cost-benefit of airbag systems is positive.

VSRC Loughborough University reported three fatal head injuries associated withairbag deployment [40] with a high degree of certainty. Amongst others, complicatedfracture of the skull was observed as cause for fatal injury. A strong blow of the airbagagainst the front of the head (being at close proximity of the airbag) caused the fatalfracture. According to VSRC, this kind of injury would not be identified in crash testsusing current test dummies.For thoracic injury case review, VSRC noticed that it was difficult to separate injuriesfrom seat belt loading, steering wheel interaction and airbag deployment. However, two


cases with fatal thoracic injuries were reported that were caused by the fact that thechest was in very close proximity to the steering wheel at time of airbag deployment.Abrasions, burns and contusions to the hands and arms were observed by VSRC.Movement of airbag across the occupant surface material causes abrasions. Burns arecaused by the hot gases coming through the ventholes (sodium azide burns extremelyrapidly to provide the nitrogen gas to inflate the airbag) and by airbag material thatslides. Contusions can be the result of the airbag striking the occupant.

Ocular injuries from high velocity objects were studied by Virginia Tech ImpactBiomechanics Laboratory [6]. Traditionally, airbag designs included a door with anopening seam to release the airbag. As described in the previous chapter as well, arecent trend involves eliminating the door and deploying the airbag through a seamlesspanel. This enables small foam particles to be released from the dashboard with highvelocity, causing ocular injuries to the occupant without touching the airbag. A finiteelement eye model was used to investigate ocular injuries and it was concluded that themodel was effective at simulating ocular impacts from various particles in the event ofan automobile accident. Simulation results agreed well with experimental results.Currently the eye model included material properties up to rupture and largedeformation could be taken into account accurately. Material properties were takenfrom literature and experiments on eyes ‘in situ’ will be developed to further refine themodel.

Recent (1997-2000) accidents involving upper extremity fracture associated with airbagdeployment were analysed by Kettering University [7]. Detailed injury levelinformation was obtained for a limited set of recent cases in which the driver or front-seat passenger suffered from fracture level injuries of the upper extremity as a result ofa crash including airbag deployment. Analysis showed that airbag deployment increasesthe risk of forearm fracture as a proportion of all upper extremity fractures and thatfemales are at increased risk of such injury. The reason of increased risk for femaleswas not explained in this study.

Impaired hearing was reported by the German insurance Association, Institute forVehicle Safety [46] in about 10% of 564 vehicles in which at least one airbag wasdeployed. From the 57 cases in which impaired hearing was reported, in 11 cases theimpaired hearing was permanent. This was particularly the case when both driver andpassenger airbag had been fired.

3.3 Out-of-position (OOP)

In the past, airbags were only developed for use with normal seated occupants (so called‘in-position’ occupants). Occupant – airbag interaction would only take place with acompletely deployed airbag and generic, mean size males were used as a referenceoccupant. The opposite of ‘in-position’ is out-of-position (OOP), in which the occupantis interacting with the deploying airbag. In case of OOP, the occupant is in closeproximity to the airbag, i.e. steering wheel or dashboard. Whereas airbags aredeveloped to reduce injuries, the interaction of the OOP occupant with the airbag duringdeployment may even cause extra injuries to the occupant.

As of November 1, 1997, NHTSA reported 87 crashes in the US in which thedeployment of an air bag resulted in fatal injuries [76]. Among these fatalities, 49 werechildren and 38 were adults. Fatalities were reported using rear-facing infant seats or


using no restraint at all for child or adult occupants. Also misuse of belts was reported,in particular for smaller children. In all cases, the occupants were very close to thedashboard when the airbag deployed. Because of their proximity, the children sustainedfatal head or neck injuries from the deploying passenger air bag. For some drivers, out-of-position situations as a result of ‘black-out’ were reported at the time of the crash.Most of the crashes occurred at relatively low speed.

The influence of airbag folding pattern on out-of-position (OOP) injury potential wasstudied by the Institute of Automotive Technology (TU Berlin) [8]. Four differentfolding patterns for a driver airbag were studied by means of simulation techniquesusing Pam-Crash. The influences of leporello folding (conventional folding, ‘L’), rafffolding (also known as petri folding, ‘R’), stochastical folding (‘S’) and z-folding(comes from the ‘peter patent’, ‘Z’) were studied. It was concluded that the foldingpattern strongly influences the OOP injury danger. Compared to the other foldingpatterns, the conventional folding pattern turned out to be the most ‘critical’ pattern forOOP injuries, see Figure 16.

Figure 16 – OOP injury danger for ‘head centred on module’ position for different folding methods [8](limit values are indicated in lowest two rows)

The study also showed the success of a combined design, test and simulation approachas a tool to investigate the influence of airbag design parameters on OOP injury anddevelop advanced airbags.

Driver out-of-position injuries mitigation was studied by Daimler Crysler [9]. OOPcountermeasures were illustrated by a combination of computer simulation usingcoupled structural/computational fluid dynamics scheme and laboratory tests. Thefollowing OOP countermeasures were discussed.− Reversible multi-stage and variable output inflator− Pyrotechnic-assist collapsible steering column− Recess airbag module cover with ‘I’ tear seams− Flexible airbag mounting with petal cover seams− Airbag with hood/band and dual tear seamsThese measures did not compromise the high-speed crash performance. Only part of thesimulated design proposals was verified with laboratory tests. It was illustrated that foraccurate computer simulation of a static OOP tests, very detailed information about theinitial dummy position and accurate mathematical dummy models are needed.


For details on inclusion of OOP situations in regulations, the reader is referred toappendix C.2.2.

3.4 Effects of restraint systems on elderly

Crash Injury Research and Engineering Network ‘CIREN’ is a multi-center researchprogram involving a collaboration of clinicians and engineers in academia, industry,and government in the US. The University of Michichan Trauma Center is involved inCIREN and studied mechanisms and patterns of traumatic injuries sustained by theelderly in motor vehicle crashes [106]. It was found that elderly (>60) are more likelyto obtain more serious injury and besides, the risk to life is significantly larger for agiven injury severity. In particular elderly are at much increased risk to sustain ribfractures, which are highly associated with fatality (whereas for young people, fracturedribs have little impact). Improvement in chest protection systems is thereforeparticularly important for elderly.

For older people, the range of joint motion decreases and the location of the shoulderbelt height adjustment may become a problem because of ‘stiffness’ of the elderly. Astudy of Delphi Automotive Systems [48] investigating comfort and usability of seatbelts showed that drivers over 40 years have more complaints regarding to comfort andusability of seat belts than younger drivers. For drivers over 55 years old, high beltpulling force and inappropriate and loose fitting of the belt on the body was shown to bea problem.

3.5 Effects of restraint systems on small children and child restraints

Although child restraints are not the main subject of this study, some attention will bepaid towards interaction of airbags with child restraints.

The Third report to Congress on Effectiveness of Occupant Protection Systems andtheir Use [114] of NHTSA (USA) included investigation towards child – airbaginteraction during crash. The problem was split into rear facing infants and forwardfacing children at the front passenger position. Although it is generally recommended toplace infants in rear-facing seats in the back seat if the vehicle has a passenger sideairbag, rear facing infant seats were located at the front passenger seat in the fatalitycases reported (11 cases in the US as of December 1996). During the crash, thedeploying passenger airbag interacts with the back of the rear-facing infant seat causingto crack or break the plastic shell. This caused fatal skull fractures and associated braininjuries to infant. Also neck injuries could be possible but these are difficult to diagnoseto infants and were not reported. The crash scenario for forward facing childrenassumes un- or improperly- restrained children who are in close proximity to the airbag(due to pre-impact braking) at the moment of the crash. The airbag then deploys into thechild’s chest, neck and face, causing fractures including fractures in cervical spine,bruising and laceration of the spinal cord and brain stem injuries. As a result of airbagcover contact, also knocked-out teeth and jawbone fractures were reported.

To decrease airbag aggressiveness, recently modifications were made to the FMVSS208 (frontal impact regulation in the US, see appendix C.2.2). The modified FMVSS208 includes the use of small dummies to represent small stature drivers and childdummies to limit the risk of injuries by airbags to children. The new additional testsinclude several static airbag tests (with infants and child dummies) to limit the risk of


OOP related injuries. The new FMVSS 208 will be effective from September 2003 on(for 20% of yearly vehicle production, for all OEM’s selling on the US market).

