900368

Trajectory Analysis for Collisions InvolvingBicycles and Automobiles

ML R. “Rusty” HaightCollision Investigation and Analysis

API, Inc. San Diego, CAJerry J. Eubanks

Automobile CiDllision Cause AnalysisSan Diego, CA

ABSTRACT

Determining the impact velocity of a striking vehiclein a bicycle-involved collision is arguably the most difficultpart of preparing an analysis or reconstruction of such anevent. To help the accident reconstructionist in this effort,a series of crash tests were conducted to relate the impactvc?iobty of the striking vehicle to the throw distance for theqciist.

This series of tests was conducted using a 1984four-door Toyota Corolla and an articulated dummyastride a group of similar bicycles. The dummy/bicyclearrangement was struck at velocities ranging from 16 to2? mph (25 to 43 km/hD3) relative to the cyclist.

OFTEN, BICYCLE INVOLVED COLLISIONS are poorlydocumented in police reports or follow-up investigativereports. For example, faint tire marks made by the bicyclewhen it’s struck by a motor vehicle can be easily omitted.Even if the marks are actually visible, they’re usuallyoverlooked altogether. Further, it is difficult to establisha true “point” of impact without specialized training andan appropriate allocation of time by the investigator at thescene.

Without accurate or reliable information, it becomesan impossible task to ascertain pre-impact velocities foreii:her the striking automobile or the cyclist.

When properly gathered at-scene information is con-sidered together with the inflormation compiled as a resultof this study, the accident analyst should have a morethorough understanding of:

(1) striking velocity for the subject automobile as itrelates to throw distance D1* of the cyclist’s body,

(2) ride time ‘* for a cyclist struck by a car, and

-* Superscript notations (ie: distanceD’ or !&very et al’) referto definitions or references found at the end of the paper.

(3) post-impact movement of a cyclist’s body whenstruck by a car when the car is braking pre- andpost-impact from diYering velocities.

The testing showed that a thorough examination ofthe vehicle, bicycle, and scene is essential if one is togather sufficient information to try to determine the strik-ing velocity of a vehicle in i:his type of collision.

BACKGROUND

In 1984, a bicycle versus vehicle collision occurredin a residential intersect ion within the City of Los Angeles.A 1984 Toyota Corolla rear-ended a 26 inch (.67 m)D3lo-speed bicycle at night in a light rainfall. The partiesinvolved sought to determine the impact velocity of theToyota based on the throw distance for the cyclist.

The testing on which this paper is based wasprompted by the lack of substantial published researchon car versus bicycle collisions. Specifically, little infor-mation is currently availabl~~ regarding throw distance asit relates to striking velocity and nearly none for the ridetimeD for the struck cyclist. The goal of this research wasnot to analyze the injuries sustained relative to impactvelocity or to discover a reliable method of determiningthe impact-induced inljur)r causing movements of acyclist. Rather, this testing was done to try to determinea method of predicting an impact velocity for the strikingvehicle based on a known throw distance.

Other published work in this area has addressed thedesign of automobiles relative to prevention of injuriesand, as an aside, touched on the potential relativity ofthrow distance to impact velocity. However, none offer amethod of determining the striking vehicle’s impactvelocity based on a known throw distance for the cyclist.

A lesser goal of this study was to relate impactvelocity to the approximate center of the “head star” on

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the windshield. This study was not concerned with theseverity or degree of the damage to either the car,windshield, or dummy but rather its height and distancefrom the leading edge of the striking car itself.

TESTING PROCEDURES

The site chosen for this series of tests was a newlypaved, asphaltic concrete roadway in San Diego, Califor-nia.

Strikina Vehiclr: - For this testing, the actual Toyotainvolved in the original coillision was used. The Toyota hadnot been repaired since that original event, save for thereplacement of the windshield. A number of scratchesand gouges found on the hood of the car before testingwere identified bythe owner/driveras having been causedby the struck bicyclist’s body and belongings. The hoodarea was examined and photogiraphed prior to testing.

were attached are indicated by the arrowheads in thephoto. During testing and after reviewing the photos andvideo of the testing, it was evident that this eyebolt andleader wire arrangemIent worked properly; breaking andthen releasing the dummy virtually at the instant of impact.

There were nine tesl: runs completed during the twoday testing period. Two of the runs were conducted withthe dummy in a position that would simulate his standingat a stop sign or signal. In this series, the dummy waspositioned with one foot on the ground and the other ona pedal as though he were ready to “push off.” In theremaining seven runs, both of the dummy’s feet were onthe pedals at even heights as though the cyclist wereriding.