3.6 Effect of occupant characteristics on injury risk

The effect of occupant characteristics on injury risk and the development of active-adaptive restraint systems was studied by TRL and VSRC [77]. The objective was toidentify specific occupant characteristics for which active-adaptive restraint systemsmight contribute the most to injury reductions. 12605 car occupant records from the UKCo-operative Crash Injury Study (CCIS, phase 4 and 5) were analysed to establish theinjury risk for front seat occupants in frontal and side impacts. The occupantcharacteristics focussed at were the Body Mass Index (BMI) and the age. The mainconclusions of this study were- A greater proportion of older occupants sustain serious injuries- Some evidence was found that a greater proportion of heavier male drivers and

male drivers with high BMI sustains serious injuries- Some evidence was found that lighter female drivers and a greater proportion of

female drivers with low BMI values sustain more serious injuries.- Some evidence was found that taller males and shorter females sustain more serious

injuries.The main injury regions for frontal and side impacts were head and chest regions.Related to the conclusions as mentioned before, it was also concluded that occupantgroups that differ most from 50th percentile could benefit most from adaptive airbags.

A comparison of injury risk and pattern of injury for male and female occupants ofmodern European passenger cars was made by VSRC [133]. Accident injury data fromthe UK Co-operative Crash Injury Study (CCIS) was analysed for differences betweenmale and female occupants in accident circumstances and injury outcomes. Femaleoccupants were about 40% of the whole sample, of which one third of the driversinvolved and over half of the passengers involved. Soft tissue neck injury (likeWhiplash) was reported more frequently amongst women across front, side and rearimpacts. In frontal impact, female occupants appeared to be more vulnerable forskeletal chest injury and leg injuries. Therefore restraint system design (including theseat belt, pretensioners and airbag) focused also on women’s characteristics, could havepotential in reducing injury risk.


4 Trends in restraint systems

This chapter describes current and future trends in the field of restraint systems. Someof the systems described are already introduced in so called ‘concept cars’.

4.1 General trends

The general trend in nowadays occupants’ safety clearly is the development of ‘smart’restraint systems. These systems can be adaptive to take into account occupantcharacteristics during deployment.

Some other general trends from the field are summarised below:• More attention is paid to development of occupant specific systems and prevention of

lower extremity injuries.• Integrated systems with airbag design integrated in design of the vehicle instead of

attaching some sensors to the steering column (late firing of the airbag).• Improved seats with side wings for better performance in lateral impact.• Allow for automatically seat movement to reduce the delta v:

− in frontal crashes for passenger seats,− side movement of the seat (about 100 mm) in side impact.

• More attention is paid towards the safety of rear occupants.• Whiplash protection for rear seats by means of the self inflating head restraint that

presses air in a bag in the headrest, moving the headrest to reduce the gap betweenhead and headrest.

• Integration of advanced airbag and belt systems.

Potential effects of these new ideas are difficult to quantify as long as these are notactually included in vehicles on the road. Virtual testing could be a way to investigatethe potential of the systems.

4.2 Trends in tools for restraint system development

A clear trend is the introduction of more and more virtual testing in restraint systemdevelopment. Using virtual simulation techniques, destructive testing can be limited andcosts are saved. Also injury risks for arbitrary sized people could be taken into accounteasily.

Tools for occupant protection analysis were described in [124]. In automotive crashsafety, the use of structural vehicle models in combination with multi-body basedoccupant models is common practice. This study showed two approaches forsimulation:1. coupling between MADYMO software that has specific occupant protection

features and the finite element crash program LS-DYNA2. modeling the vehicle and occupant in the combined FE-Multibody code

MADYMOBoth approaches were shown to be successful for a sled test model with a 50th

percentile dummy under NCAP conditions, however, CPU times were higher in case ofthe coupling.


The European project Proposed Reduction of car crash Injuries through improvedSmart restraint development technologies (PRISM) is a 3-years project that startedDecember 2002. PRISM has the following primary research objectives [109]:- To review existing European accident data and current "state of art" smart

technologies, to assess the potential effects of smart restraints on the Europeanaccident statistics.

- To obtain European statistical data regarding the actual locations of occupantswithin vehicles, to allow determination of realistic worst case occupant "event startpositions" for impact events.

- To investigate the effects of pre-impact occupant kinematics, (for example underpre-impact braking) to determine worst case occupant "impact start positions"

- To identify impact / occupant scenarios worthy of detailed study and to evaluate theissues and likely effects of smart restraints on those scenarios.

- To identify, create and use advanced computer models that allow the effectiveevaluation of such scenarios.

- To generate standard guidelines to define and evaluate the functional requirementsof smart restraints.

Equipment of all vehicles with ‘black boxes’, that give the crash pulse data and thedeployment characteristics of any multistage restraint system, could improve accidentanalysis. With the improved accident analysis, effectiveness of the latest airbag designscould be estimated easier and in that way, accident analysis facilitates future restraintsystem development.

4.3 Trends in safety

4.3.1 Investigation of multiple impactsIn the past, the focus in safety was on single accident modes like frontal impact, rearimpact, side impact and rollover. However, often accidents on the road are acombination of these accident modes. For future safety research, the focus will also beon the multiple impact problem. Irreversible restraint systems work in the first impact.When a second impact takes place, the restraint systems ‘did their job already’ and cannot be effective a second time. Therefore reversible restraint systems could contributehighly to improvement of occupant safety.

Consequences for occupant protection measures in multiple impact crashes werestudied in [122]. Two databases were used: the CCIS (UK, cases from 1992-2000) andthe MHH/GIDAS (Germany, cases from 1996-2000). The following impact types weredistinguished: single front, single side, single rear, single rollover and multiple impact(i.e. accident sequences in which vehicles undergo more than one impact). Multipleimpacts were, after frontal impacts (43.6-45%), the second common impactconfiguration (26.5-29 %). Multiple impacts represented an increasing proportion ofaccidents for higher injury severity cases. It was concluded that the head is the bodyregion that is most frequently injured in multiple impacts, but also injuries to the neck,chest and upper extremities were reported. Some consequences for occupant restraintsystems were considered.• Phased deployment of different protection systems in the different impacts• Increased duration of inflation


• Multiple inflation of airbags (re-inflating)• Position of occupants as a result of first impact (may be different from ‘normal’

seating position)• Time period covered by sensors, control modules and deployment algorithmsThe importance of multiple impacts in terms of frequency and injury risk was shown.

4.3.2 Safety of rear occupantsSafety of rear occupants becomes more important since more occupants are using rearseats of vehicles [132]. In this reference, the distribution of serious injuries wasassessed for belted and unbelted rear occupants for various impact directions. Lap-shoulder belted rear occupants experienced injuries of the thorax related to the shoulderbelt. The lap belted rear occupants, the lap belt was the most common source ofabdominal injury, as well as the spine (secondary). For unbelted rear occupants, theextremities and the head were injured by the B-pillar, seatback and other interior parts.This field data analysis of rear occupant injuries resulted in the following priorities forrear occupant protection, see Table 3.

Table 3: Priorities for rear occupant protection according to [132].

For belted occupants For belted & unbelted occupantsProvide load-limiting belts Energy absorbing (EA) material for seatbackCinch occupants to the seats Reduce contact with side interior and B-pillarImprove restraint geometry EA material for side and interior structuresReduce contact with and pad the seatback Inflatable side curtains, laminated side glassInflatable belts Improved containment in the rear seat area

Effects of optimised restraint systems for rear seat passengers were studied by means ofvirtual testing [119]. A MADYMO model was validated with sled tests. With thevalidated model, parameter studies were performed to determine the parametersinfluencing dummy loading, like anchor fitting buckle, upper fastening point shoulderbelt, belt slack, foot position, seat ramp, load limiter, crash pulse, pretensioner.Chest deflection was reduced with 10 mm using force limiters, 6 mm using a softervehicle pulse and approximately 5 mm using a pretensioner. For the chest injurycriterion ‘V*C’, the use of pretensioners resulted in largest reduction. The optimal forcelevel for the load limiters was shown to be dependent on space for the rear seatpassenger to move without touching the interior of the vehicle. For further studies, theinclusion of 5th % and 95th % dummies was suggested.

4.4 Trends in belt design

Some trends in belt design are described below.

4.4.1 Four point beltThe traditional three-point belt system has drawbacks in the field of ease of use, belt fitand comfort for elderly or ‘non-average’ sized persons. An alternative is found in afour-point belt system. The optimal location and acceptability of a suspender style four-point safety belt system to help improve fit, comfort and safety was identified by FordMotor Company and Lear [19]. In total 44 volunteers were involved. Acceptability ofthe new system was improved by avoiding an interaction between the shoulder belts and


the volunteer’s neck. The interaction between the shoulder belts and the volunteer’sneck was dependent on the horizontal and vertical position of the shoulder belts and theoccupant’s gender, weight and cloths.

4.4.2 New belt concept – inflatable beltA historical overview of inflatable belts and the benefits of inflatable belts in reducingserious injuries to vehicle occupants during crashes was presented by Goodrich [21].Development of inflatable belts started in early 1970’s but many concerns (includingcomfort and packaging) held back incorporation in passenger vehicles. Since then,much progress was made in the technical field and according to technology,introduction of inflatable belts is possible. Inflatable belts provide protection to vehicleoccupants during multi crash modes (frontal, side, and rollover). Since the belt isalready positioned at the occupant, it provides quick restraint in case of a crash. Beltloads are distributed over a larger contact area, which reduces the probability oflocalised load presence. In particular elderly benefit from inflatable belts. In case of sideimpact or rollover, the inflated belt on the shoulder supports the head and neck toreduce the lateral movement. Also out-of-position studies with children and theinflatable belt were performed and it was concluded that all injury limits are met easily.Using inflatable belts in combination with the airbag could enable changing of energyabsorbing capabilities of the airbag (reduction of aggressiveness).

4.4.3 New belt pretensionersSimilar development were reported by different manufacturers:• Reversible pre-tensioning seat belt (retractor with electronic motor), (TRW

system).• Reversible pre-pre-tensioning (Autoliv system), to give a more gentle load

distribution on the occupants chest in the event of a car crash. The first tightening isdone with an electrical motor, and this eliminates the slack in the belt system earlierthan with the normal pretensioner. This process can be reversible. Only in case of acrash event the ‘normal’ pretensioner is activated. The new system is expected tobe effective in preventing occupants from being thrown forward during severebraking.

Human tolerance levels of pretension for reversible seatbelt tensioners in the pre-crashphase were studied in [131]. Effects of the reversible seatbelt tensioners that generatelower belt forces and velocities but show performance characteristics over a longerperiod of time in contrast to pyrotechnic seatbelt tensioners were studied. Volunteertests were performed, using a stationary vehicle fitted with a prototype of a reversiblebelt pretension system. It was concluded that the loading applied by the prototype of thebelt pretensioner was tolerable / acceptable for the test persons. However, risk groupslike pregnant women or elderly) would need separate assessment of their potentialinjury risk. It was emphasised that the research is on-going, amongst others with drivingtests and repeated examination through volunteers.


4.5 Trends in airbags

Some trends in airbag design are described below.

4.5.1 Airbag designTrends in airbag design are strongly related to so-called ‘smart’ airbags usinganticipatory sensors (see also chapter 5 and 6).

Trends include:• Adaptive airbags which are variable in airbag size and airbag firing time.• New airbag venting systems, including multilevel venting systems to better control

the airbag pressure [103].• Folding patterns to focus on radial expansion.• Multiple compartment airbags [103].• New airbag materials with controlled fabric porosity so that discrete ventholes

could be eliminated [103].• Introduction of new airbags like centre curtains, front airbags for rear seated

passengers, etc.• Firing of curtain airbags in frontal crashes as well.• Cover properties, like cover stiffness, opening geometry, rotation points that are

located deep in the steering wheel [115].• Modules located in top mounted position for passenger side [115]• Active module that moves ‘backwards’ in the dashboard upon firing [115]

4.5.2 Inflator technologyFor inflator technology the following trends were found in literature:• Variable inflators – the control module simply requests a certain power level (out of

a continuous range) instead of making a choice between 2 or 3 prescribed levels[104].

• Further introduction of non-azide propellants to replace the sodium azide propellants.The new propellants have lower temperature gas with no particles and thereforepermit for example the use of lighter weight airbag fabrics [103].

• Hybrid inflators which use high pressure stored gas in conjunction with pyrotechniccharge. These have lower variability in performance [103].

• Heated gas inflators with a mixture of dry air and hyrogen gas under high pressure.These inflators are cleaner and environmentally friendly and also permit the use oflighter airbag fabric [103].

4.6 Sensors

Sensors are needed to enable development of adaptive restraints systems that can reallyact dependent on the specific situation.

Current sensors in airbag systems are only crash severity sensors [103]. These sensorsdetect changes in velocity and acceleration of the vehicle and decide to deploy restraints(airbag, belt pretensioner) or not. Current limitations of airbag performance are a resultof insufficient information about the crash event and the occupant characteristics. New


sensors and integration of information from different sensors can be applied to improverestrain systems performance, see Figure 17 for an overview.

In relation to belts; sensors can be used to obtain the following information- Belt use sensors to determine if the belt is used- Belt spool-out sensors to assist occupant size detectionFor airbag systems:- Crash severity sensors to determine the type and severity of a crash- Occupant classification like presence, weight, size, age and gender- Sensors to measure proximity of the occupant to the airbag moduleSeat (position) sensors could be used to assist estimation of driver characteristics andproximity. Decision algorithms should be suited to deal with all this new information.

Figure 17 – Advanced safety restraint system schematic diagram [103]

One promising trend to enhance the capabilities of restraint systems is to implement“intelligence” by using anticipatory sensors to be able to start acting earlier in the crashevent. These new safety systems are part of Intelligent Vehicle Systems (IVS) and willbe addressed in the next chapter in more details.

How advanced airbag regulations will effect non-FMVSS test procedures for vehicleseats is described by MGA Research Corporation [74]. In response to the new FMVSS208 (see appendix C.2.2), vehicles in future will have electronic sensors located in theseat and could also be equipped with other advanced sensor systems. The sensors willbe developed for measuring occupant weight and size and the output is to be used tocontrol the airbag deployment. The reliability of the sensors during the entire life of avehicle is essential for the vehicle’s safety performance. Since sensors are also added tothe seats, seat suppliers will have to deal with the increasing design complexity and


extended validation testing. New test procedures for seat durability testing wereproposed, taking into account avoiding damage to seat-mounted airbags and its wiring.

4.7 Potential effectiveness of adaptive restraint systems

Potential effectiveness of adaptive restraint systems was predicted by AutomotiveSafety Centre (University of Birmingham, UK) and Vehicle Safety Research Centre(Loughborough University, UK), [121]. ‘Injury Severity Reduction Matrices’ wereproduced for each driver group (shorter drivers, heavier drivers, older drivers and allother drivers) and all crashes (all low energy, moderate energy & low intrusion,moderate energy & high intrusion, high energy & low intrusion, high energy & highintrusion). Potential injury reduction for a certain group of drivers, given the crashseverity and type of injury, was estimated by logical progression. Both pessimistic andoptimistic potential reductions in the severity of injury to any body region wereassigned, providing a (by nature subjective) range. These matrices were then applied toCCIS accident data from 1992-2000. The potential effectiveness is given in Figure 18.

Figure 18 – Potential effectiveness adaptive restraint systems [121]

The overall effectiveness of adaptive restraint systems for MAIS 3 injuries wasestimated between 14% and 25% and for MAIS 2 injuries between 33% and 41%. Themethod used, including the Injury Severity Reduction Matrices, is ‘subjective’, but itwas intended to calculate a range of results, based on a range of possibilities, for afuture theoretical adaptive restraint system.


5 Intelligent Vehicle Systems (IVS)

In passenger cars, technology is taking over tasks of drivers in order to increase thelevel of safety and comfort. “Intelligent Vehicle Systems” are the key to achieve thistask. Each system including sensing of the outside and/or inside vehicle environmentand lead to an action for driver safety or driver comfort after that the sensor data havebeen processed is called Intelligent Vehicle System or IVS. Intelligent Vehicle Systems(IVS) are part of Intelligent Transportation Systems (ITS). ITS are the systems used toachieve mobile and safer traffic conditions by providing a link between the drivers,vehicles and the infrastructure. Electronic communication and computer-controlledtechnology [41] provide this link. Figure 19 provides an overview of the possibleactions performed in the field of IVS.

Figure 19 – Different type of actions performed by IVS [145]

Figure 19 provides an overview on the measures that can be performed for comfort orfor safety purpose in the frame of IVS. In this report the focus will be on safety. Theactive safety measures reduce the probability of an accident to occur. Passive safetymeasures allow the mitigation of crash effects during the accident and tertiary safetyinvolves rescue measures.

5.1 IVS in vehicle safety applications

The applications covered nowadays by the intelligent vehicle systems involve bothcomfort and safety applications. The requirements for safety are more complex anddifficult to fulfil than the requirements for comfort. One rising question is: ‘What is theadded value of IVS systems for safety?’ A key answer to this question is that IntelligentVehicle Systems for Safety (IVSS) tackle the first well-known cause of road accidents,namely, driver errors. Already in 1979, a study performed by Indian University showedthat driver errors contribute to 93 % of the accidents [129].