In the actual collision, there were two bags of miscel-laneous groceries on the, handlebars of the bicycle -. oneon each side of the handlebar stem. For six of the ninetest runs, two equally balanced bags of groceries wereattached to the bike being struck; as in the original cd-lision. The groceries in azh bag weighed 2.2 pounds (1kg).

The dummy was lalso out-f&ted with a pair of sunglas-

During the testing, the hood area was damaged bycontact with the dummy, bicycle and debris. That contactarea was examined, documented, and repainted with aquick drying flat spray paint. This provided a “fresh”surface to examine after each test run.

. .IndsQ.&& - Varying degrees of damage to thewindshield were expected in each of thevarious test runs.For this reason, additional windshields were on hand toreplace the damaged windshields between test runs.After each test run the broken windshield was removedfrom the car and a new windshield was properly re-in-stalled.

Bicvm - Since the bicycle in the original collisionwas damaged beyond repair, a set of exemplar bicycleswas obtained for the testing. While the test bikes werefrom different manufacturers, the original bike was also a“generic” brand. The group of testing bikes closely simu-lated the original bike in t#erms of size, design and equip-ment. Before each test: run, the bike seats were alladjusted and set to a height of 36 inches (0.9 m) from theground.

.yc st Dummy - The dummy used was 64 inches

(1.6 m) ti;l and weighed 70.5 pounds (32 kg) clothed in ashirt and trousers. Although the cyclist actually struck inthis collision event weighed 140 pounds (63.5 kg), safetyconsiderations for the test driver in the Toyota dictatedthe lighter, proportional dummyD4 be used.

The dummy was supported on the bicycle for testingusing eighty pound test leader wire through a loop at-tached to the dummy’s head and by the bike seat itself.The bicycle was held upright using a looped strand ofleader wire through the handlebars. These pieces ofleader wire were stretched to the breaking point betweenthe dummy and the bicycle’s handlebars and a set ofeyebolts on a wood support built for the testing.

Figure 1 shows the cyclist dummy in place before oneof the test runs. The eyebolts to which the support wires

ses. After the dummy and cycle were struck, the sunglas-ses were typically found very close to the point of impact.Studies by Severy et al’ in the mid6O’s, offered theposition that: ”. ..These 1JClA experiments have estab-lished that items of apparel and objects being carriedsuch as briefcases, purses, etc., generally are notpropelled as far as the pedestrian, in part because theytend to become dislodged from the pedestrian before he

Figure 1. The dummy/bike suspension system.

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test runs, the driver’s instructionswere I:O lock the brakes when theat-impact shot was heard. When thebrakes were applied, the second shotwould be fired.

The shot-to-shot timer wouldrecord the time between shots to oneone-hundredth of a second (.Ol set).The distance the car travelled be-tween the shots (during this knownperiod) was then measured as thedistance between the chalk marks onthe ground. When the detonatoroperated properly, the result was anaccurate finding of the vehicle’s ac-tual impact velocityD7.

During the last few test runs, thedetonator did not operate properlybecause of damage which occurredto the firing pin assembly during oneof the impacts. Nonetheless, the ac-curacy of the velocity findings maldeon those runs where both of thesesysterns operated properly werevaiidaled by a comparison of theradar observation and

Figure 2. Car mounted devices and impact strip.

is fully accelerated and, in part, because those objects areGenerally of lesser density than the pedestrian...” Theplositioning of the sung/asses after the test impacts sup-piorted the Severy et al pedestrian findings.

.er Consrderatians - Three of the nine testruns were conducted with the roadway surface dry as“control” runs. Since the original collision took place in alight rain, the remaining six test runs were conducted aftera water truck drove through the scene of the collision.

During the second day of testing, when the six ‘%vet”runs were conducted, it actually rained. Nonetheless, thewater truck passed through the scene to ensure a consis-tent testing surface for ezch test run.

.Car-Mounted Devce s - Aside from mounting the

various measuring devices described herein, no othermodifications were made to this car.

To accurately determine the impact velocity of thestriking vehicle, two systerns were employed. On everytest run, a calibrated, hand-held radar unit 5 was used todetermine the Toyota’s velocity. In addition, a secondtiming s stem using a detonator and “shot-to-shot” timingdevice Dx was installed on the front of the Toyota (seeFigure 2). This second arrangement, although arguablythe more accurate, was later damaged and proved to befunctionally unreliable from that point forward.