In a study on driver behaviour NHTSA found that 99% of the accidents investigatedwere caused by driver errors [93]. The errors can be of different types like delay torecognise potential risks, misinterpretation of the traffic situation, errors during amanoeuvre etc… In any case the misperception is a major factor.Moreover, IVSS allows an integrated approach for safety creating a link between activeand passive safety. The potential of IVSS to integrate both passive and active safety willbe described in this report. Some active safety systems like ABS and ESP (describedbelow) include intelligence and can also be considered as IVSS. These “conventional”IVSS take into account parameters concerning the driver and/or the vehicle behaviour.

5.1.1 ABS Anti locking Brake System or Antilock Brake SystemThe original acronym ABS is derived from the German term "antiblockiersystem." Thesystem was first patented in the 1936. The first series production started by Bosch in1978. ABS prevents the locking of the brakes. Sensors provide information of lockingto the controller, which releases the brakes momentarily. The modulation of the brakepressure level improves the efficiency for deceleration. ABS was designed to decreasethe probability of crashes by increasing deceleration and controllability and is thenconsidered as an active safety system. In some references, ABS is described as a crash-avoidance technology [51] [83]. Kahane found that, with the introduction of ABS,involvement in multi-vehicle crashes involving fatalities on wet roads weresignificantly reduced by 24 %, and non fatal crashes by 14 % [79] [80]. A February1996 study found ABS to be associated with approximately a 10 percent overallreduction in crashes [50]. Some statistics shown however an increase of rollover crashesafter the introduction of ABS. This last side effect could not be demonstrated bycontrolled experimental research [50] [51] [52].

5.1.2 ASR Acceleration Slip RegulationAlso called Electronic Traction Control (ETC). The ASR can be seen like an ABSworking in the accelerating phase or an inverted ABS. Many of the principles of theABS are used for this technique. The ASR allows an efficient acceleration allowing thedriver to remain in control of the vehicle in wet conditions.

5.1.3 ESP Electronic Stability ProgramESP is based on other electronic braking systems like ABS and ASR. The differentsensors records are monitored and compared to a reference model. The aim of usingESP is to reduce the risk of skid, drift or slide. It is too early to provide realisticnumbers on the effect of ESP on traffic accidents. According to the manufacturers oneof the strengths of the Electronic Stability Program is the speed with which it worksproviding high potential for safety [81] [82]. An analysis of the European AccidentCausation Survey (EACS) [128] shown that ESP would have reduced the likelihood oravoided the accident in 18% of all injury accidents and in 34% of fatal accidents. Thestudy was performed on information obtained from 1674 accident in Europe. Theanalysis is based on experts’ opinion and is illustrated in Figure 20.


Figure 20 – Potential of ESP for collision avoidance from Reference [128]

5.1.4 Adaptive Cruise Control (ACC)The new features concerning IVS is that the ‘far’ environment around the vehicle is alsotaken into account. This is made possible by the use of remote sensing technology (thesensors used in automotive applications are described in chapter 6).A promising IVS system introduced in the market and described sometimes as activesafety system is the Advanced (or Adaptive) cruise control ACC. ACC is presented bycar manufacturers to their clients as an IVS for comfort but it can be considered asbeing at the edge with IVSS. Mercedes launched the first European ACC system in thenew S-Class model at the end of 1998. Instead of static speed control with an ordinarycruise control, ACC adjusts the speed by detecting the distance and the relative speed ofa vehicle ahead using an onboard radar system (radar sensors are described in chapter6). The results of two driving simulator experiments using ACC [78] showedlimitations to the introduction of ACC's to road types other than the motorway. Safetyimprovement in the case of rear impact was studied in the European project DIATS[84]. In Figure 21, the comparison of simulation results obtained by three partners isshown. For this case, the test scenario included one ACC equipped vehicle following avehicle decelerating harshly with in a stream of vehicles.


Figure 21 – Safety benefits of ACC during emergency braking by simulation [84]

It appears that no accidents due to ACC malfunction or driver misunderstanding havebeen reported until now. It is again too early to take conclusions on the effects of ACCon safety because of the short time in which the systems are used and the limitednumber of vehicles using it. Some conclusions on ACC potential and effects onregulations obtained from a study performed in the frame of the EC funded projectDIATS [84] are reported hereafter:• ACC is unlikely to have significant impacts on the traffic efficiency of motorways in

the near future. Penetration rates below 20% have been shown to have little impact.In addition, it seems likely that drivers will choose not to use ACC systems nearintersections when lane changing is frequent as first generation ACC systems will notsatisfactorily respond to cut-in manoeuvres.

• ACC greatly enhances the longitudinal control of the driver, reducing accelerationvariation by about 45% compared to normal following, which will establishenvironmental benefits.

• There may be added value to smoothing flow with Variable Speed Limits whensignificant ACC penetration exists. VSL reduces lane changing and creates smootherdriving conditions better suited to ACC.

• A long term monitoring study should be undertaken to examine potential changes indriver motivation and driver skill on the network brought about by ACC. Safetybenefits are estimated due to the improvement in reaction times that ACC will offer.However, some concerns exist regarding driver’s ability to resume control in anemergency situation and the potential for drivers to recognise these situations later.

• The effects of further penetration of ACC will depend upon the time headwayselected by drivers. Currently, headways of 1.2 seconds and below are estimated tobe required to avoid reducing capacity. It may not be desirable to encourage longplatoons of vehicles with an inhomogeneous mix of vehicles, with different levels ofmaintenance and different control algorithms to operate in the fast lane.

• It may be necessary for national administrations to modify the driving code ofpractice to take account of the improved vehicle and control technology.

5.2 IVS potential to integrate Passive safety and active safety

Figure 22 is obtained from the EC funded project ADASE [54] (more European projectsrelated to this issue are listed in Appendix B). The figure provides a holistic approach to

[Km/h] [m]


safety in which the overlap of passive and active safety is shown. Note that the pre-crash phase in this case includes both collision avoidance and occupant protection.

Figure 22 – Holistic view on safety [54]

The Pre-Crash phase is related to a new field in automotive applications: Pre-crashsensing. Pre-crash sensing systems (branch of IVSS) are described in more detail in thenext section.

5.3 Pre-Crash Sensing (PCS) systems

Pre-Crash Sensing (PCS) systems are based on the three functions of IVS:• Sensing: To detect the relevant obstacle into the traffic and the infrastructure,• Monitoring: To inform the vehicle of the obstacle characteristics and• Acting: To take decision for automatic deployment of passive safety devices and/or

active safety devices to mitigate and/or to avoid the crash.

Current passive safety devices can be subdivided in systems that are deployed in theinitial stage of the crash like restraint systems (details are given in the first part of thisreport) and systems that do not need activation (e.g. padding). Besides that, most ofpassive safety devices could be deployed before the crash occurrence in combinationwith active safety actions by the use of the so-called pre-crash sensing systems.

Pre-crash sensing is related to all the crash modes• frontal impact,• side impact,• rear impact and• rollover

Daimler Chrysler developed a so-called “pre-crash sensing system” and implemented itin the Mercedes S class. The PCS includes a belt retractor developed by TRW, which isactivated by the information provided by the ABS (Anti locking brake System) and ESP(Electronic Stability Program) sensors and emergency braking. These two active safetysystems are activated in the collision avoidable state. The system is aimed to enhance


the functioning of passive safety systems like airbag in case of accident by avoidingOOP occurrence (see chapter 3).Toyota developed a similar pre-crash sensing system activating pre-crash seatbelts andbraking. The system in this case uses millimetre-wave radar to sense the vehicleenvironment and determine the possibility of collision with potential obstacles [150].

A European project “Chameleon” [29] performed in the frame of the 5th frameworkprogramme was dedicated entirely to PCS systems. It is interesting to highlight someoutput of this project.

5.3.1 Example project: Chameleon t[29]Figure 23 shows the intervention safety areas covered by chameleon compared to otherEC projects (see Appendix B for more information on other related EC projects). It isinteresting to note that this pre-crash sensing project does not include the avoidablephase (for the ADASE project mentioned above pre-crash sensing includes theavoidable phase).

Figure 23 – Pre-crash sensing in the chameleon project [29]

The relevancy of obstacles for pre-crash sensing applications was studied within theproject. According to accident statistics and their own (passive) protectionrequirements, the 5 car manufacturers involved in this project have given their detectionpriorities (Table 4).


Criteria Type PSA Renault Porsche Volvo CRF RankPole/Tree 1 2 1 1 1 2 (6)Wall 2 4 2 2 1 3 (11)SecurityRail

2 4 2 2 1 3 (11)

Infrastructure Fixedobstaclesinto theenvironment Ditch 4 5 3 3 4

7 (19)

Car 1 1 1 1 1 1 (5)Truck,bus

1 1 2 1 1 2 (6)

Pedestrian 2 2 3 4 4 5 (15)Bicycle 2 2 3 3 3 4 (13)Motorcycle

2 2 3 2 2 3 (11)

Traffic Potentiallymovingobstacles

Animal 3 3 4 3 3 6 (16)(1 → most important, 5 → less important)

Table 4: Obstacle detection priorities in the chameleon project [30]

The types of obstacles were then classified into three categories:

- obstacles which must be absolutely detected → car, truck, pole and tree,- obstacles interesting to be detected → wall, security rail, motorcycle, bicycle,- obstacles out of CHAMELEON interest → animal, pedestrian, ditch.

Note that Pre-crash sensing systems for pedestrian protection were taken out of thisproject. The reasons for this decision were not described in the documents used for thissurvey.

5.3.2 Pre-crash sensing potential and limitations to increase safety

Pre-crash sensing systems are introduced in the market since short. The social costbenefits depend on many factors like the type of safety measure to be deployed, thelevel of false alarms and the new type of risks generated. The main recognised benefitof pre-crash sensing systems is definitely “time”. In many accidents a relatively longtime (in the range of seconds) passes from the accident-causing event to the actualimpact [55]. In the “conventional” passive safety systems this time is not used at all tomitigate the crash. Pre-crash sensing systems can be used in both self-protection andpartner-protection (e.g. for cars compatibility purpose). PCS have great opportunitiesfor protection of vulnerable road users. PCS facilitate both post-impact and pre-impactcountermeasures [83].In the Chameleon project described above, the potential of passive safety systemsdeployed by pre-crash sensors has been investigated on the basis of simulation studiesand experts opinion. A resuming evaluation is shown in Figure 24.


Figure 24 – Potential of Pre-Crash Sensing systems References [29]

The main apprehension of these systems is false alarm and missing alarm risks:associated active safety measures such, as breaking unnecessarily could be dangerousfor the driver. Unnecessary deployment of passive safety measures, as airbags etc. couldalso be dangerous for the occupants. It is foreseen therefore that reversible safetysystems will be used at a first stage with limited or no consequences on driver safety.The responsibility (driver/manufacturer) in case of system failure is also an importantconcern. These issues are addressed in the European projects RESPONSE andRESPONSE2 (see appendix). As for all IVSS, an important potential of Pre-crashsensing is that the systems allows an integrated approach for safety linking passivesafety measures and active safety measures. This issue (passive-active safetyinteraction) is under study by the European Enhanced Vehicle Committee: EEVCWG19 (See appendix C).

5.4 Trends in IVS for safety

The implementation of advanced cruise control is a bigger step than it might seem forIVSS developments. ACC systems are described as “comfort IVS” but properknowledge of the vehicle surroundings can result in the following (future) applications:• Stop&go cruise control in a city environment• Country road ACC (automatic speed adaptation for curves)• Collision warning (forward and sideways)• Collision avoidance• Lane departure warning• Automatic lane-keeping / lane-change

These IVS are part of the so-called Advanced Driver Assistance ADAS (note that ACCis also an ADAS). Many European research projects besides the ones described aboveprovided studies on the potential of Advanced Driver Assistance (ADAS) systems toimprove safety, efficiency and minimise the environmental impacts of road traffic wasaddressed (see Appendix B for a list of some of these EC-projects).A first step to be taken is to use the obstacle detection systems for driver warning.Warning systems are already used for parking aid. Audible or visible signals are used towarn the driver on the proximity of danger. Even if false and missing alarms have lessinfluence on safety, it is vital that warnings not distract or confuse the driver during animpending collision. On the other hand one driver may not want to be warned until the


threat is severe while another driver may want to be notified at the slightest hint oftrouble [83].The best protection is of course to avoid the accident. According to Stephen N. Rohr etAl from Delphi [56], the collision avoidance systems (CAS) will evolve into threemodes:• Driver initiated• Vehicle initiated• A blend of bothThe actions concerned by collision avoidance are: steering and automatic stopping. Afully automated CAS is not foreseen to be introduced in the market in the next future.The reliability and the potential of the state of the art obstacle detection systems(sensors) is too small to be used in an unstructured environment like roads.

A road map for Advanced Driver Assistance Systems in Europe is presented in Figure25 obtained from the ADASE2 EC project [85]. The figure provides an overview of thecomplexity of technological issues and also expected safety enhancements.

Figure 25 – Road map for Advanced Driver Assistance Systems in Europe [89]

In Figure 26 [110] [111], an attempt to provide the trends of safety systems is shown. Inthis figure ADAS have a great potential of penetration in the automotive market. Notethat most of IVS systems for safety like ACC are depicted as active safety systems.


Figure 26 – Safety systems an their trends from reference [110]

A rather equivalent figure is provided by Themic [112] in which the ADAS are shownseparately, see Figure 27.

Figure 27 – Trends in safety systems from reference [112]

5.5 Discussion

IVSS have a great potential to enhance vehicle safety. In order to get precise overviewon IVSS potential, the capability of the used sensor should be addressed first. Theengineers involved in the design of the upcoming systems should have amultidisciplinary background to understand the requirements. New tools and/or linksshould be created between the design tools developed for passive safety (FE codes and


Multibody dynamics for passive safety) and the ones developed for active safety. Thereis a clear need to define the interconnections between passive and active safety via IVSand their influence on actual vehicle safety standards. The EEVC WG19 (see AppendixC) addresses this issue. New testing procedures should be developed for the design andvalidation of IVS.In the chameleon project (see appendix B) a simulation tool called EICAS was used fordesign and analysis of PCS purpose. In the Netherlands a large testing facility calledVEHIL is under development to test IVS [151]. This facility is aimed to be anintermediate step between simulation and full-scale road test.

The sensors are the key element for developing IVS for automotive applications, whichcan be used for safety purpose. One obstacle to the introduction of IVS used for safetypurpose is the difficulty of assessment of the false and missing alarm rate. New designand validation tools should be developed for this purpose (which could also be used todemonstrate the potential of these systems). Nowadays radar appears to be the mostpromising sensing technology. Artificial vision provided also promising results. Moredetails on radar and other types of remote sensors used in automotive applications areprovided in the next chapter.

The combination of different sensors would probably be the ideal solution (see nextchapter). However, the use of any remote sensor for safety applications is tricky forseveral reasons like driver acceptability, responsibilities in case of system failure andthe limitations of the actual sensors to cover a large angle. Regulations are also an issuefor remote sensing use in automotive application. The actual radar used for ACC use a77 GHz frequency, 24 GHz radar can cover a larger angle with a higher accuracy andresolution and lower production costs than 77Ghz radar. However, this frequency it isnot “yet?” allowed in automotive applications (see information on the SARA group inappendix C). The information obtained from the sensors should be more reliable andcomplete than its actual state. More details on sensor technology can be found in thenext chapter.


6 Remote sensor technology

Roughly 37% of serious road accidents (with injuries) occur in conditions of limitedvisibility, like darkness and fog [59]. Different types of sensors are (or can be) used toobtain information about the surrounding environment of the driver and/or the vehicle.The anticipatory sensors used in automotive industry are:• Ultrasonic sensors• Infrared sensors• Radar• Lidar• Artificial visionEach type of sensor operate in a frequency range of the electromagnetic spectrum (apartfrom the ultrasonic sensors) shown in Figure 28. Each sensor provides partialinformation of the surrounding world. The combination of these sensors could givebetter results than using them separately. In this chapter the sensors mentioned aboveare described and also the so-called sensor fusion.

6.1 Ultrasonic sensors

Ultrasonic devices work with sound waves with a frequency higher than human earperception (20 kHz). The main advantage of the device is their low costs. The limitationis the low scan rate (10 Hz) which is proportional to the sound speed. For this reasonthe ultrasonic sensors are restricted to low speed manoeuvres (e.g. parking aid).

6.2 Infrared sensors

There are two types of infrared sensors:1 Near infrared sensors (laser radar, infrared sensors) which do not offer a sensible

benefit in fog (0.35-2.5 µm).2 Far infrared sensors (sensitive in the range of 8-14 µm), providing thermal images

of the scenario independently from any light conditions. The enhanced visibility infog and heavy rain condition is dependent on droplet size.

Figure 28 – Classification of the electromagnetic spectrum [26]


6.3 Radar

The radar appears to be the most promising remote sensing technology for automotiveapplications. Radar is an acronym made up of the words radio detection and ranging.Radar is a device that detects the presence, the direction, and the position of objects byusing reflected electromagnetic energy. One advantage for automotive applications isthat radar is unaffected by darkness and is able to look through fog, clouds and snow tosome degree. The experts in Radar field use a specific terminology, for instance, theenergy reflected from an object is called echo, the distance from the radar to an object iscalled range. The object in this case is called target.