By design, the detonator would fire when the car’sfront bumper struck the bicycle tire and mark the pave-ment with a colored chalk mark. For seven of the nine

timer/cletonator arrangement.

During this testinghthe Toyota was also equippedwith an accelerometer . This device was down-loadedafter each run to a compu?er at the site.

On runs one and two, there was a detonator trap set25 feet (7.7 m) before the designated area of impact?The speed trap was a pai: of small pull string activatedexplosives across the intended path of the car. As theToyota was driven through the speed trap before strikingthe bike, the sound of the explosives would register withthe shot-to-shot timer and allow for a calculation of thevehicle’s average velocity through the trap area. On theremaining tests (in which t’x detonator operated proper-ly) this pre-impact speed trap was dismantled and thedistance between impacl and first application of thebrakes was the speed trap area.

In Figure 2, the timing device is visible on the left sideof the photo and indicated by the left-most arrowhead.The detonator is in the center of the photo. The impactstrip on the car is indicated by the right-most arrowheadin the photo.

The impact strip location on the bumper was selectedbased on the impact area found on the Toyota in photostaken after the original collision and on a pre-testingexamination of the unrepaired car. The impact area wasthen fitted with a tightly sprung aluminum strip whichactivated the first detonator shot as previously described.

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Photo Documentation - Several still photo andvideo cameras were used to record the testing sequence.On some of the test runs, a small video camera wasmounted inside the Toyota behind the driver to get anapproximation of a driver’s view of the collision event. Thephotos presented in this paper were taken by manuallycontrolled motor wind equipped 35mm SLR cameras atthe scene.

ANALYSIS AND DISCUSSION

While there is no argument that the results of thistesting are somewhat limited by the size of the study, thedatabase of information can be generally applied to col-lisions involving impact velocities between 15 and 30 mphinvolving pontoon and wedge shaped vehicles.

A comparison of this data to other previously publish-ed works shows that this body of data would mostprobably apply to highler impact velocities as well asimpacts from different a,ngles providing that the cyclistwas projected from the tar after impact.

Huij bers2 pointed out: “The dummy and cadaverexperiments show that vehicle impact velocity has a con-siderable influence on the throwing distance of the cyclistand bicycle. The vehicle stiffness and vehicle geometryappear to have minor influence. Impact direction hardlyeffects the throwing distances.”

Otte3 addressed direction of impact and classifiedthe relationship between the striking/struck car with thatof the bicycle into seven collision profiles. While Otte3specifically addressed injury relative to the collision profiletype, he grouped the throw distances (regardless of thestriking velocity) into one set of findings as shown inFigure 4.

In analyzing the test database from this series ofcollisions, an analysis has been made of the throw andslide friction coefficients ‘to further validate the use of thelighter dummy through a comparison to previous works.Throw distance friction coefficients calculated by Becke4,Searle5, and Schmidt’ vary from .6 to .7 values. In ourse&x of tests, the throw distance coefficients variedbetween .23 and .47.

While the throw distance values found as a result ofthis project are somewhat different from those found inthe cited works, one should note that in those references,the values were representative of pedestrian impactstudies whereas our testing was done with a rider/bicycleconfiguration with a higher pre-impact center of mass. Apedestrian’s center of m,ass is considerably lower thanthat of a cyclist astride a bicyclle. For that reason, thecyclist will be carried higher onto the windshield thanwould the pedestrian struck at the same velocity. Addi-tionally, time is consumed during collapse of the rear tireas it is struck by the car. The resultant final throw distanceis compounded because, during that additional time, thecar moves and carries the cycle some additional distance.

Consideration was also given to the slide distancefriction coefficient. The works by Severy et al’ and Collinset al7 calculated friction coefficient values for slidingbodies. Using slide distances only, their coefficientvalues are between .#8 and 1.2. In the series of cyclist testsdiscussed herein, the friction coefficients for slide dis-tance only were beWeen .8 and .95? Clearly, this fellwithin the range of previous findings outlined in the citedsources1’7. Based on this information it is clear the lighterdummy, when in contact with the ground, had essentiallythe same friction coeffic:ient as a heavier cadaver and/orHybrid Ill-type dummy.