Two types of radar are generally used in automotive applications:The pulse radar: transmits very short bursts or pulses, each pulse being followed by arelatively long resting period during which the transmitter is switched off and thereceiver is operating. Since radar waves travel at the speed of light, it is possible tocalculate the range from the travelling time of the returning signal.

The Continuous wave (CW) radars: transmit a constant beam of radar energy. Asopposed to pulsed radar systems, continuous wave (CW) radar systems emit acontinuous electromagnetic radiation. If an object is moving, the radar waves returns toa separate antenna with a frequency that is slightly different than the originaltransmitted pulse frequency. Measuring this so-called Doppler Shift the speed of theobject can be determined. One limitation of pure CW radar is that the range to theobject cannot be determined. However, by manipulating the frequency of the radar overtime (Frequency Modulated Continuous Wave –FMCW), the object’s range can also becalculated from a CW radar. An advantage of FMCW radar systems in comparison withclassical pulse radar is the low measurement time.

Radar systems rely upon a portion of the transmitted radar energy being reflected off oftargets or obstacles to be detected. The reflective strength of a radar target is a measure,which has units of m². This ability to reflect energy is called Radar Cross Section orRCS. The RCS depends on shape, size, material properties and aspect angle. Typicalvalues for the radar cross section for different objects in square meters is shown in theTable 5:

pedestrian 1cyclist 2car 100Pickup,truck 200

Table 5: Typical RCS values

It can be seen that a radar system can detect a truck at a greater distance than it candetect a pedestrian.

ACC systems available on the European market are based on pulsed radar devices orfrequency modulated continuous-wave (FMCW) operating within the frequency range76 – 77 GHz. The maximum range for this type of radar is about 150 meters. An othertype of radar is the 24 GHz radar, which is not used in Europe because it is not allowed


by legislation (see info on the SARA group in appendix C). The motivation provided bycar manufacturers and sensor providers for using this technology is that it will enablemass-production (cost effective) and also that the 24 GHz radar allows both large angleand near field detection (needed for pre-crash sensing applications). Bosch point ofview concerning the use of radar for automotive applications in function of the usedfrequency is shown in Figure 29. In Table 6 some characteristics of the two radar areshown [35], [38].

Figure 29 – Possibilities of using radar in automotive applications in function of the used frequency from[39].

Parameter 77 GHz radarValue

24 GHz radarValue

Angular coverage inAzimuth

10° 50°

Minimum range 1 m 0.3 mMaximum range 150 m 20mRange resolution 1 m 0.03 mRelative speed interval -80km/h...+240km/h 0 to 216 km/hRelative speed resolution 2.5 km/h 0.1 m/s (closing

velocity)Time for complete scan 30 ms

Table 6: Comparison of 77GHz radar and 24 GHz radar


Figure 30 – Example of an ACC scan characteristics from [38]

More details on Radar applied to automotive applications can be found in references[30][33] [31] [33] [32] [37].

6.4 Lidar

The radar principle is also used in optics. LIDAR (LIght Detection And Ranging) orLADAR (LAser Detection And Ranging) can be used for automotive applications likeACC and pre-crash sensing. IBEO Automobile Sensor GmbH of Germany is actuallythe only supplier of such devices for the automotive market. For pre-crash application ahigh dynamic Laserscanner for near field scanning was developed in the frame of theEuropean project Chameleon [29]. The Pre-Crash Laserscanner measures distance,velocity, direction and outline of the obstacle with 40 Hz scan frequency and an angularresolution of 1.0°. The update rate is of 25 ms with a viewing angle of up to 270°. Atruck driving 3 m ahead of the test-vehicle is detected by more than 40 measurementpoints, that means a measurement point every 5 cm on the outline of the truck’s back.The Laserscanner is eye-safe (laser class 1) and has a single shot measurement accuracyof ± 5 cm (1 Sigma) with a max. range of 20 m.The Laserscanner creates a 2-dimensional range profile of the environment. The built-inDSP allows a high-speed object detection and the use of a high performance objecttracking algorithm for real-time tracking. The main limitation for the use of Lidar inautomotive applications is that weather conditions affect its potential.

6.5 Artificial vision : (video pattern recognition)

Reliable obstacle detection is one of the most important issues for pre-crash sensing andcollision avoidance systems. Artificial vision does not provide the range or the speed ofthe potential obstacles but can be used for the recognition of the surroundingenvironment. Other advantage of using a camera is that it can provide information onthe infrastructure and be used for lane keeping (follow the road and keep within thecorrect lane).Two techniques can be used: The monocular vision and the stereo vision. Theadvantage of analysing stereo images instead of a monocular sequence lies in thepossibility of directly detecting the presence of obstacles, which is, otherwise,


indirectly derived. The techniques will not be described in this report. More details canbe found in a survey on artificial vision performed on this item by M. Bertozzi et Al[87].

The system developed by mobileye [116] for driving assistance systems on basis ofmonocular vision can detect and track other vehicles on the road and includes ego-motion estimation and road geometry analysis. The literature shows many projects inwhich artificial vision is used for automatic vehicle guidance and/or obstacle detection[88] [89] [90] [91]. In a project called Urban Traffic Assistant (UTA and UTA2) astereo vision camera is developed by Daimler Chrysler which is able to recognisepedestrians, traffic signs, lanes and can be used for stop and go applications [92].The technology is not ready yet to be used in commercial vehicles. The artificial visioncombined with other remote sensing techniques like radar would provide promisingresults (see Data sensor fusion)

6.6 Data sensor fusion

The ideal solution to contain the production costs would be to use the same sensor fordifferent applications (e.g. ACC and pre-crash sensing). However, each of the sensortechnologies listed above has its advantages and inconvenient. In order to take oversome tasks of the driver the technology should imitate the human way of sensing. Thedriver uses simultaneously different sensors (in particular his eyes and his ears) tounderstand its environment. In sensor technology the simultaneous use of differentsensors is known as sensor data fusion.The data obtained by a single sensor give only incomplete information. A combinationof sensors data allows a better understanding of the surrounding world. Use of sensordata fusion generates however new problems. For instance, the data can be redundant orobtained at different time step.

The sensor data fusion is foreseen to be used in future cars equipped by both radar andartificial vision systems for target detection, classification, identification, and tracking.The literature shows that different techniques can be used like Bayesian methods, theArtificial Neural Networks, or the fuzzy logic method [27] [87] [105] [113]. Theobtained data obtained from each sensor are processed together to increase the level ofunderstanding of the surrounding world.

.


7 Conclusions

This chapter shortly presents the most important findings from this literature survey.

7.1 Restraint systems

This literature study showed the benefits of current restraint systems. Wearing seat beltsstill offers the biggest reduction of injury potential during a crash, regardless of impactsituation. For example, for frontal impact injury risk reduction up to 60%. The use ofseat belts in combination with airbags reduces the injury risk for frontal impact littlemore (plus 10-20%, compared to belt-only). However, the belt is often not worn in caseof a crash. Not much literature was available about field performance of side andcurtain airbags. These systems were introduced only recently and very limited accidentcases were available in literature. Still, some preliminary field studies and numericalsimulations seem to show benefits of new systems. Some ‘recent’ seat concepts claimreduction of Whiplash injury risk in case of (low severity) rear impacts and alsoreduction of fatality risk for high severity impacts.

Side effects of restraint systems were investigated in literature. Only limited seriousinjuries due to restraint systems were reported. To prevent occupants from being injuredby the airbag instead of being protected, more stringent airbag regulations will beincluded in the USA. The so-called out-of-position situation will be included in the newFMVSS 208. Since also in Europe close proximity to the airbags as a result of pre-crashbraking may occur, even when wearing seatbelts, these trends are important for Europeas well.

Current trends indicate the increasing importance of the use of adaptive systems. It wasshown that for the population that differs most from the standard 50th % theimprovement potential might be the biggest. Future trends also include more focus onthe second and later impacts in multiple impact events, as current systems protectreasonably well during the first impact. More attention is paid towards safety of rearpassengers.

7.2 Intelligent Vehicle Systems

There have been large reductions in fatalities in the last decade. However, still thenumber of fatalities unacceptable. IVSS offers new solutions to tackle road safetyproblems. The devices for obstacle detection used for ADAS and pre-crash sensingsystems in particular are foreseen to play an important role in the next generation ofvehicles. The “conventional” IVSS provide have a high potential on vehicle safety.Estimations from in depth accidents analysis showed that ESP could have reduced thelikelihood or avoided the accident in 18% of all injury accidents and in 34% of fatalaccidents. The remote sensing technology will play an important role in thedevelopment of IVS in general. Sensed information of the upcoming crash caneffectively be used to perform actions for the mitigation of the crash.A lot of research work was done on IVSS in the frame of European projects. IVS ingeneral and IVSS particularly introduce a new perspective on safety. IVSS tackle thefirst cause of accidents which is driver errors. IVSS will enhance safety also bypermitting an integrated approach to safety issues. A multi-disciplinary approach isneeded to develop IVSS. New simulation tools and testing procedures are needed for


the design and validation of the systems but also to show the potential of this relativelynew automotive application. Finally regulations will probably be modified because ofthe introduction of these tools.