The dummy used in this testing was lighter than thehuman involved in the actual collision itself and lighterthan a Part 572,5Oth percentile dummy. It is the positionof the authors that the difference in weight had no bearingon the information being sought when the project was firstconceived in as much as gravity has the same effect ona 70 pound (32 kg) body as it would on a 140 pound (63.5kg) body. The force of gravity on a free falling or slidingobject is constant with respect to weight. A measure ofsupport for this position is seen in a comparison of thethrow and slide coefficients shown in Figure 3. Figure 3 isa graphic representation? of the high and low values forthe friction coefficients lound in the cited works’*2*4151617and those found as a re:;ult of this particular testing.

In the final analysis, our findings and comparisonsnot only validated the use of the lighter dummy as yieldingreliable data but also provided us with additional informa-tion regarding the friction coefficient for a body sliding onthe ground.

In the Otte3 study, the author compiled the data from614 real-life collisions investigated by a research team inGermany. In these collisions, the research teams docu-mented the throw distance of the involved cyclists. Otte3wrote: ‘The throwing distances of cyclists are similar to

14

121

0806

0.4

020

Low tbrowHigh throwLow slideHigh slide

Becke Searle Schmidt S e v e r y

0 6 066 0 70 7 066 07

0812

m Low throb+ m H\Qh throw EEILOW slide F§ilHlQtl slide

Morris HuijbersThls test

041 0 230 7 0 4 7

08 081.2 0.95

Figure 3. Friction coefficient comparisions.

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<those of pedestrians, i.e. speed-depending within aoarable-shaped exceptiIon region...Throwing-up a n daway distances of cyclists as well as of two-wheelers offerpossibilities for the determination of speed values.”

Although not providing a method for such velocitydetermination, the Otte3 study supplied information aboutIhe throw distance of the cyclist (notably grouped bycyclist’s height rather than weight) relative to the impactvelocity of the striking vehicle. Figure 4 includes a plot ofthe Otte3 throw distance information. The Otte3 paper’sreal-life cyclist’s throw distance figures include all but thehighest velocity run’s data, point from this testing. This isanother indication that thle lighter dummy very closelysimulated the movements of full-size human cyclists fromimpact to rest that were documented in some 614 real-lifecollisions.

In another example, Wood et al8 calculated a throwdistance/impact velocity curve for both a rider and bicyclebased on real-life collision investigations. In Figure 4, thecurve (reflecting the area between the 97.5’h and ~?.5’~percentile of cyclists) has been compared to the resultsof this study as well as the Otte3 data. In the graph, theWood’ curve more narrowly limits the predictable rangeG! throw distances relative to the impact velocity. Thec’ata from these tests conducted with the lighter dummfit the even more narrow projection seen in the Wood ii

Strl klng Speed (km/h)

study which itself fiis witqin the more broad Otte3 datapoints.

A third comparison might be made to mathematicalmodeling such as is described in HuijbersJansseng.HuijbersJanssen’sg calculations of the throw distancefrom mathematical mod&ng using a MADYMO 3D cyclistmodel (dummy validated, version 4.1) based on results ofcadaver-cyclist testing1 was done primarily to determinethe influence of car design on injury to the cyclists.

Their work cited tlhrow distance as impact veiocity-dependent and, as with the other examples cited, did notaddress the weight of the cyclist. The HuijbersJanssengtesting was based on aI modified Part 572 50th percentiledummy. In fact, those models were of a cyclist-bicyclesingle mass unit and were classed by riding position(seated upright versus racing position) rather than evengross weight of the two as a unit, direction of impact orimpact velocity. Huijbe!rs-.Jansseng wrote: “In the simula-tions the bicycle was represented by a rigid mass with amass distribution identical to the bicycle in the dummyexperiments. In one of the simulations, the bicycle masswas decreased by 50016. The effect of this was a slightdecrease of all peak values of about lOoA or less.”

The HuijbersJansseng work is also shown in Figure4. The data points from the mathematical models fit intothe area shown by the two previous works cited (Otte3

40

0 2 4 6 8 IO 12 14 16 18 20 22 24 26 28Throw Dletance (m)

0 Huljbers

- otte

-x-- Wood 2.6% + Wood 87.6% * Halght/Eubanks

- otte 0 INRETS t e s t s

Figure 4. Comparison of throw distances with cited works.

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and Wood et al’) and com-pare favorably with thedata points found in thisstudy using the lighterdummy.

Clearly, that the actualand predictable trajectoryand slide behavior of thedummy in this testing fellwithin the parameters of (1)the real-world expecta-tions, (2) the dummy andcadaver testing throwpredictions and (3) themathematical modelingshould be sufficient to sup-port the position that thelighter dummy providedaccurate and reliablethrow and slide distance in-formation relative to strik-ing velocity.

A f u l l y w e i g h t e ddummy may well havegiven a more aciurate rep-

Figure 5

resentation of the severity of the damage to the car andthe actual or predictable physical injuries (chest load, etc)that the cyclist might sustain in such an impact. However,the foremost concern in ‘this regard was for the safety ofthe test driver of the Toyota. Further, the goal of thistesting was nat to determine what injuries the cyclistwould have experienced, but rather what would havehappened to the cyclist’s body as a single mass undervarying conditions such as velocity and rider position.

Otte3 and HuijbersJansseng address the relation-ship between striking velocity and the “ladling up” or‘Throwing-up” effect on the cyclist. Both discuss meas-urements for head impact points back onto the hood andwindshield area of the vehicles and that distance’srelationship to impact velocity. Otte3 wrote specificallyabout this: “only an influence of the body size and impactvelocity was observed. Children impact the center of thefront hood more frequently, due to shorter throwing-updistances. Adults, however more often impact the rear ofthe front hood as well as the windscreen. But the maininfluence must be seen in the collision velocity. Shorterthrowing distances were observed in connection withlower rather than higher impact speeds...” Otte was ex-plicitly suggesting that the height (and thus the center ofmass) of the cyclist was nearly of equal importance as thestriking velocity and apparently gave no concern to theweights of the riders.

Huijbers-Jansseng wrote: ‘The impact speed of thecar influences the longitudinal impact location and rela-tive impact velocity of the head...”

Photo of the movement of the dummy onto the car

With the qualification that the cyclist’s body didn’tbreak the windshield when he started in a “standing”position as in runs eight and nine, there is some com-parison that can be made of the striking vehicle’s velocityversus the cyclist’s movement to windshield/“A” pil-lar/roofline area.

While no accurate velocity estimates can be madewith this information alone, some questions can beanswered by an analysis of the location of the center ofthe damage or “head star” on the windshield as an indica-tion of the movement of the cyclist’s body.

From this and other studies8’g*‘0 the higher the im-pact or striking velocity of the car in the cdlision, thefurther back toward the windshield from the front of thecar the cyclist or pedestrian’s body will be carried.

In the HuijbersJans:;eng paper, the authors describethe effect of the striking vlehicle’s impact velocity resultingin “the movement of the cyclist into the windscreen.” Thatresult was described as t ‘le “lethalityg” of the cdlision. Assuch effect relates to this testing, Huijbers* indicated thata rear impact collision had a much higher “lethalit)/’ thanother types of bicycle inl/dved cdlisions. The Huijbers-Jansseng paper cited testing done with cadavers as weilas mathematical moclels and discusses the effect of dif-ferent automotive nose c esigns.

Their paper outlines what is described as a hypotheti-cal “Safe 90” vehicle model. They noted, “this ‘Safe 90’was chosen in such a. way that it was estimated that thiscar will probably be safe too (sic) for pedestrians andcyclists in case of a collision.”

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Figure 6. Photo of the dummy being thrown-up onto the car

In our particular set of tests, the cyclist was carriedonto the hood of the car and struck the lower portion ofthe windshield - at or below the midpoint of the windshield- at velocities between 15-20 mph (24-32 km/h). Wherethe cyclist was astride the cycle as if he were standing andonly one foot was on the pedals, the center of the impactdamage to the windshield was at or below the base of thewindshield itself.

At velocities between 20-25 mph (3240 km/h), thecenter of the impact area seen on the windshield is foundat and above the vertical center of the windshield. Forimpacts above that velocity, the center of the impact areais found more toward the top of the windshield and ontothe roof at the leading edge of the roof line.

The movement to the windshield by the dummy isshown more graphically in Figures 5 and 6. Figure 5 is aview of the impact in run number five where the impactvelocity was 20.7 mph (33 km/h). In this photo, one cansee the car moving “under” the cyclist as the impactprogresses. The photo shows how the cyclist’s highercenter of mass (compared to that of a pedestrian) wouldmake the throwing-up onto the hood “easier” for thecyclist at a lower impact velocity. The central differenceseems to be that the pedestrian’s center of mass ist!lpically lower than that of the cyclist and nearer the upperleading edge of the front hood while the cyclist’s centerof mass starts out weil above that point.