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Appendix A.1/1TNO report 03.OR.BV.037.1/MRE | Literature survey ‘In-vehicle safety devices’ | 09 May 2003

A Glossary

ABS (Anti-lock Braking System)ABS keeps the wheels from fully locking up while braking to allowthe driver to maintain steering control. The maximum force on thebrake pedal slows each wheel to the point of maximum braking -without skidding.

ACC (Adaptive Cruise Control ):Maintain both the required cruising speed and the headwaybetween the vehicles acting on the accelerator and the brakingsystem. Single forward looking radar.

ADAS (Advanced Driver Assistance Systems) Examples of ADA systems : ACC, lane departure warning andcollision warning.

AGV (Automatically Guidance of Vehicles)

AICC (Autonomous Intelligent Cruise Control)The concept of AICC is similar to a conventional cruise controlsystem, which is now an accepted feature of most vehicles. The AICCsystem controls the speed of a vehicle with reference to the speed ofother vehicles on the road. This system has the potential to reducerear-end accidents in both city and highway conditions - particularlythose caused by driver inattentiveness

ATD (Anthropometric Test Device),also called ‘test dummies’. These devices represent occupants in crashtesting

ASR (Acceleration Slip Regulation)ATT (Advanced Transport Telematics)

AVCS (Automated Vehicle Control Systems )Refer to the group of ITS (or IVHS) concepts that actually control avehicle. It is this group of systems that are likely to have the mosttangible effect upon vehicle safety and the avoidance of accidents. Agroup of systems under the AVCS umbrella is known as AutonomousIntelligent Cruise Control or AICC

AVG (Automatic or Convoying Vehicle Guidance )AVG requires advanced environment sensing (e.g. radar) withvehicle-to-vehicle communication.

CAS (Collision Avoidance Systems)

DIAL (Differential Absorption LIDAR)

DVE (Design and Validation Environment)

Appendix A.2/2TNO report 03.OR.BV.037.1/MRE | Literature survey ‘In-vehicle safety devices’ | 09 May 2003

ECU (Electronic Central Unit)

ESP (Electronic Stability Programme)

FAST (Fully Automated Sensor Triggered actions)

FAV’s (Fully Automated Vehicles)

FMCW (Frequency Modulated Continuous Wave) or (Frequency Modulated CarrierWave) radar

HMI (Human Machine Interface )

HMIX (Harmonic Mixer)

HUD (Head Up Display)

ISA (Intelligent Speed Adaptation)

ISS (Integrated Safety System)

ITS (Intelligent Transportation Systems)

IVS (Intelligent Vehicle Systems)

IVSS (Intelligent Vehicle Safety Systems)

LAB (Accidentology and Biomechanics Laboratory - PSA France)

LASER (Light Amplification by the Stimulated Emission of Radiation)

LIDAR (Light Detection And Ranging)

MPA (Medium Power Amplifier)

OA (Obstacle Avoidance)

OD (Obstacle Detection)

OEM (Original Equipment Manufacturer)

PCS (Pre Crash Sensing)

TTC (Time To Collision)

VCO (Voltage Controlled Oscillator)It is an oscillator designed so applying a voltage to its control portor tuning port can change the output frequency

Appendix B.1/1TNO report 03.OR.BV.037.1/MRE | Literature survey ‘In-vehicle safety devices’ | 09 May 2003

B List of relevant IVS related EC projects

ADASE: Advanced Driver Assistance Systems in EuropeADASE is an EC IST funded thematic network that will help to

introduce and implement active safety systems. The objectives are:• to use the state-of-the-art knowledge to generate corresponding road

maps and guidance,• to facilitate the information exchange within the cluster of projects

related to ADA systems and transport,• to organise in-depth expert workshops on selected topics , and• to disseminate the resulting findings and information to all relevant users

and user groups and the general public.

ADVISORS: Action for advanced Driver assistance and Vehicle control systemsImplementation, Standardisation, Optimum use of the Road network andSafety.Based on test site demonstrations, a methodology is developed to assessthe impact of different types and different levels of penetration of ADASin terms of the safety, efficiency and environmental performance of theroad transport system. Furthermore, implementation scenarios isdeveloped in order to help introducing appropriate ADAS.

AWAKE: System for effective Assessment of driver vigilance and WarningAccording to traffic risK EstimationThe objective of AWAKE is to increase traffic safety by reducing thenumber and the consequences of traffic accidents caused by driverhypovigilance.

CHAMELEON Pre-crash Application All Around The VehicleThe main objective of the Chameleon project is to support, direct andvalidate the development of pre-crush sensorial system to detectimminent impact in all type of scenarios (urban, rural and motorway)

COMUNICAR: COmmunication Multimedia UNit Inside CARThe main goal is to design, develop and test an easy-to-use on-vehiclemultimedia Human-Machine Interface (HMI). Such HMI will managethe communicative exchange with the driver taking into account his/herworkload, the different environment conditions and traffic scenarios. Toreach such a goal, a set of Innovative Methods in the fields of HumanFactors, Multimedia Design, and Technological Devices for automotiveapplications are explored and developed. The final expected outcome is asafer and more comfortable driving

EUCLIDE Enhanced hUman machine interface for on vehiCLe Integrated Drivingsupport systEmsEUCLIDE will develop a new reliable integrated driver assistancesupport system, which will monitor the area ahead of the driver and will

Appendix B.2/2TNO report 03.OR.BV.037.1/MRE | Literature survey ‘In-vehicle safety devices’ | 09 May 2003

provide an effective support especially in cases of night and adverseweather conditions. This system will integrate the functionalities of radarand far infrared sensors resulting to a highly reliable and efficientsystem. At the same time a new enhanced HMI, based on the state of theart at EU level, will be developed. The proposed system is expected tothe market stepwise within the next 5 years .The main aim of the projectis to address the strong societal needs of reducing the total number ofaccidents. So the proposed project will strongly address human factorissues.

IN-ARTE Integration of Navigation and Anticollision for Rural TrafficEnvironmentThe aim of IN-ARTE is to develop an integrated autonomous on-boardsystem to be able to build an extended view of the environment in frontof the vehicle. This is done by integrating signals from anticollisionradar, road recognition CCD sensors and navigation map, in order toguide and warn the driver through an optimum HMI in a series of ruralareas related traffic tasks, such as intersection handling, speed selectionwhile negotiations, curves, obstacle detection, etc…

PROMETHEUS Programme for a European Traffic with Highest Efficiency andUnprecedented Safety

Started in 1986, led by 18 European automobile companies, stateauthorities, and over 40 research institutions with a budget of about 900million euros. The objectives fall in the following categories:− Improved driver information− Active driver support− Cooperative driving− Traffic and fleet management

RESPONSE II Advanced driveR assistance systEmS: from introduction scenariostowards a code of Practice fOr developmeNt and tESting. Projectfinanced in the 5th FP in the IST. Response 2 is the contimuation ofRESPONSE: Project developed in the frame of the 4th frameworkprogramme “Telematics Applications Programme” from 1998 to 2001.In this project legal issues regarding ADAS market introduction wereadressed. The work willl continue in the frame of a new projectResponse II.

Appendix C.1/1TNO report 03.OR.BV.037.1/MRE | Literature survey ‘In-vehicle safety devices’ | 09 May 2003

C Overview actual regulations and consumer tests

This chapter provides a brief overview of the current or near future regulations andconsumer tests that are related to restraint systems and IVS.

C.1 Introduction of organisations

The most important organisations working on and assisting regulation andstandardisation activities in the automotive field are described below.

C.1.1 ISO (International Organisation for Standardisation)Different Technical Committees can be identified within ISO, responsible for specificsectors of investigation.

C.1.2 EEVC (European Enhanced Vehicle-safety Committee)The EEVC was founded in 1970 in response to the US Department of Transportation’sinitiative for an international programme on Experimental Safety Vehicles (ESV) [65].Governments of France, Germany, Italy, the Netherlands, Spain, Sweden, the UnitedKingdom and Poland are members of the EEVC. The EEVC works via technicalworking groups, directed by the Steering Committee. The Steering Committee iscomposed of two representatives of all members; one person from the government andone person from a governmental research organisation involved in vehicle research. TheEEVC provides the link between government, research and development, industry,administration and regulation in the quest for safer road vehicles. It is not the role of theEEVC to develop vehicle regulations, but to act as technical advisor to the regulatorybodies like UN Economic Commission for Europe, working party 29. A steeringcommittee (composed of representatives of the members) directs the technical work ofthe EEVC, which is organised in working groups.

C.1.3 IHRA (International Harmonized Research Activities)The International Harmonized Research Activities (IHRA) were established under theESV Programme in 1996. IHRA aims to conduct world-wide harmonised research toestablish global regulations in the filed of side impact, compatibility & frontal impact,pedestrian protection, biomechanics and intelligent transportation systems.

C.1.4 IEC (International Electrotechnical Commission)The International Electrotechnical Commission is the leading global organisation thatprepares and publishes international standards for all electrical, electronic and relatedtechnologies and has an important role in the standards concerning IVS.

C.1.5 ISOThe technical work of ISO is highly decentralised, carried out in a hierarchy of some 2850 technical committees, subcommittees and working groups. In these committees,qualified representatives of industry, research institutes, government authorities,consumer bodies, and international organisations from all over the world come togetheras equal partners in the resolution of global standardisation problems [108].

TC 22 is concerned with road vehicles. TC 22 investigates all questions ofstandardisation concerning compatibility, interchangeability and safety, with particularreference to terminology and test procedures (including the characteristics of


instrumentation) for evaluating the performance of the following types of road vehiclesand their equipment:

• mopeds (item m);• motor cycles (item n);• motor vehicles (item p);• trailers (item q);• semi-trailers (item r);• light trailers (item s);• combination vehicles (item t);• articulated vehicles (item u).

C.2 Regulations related to restraint systems

Most important in this field are the regulations related to airbags and seat belts. Thereare large differences between the US and the EU and although our main focus is the EUsituation, attention is paid towards the stronger US regulations as well since these maybe followed in Europe as well in future.

C.2.1 EU requirementsIn the EU, vehicles have to comply ECE regulations. The ECE regulations include:• ECE/R12 for steering column behaviour during a crash• ECE/R14 for attachment points of safety belts• ECE/R16 for safety belts and attachment systems• ECE/R17 for seat strength and attachment• ECE/R21 for sharp interior parts• ECE/R25 for head restraint systems• ECE/R32 for rear end crashes (deformation of passenger compartment)• ECE/R33 for front end crashes (deformation of passenger compartment)• ECE/R35 foot well intrusion• ECE/R94 protection for frontal crash• ECE/R95 protection for side crashNote that currently, the ECE regulations do not include airbag requirements.

Besides the ECE regulations, there are EU directives which are often equal to the ECEregulations. In general, if the vehicle complies the ECE regulations, also the EU-directives are fulfilled.

C.2.2 US requirements

FMVSS 208The purpose of the FMVSS 208 is to reduce the number of deaths of vehicle occupantsand severity of injuries by specifying vehicle crashworthiness requirements andspecifying equipment requirements for active and passive restraint systems.The National Highway Traffic Safety Administration (NHTSA) published an amendedversion of the Federal Motor Vehicle Standard (FMVSS) 208 for occupant safety inmotor vehicles on May 2000. Changes in the FMVSS 208 were needed because of theTransportation Equity for the 21st Century “to improve occupant protection foroccupants of different sizes, belted and unbelted… while minimising the risk to infants,children and other occupants from injuries and deaths causes by airbags, by means thatinclude advanced airbags” [2].


Previously, the FMVSS 208 required all passenger cars manufactured after September1, 1997, to be equipped with driver and passenger airbags including sun visor warninglabels, along with manual lap and shoulder belt. For vehicles to be certified a 48 km/hfrontal barrier test or a sled test with 48km/h generic sled pulse (unbelted) and 48 km/hfrontal and oblique belted barrier tests with instrumented dummies had to be performed.The recent modifications to the FMVSS 208 include the use of small dummies torepresent small stature drivers and child dummies to limit the risk of injuries tochildren. The new FMVSS 208 will be effective from September 2003 on (for 20% ofvehicle production). The new additional tests include several static airbag tests to limitthe risk of OOP related injuries. The airbag systems must either inflate in a low riskmanner or suppress the deployment of the airbag if an out-of-position driver weredetected. For the passenger side, the system must inflate at a low-speed impact inflationrate, suppress the airbag deployment in presence of a child, or suppress the deploymentif the child moves close to the airbag during an impact [70].

Warning labels for airbags were specified by NHTSA in 1995 and were updated in thenew FMVSS 208 proposal. Dorris and Associates [72] reviewed and analysedNHTSA’s activities on airbag labels related to Human Factors Engineering (HFE) andwarning literature. The introduction of an airbag-warning standard had to balancebetween informing people on minimising possible risk and avoiding alarm that couldstop the acceptance and use of airbags. The need for occupants to be properly restrainedand positioned as a primary prevention strategy should be clear from the labels. It wasconcluded that the requirements for the labels developed by NHTSA addressed therespective injury prevention policies, responding to Human Factors Engineeringcriteria. However, current Human Factor Engineering literature is found to inadequatelymeet the needs of regulatory agencies involved in precautionary labelling.

Transport Canada suggested that the procedure described for the static out-of-positiontests for the 5th percentile female dummy may not be representative for the worst casecondition [73]. Therefore, a modified chin on hub procedure is proposed whichprioritises chest placement. The procedure also positions the steering wheel in alocation that is compatible with the visibility and comfort requirements of a 5th

percentile driver.

FMVSS 201Requirements for instrument panels, seat backs, interior compartment doors, armrestsand sun visors were specified by NHTSA in the FMVSS 201 (‘Occupant protection ininterior impact’). In 1995, the FMVSS 201U was created which also includedrequirements for a head striking pillars, side rails, headers and the roof. An update ofthe FMVSS201 in 1998 allows the presence of dynamically deployed upper-interiorhead protection systems. Advancements in testing methodologies in response to theFMVSS 201U requirements for curtain-type side airbags are studied by MGA ResearchCorporation [13]. Both airbag component testing and full scale testing (pole impact) aredescribed.

Note that the FMVSS 201 has similarities with ECE-21 head impact tests, in which arigid sphere (6,7 kg, 165 mm) impacts the IP with 6.7 m/s.

IHRA side impact working group on OOP procedures


The side airbag OOP injury technical working group (TWG) was sponsored by theAlliance of Automobile Manufacturers (Alliance), Association of InternationalAutomobile Manufacturers (AIAM), Automotive Occupant Restraints Council(AORC), and Insurance Institute for Highway Safety (IIHS). The objective was todevelop a common understanding of the risks associated with side airbag deploymentsand ways to minimize those risks. A set of recommended procedures on side airbagOOP testing was the result. The side OOP test procedures proposed by the TWG coverairbags which deploy from the door or side trim panel, the back or cushion, the roofsupport pillars or roof rail area and occupants ranging from young children to adults.

C.3 Regulations related to intelligent vehicle systems

The technology developed in the field of IVS starts to emerge but it is not foreseen to bewell implemented in the market in 5 to 10 years. Regulations actions fall in thefollowing categories• The EEVC created a new working group to study the effects of active-passive

interaction on new legislation/. The terms of reference of this group are listed below(see: www.eevc.org):− Overview of existing and future techniques and how this is coordinated by

existing organisations− Effect of these techniques on priorities for injury prevention− Effect of these techniques on existing regulations

• ISO and in particular, Technical Committee TC 22 and TC 204 activities, addressingsafety issues in the automotive field, are of particular interest for the definition of apre-crash standard.

The SARA (Short-range Automotive Radar frequency Allocation) group is an initiativetaken from commercial companies (car manufacturers, sensors providers) in which themembers wish to obtain a license for the frequency allocation at 24-GHz. Regulationsauthorities in Europe do actually not allow this frequency for automotive radarapplications. The main reason is possible interference with other applications. Themotivation for using this technology is that it will enable mass-production (costeffective) and also that the 24 GHz radar allows both large angle and near fielddetection (needed for pre-crash sensing applications).

C.4 Consumer tests: EuroNCAP

The EuroNCAP program is designed to provide a fair, meaningful and objectiveassessment of the impact performance of cars. It is intended to inform consumers, soproviding an incentive to manufacturers as well as giving credit to those who excel atoccupant and pedestrian protection [107].

EuroNCAP strongly influences car design because typically the severity levels inEuroNCAP test are higher than in regulatory tests. This results in stronger demands onthe restraint systems.

EuroNCAP ‘promotes’ introduction of new features like seat belt reminders byincluding it in their test program although these features are not necessarily included incurrent regulatory.

In Vehicle Safety[1]

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