The question becomes: if the dummy had been moreheavily weighted, would there have been a difference in

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the dummy’s rate of fall to i:he hood of the car or a greaterdrag and/or damage to the hood of the car from thisgreater weight? It is our position that it would not.

As stated earlier, the actual damage to the hood ofthe car caused by the 140 pound cyclist struck in thelitigated case was documented before the testing. Ontest number one, we foLind scratches caused by thedummy virtually overlapping the pre-existing “real-world”scratches and gouges on the hood. Finding that samepre-existing damage Inearly duplicated by the lighterdummy in this series of tests and would clearly lead to theconclusion that the weight is insignificant for the impactinduced movement of t:he dummy during the impact.

Otte3 provided a chart showing the impact positionsfor his riders at velocities LIP to 31 mph (50 km/h). Figure7 shows the impact poGtions on the hood/windshield inthis set of tests relative to those plotted by Otte3. Themajority of the points plotted in the Otte3 paper arecentered on the striking vehicle whereas those from thistesting set are offset to the driver’s side of the car. Theinitial contact areas between the bicycle and the vehiclesinvolved in the collisions documented by Otte3 are anunknown whereas, in this testing, the cycle was intention-ally positioned to the driver’s side of the striking vehicle.

The difference in positioning or “throwing -up” dis-tance can be seen in a comparison of Figures 8 and 9. InFigure 8, from test run number seven where the impactwas 18.6 mph (29 km/h), the cyclist is carried through the

5;*2 *

l*

)) )

))

* = Otte d a t a> = HalgWEubanks d a t a

Figure 7. Ladeling-up positions on the striking car.

impact with the windshield and then “ladled-up” onto theroof of the car before leaving the car off the driver’s side.

In Figure 9, a photo <from run number four where theimpact velocity was 27.5 mph (44 km/h), the cyclist is seenat the point of impact with the windshield. The center ofthe windshield damage is at the dummy’s shoulders at thetop of the windshield and onto the leading edge of the roofline where the head has already struck and hadrebounded before this photo was taken. Note the posi-tion of the sunglasses in this photo (Figure 9). Unlike whatis shown in Figure 8, where the impact velocity was lower,

the dummy travelled ‘onto the roof and exited the car fromthe roof rather than being “ramped” up the front of thewindshield and off the side at the “A” Pillar.

Although it is our position that some limited estima-tion of an impact velocity might be made based on theheight of the center of impact damage on the windshieldof the striking car, a great deaf of consideration should begiven to any estimations of velocity based solely on theactions of the cyclist’s body on the striking car as a resultof the impact.

Another consideration is that no finding of velocitycan be based sdefy ton aa lacrk of windshield damage. Intest runs eight and nine, 1 he impact velocities were 17 and21 mph (28 and 34 km/h) and the windshield was nntbroken. In these two te.st runs, the cyclist was standingwith one foot on the ground and the probability would bethat he would have sulfered significant sacral injuriesbecause of contact with the bicycle saddle. In short, theinjuries to the cyclist should always be compared to thedamage to the car and bicycle before even the mostlimited velocity estimate can be rendered. To assumethat a lack of windshield damage indicates a velocitybelow some given figure based solely on that lack ofdamage is not s~pp~orted by the database of this testseries.

Aside from the post impact movement of the dummyinto the windshield, the cyclist’s movement on the groundto rest was also largely predictable. In this testing, with

Figure 8.

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one exception, whenever the dummy was astride thecycle as though he were riding, the dummy’s post-impactposition relative to the car’s at rest position was predict-able.

When the front of the car dipped under brakingapplication before impact, the rider was projected aheadof the car and came to rest further from the point of impactthan the car did. When the car was not braking at impact,and when the rider is astride the cycle as though ridingand not standing, the cyclist is thrown off the side of thecar after being ramped back onto the windshield. Thiswas not the case in test run five.

As shown in Figure IO, from run number five, thedummy was projected back onto the hood and into thewindshield as in the other test runs; however, this time,the “skin” on the back of t:he dummy’s head caught theseam at the roof line and top of the windshield. Theclummy “hung up” on the wiindshield/roof line long enought3 be slowed as the car was slowing and was then castfl3rward as the car continued to slow to a stop.

It is our position that, generally, the point of rest oftie cyclist relative to the car’s point of rest is one indica-t on of the car’s braking attitude at impact.

As with any other aspect of r;ollision analysis, careshould be given to making absolute statements. Noopinion with respect to the pre-impact braking attitude ofthe striking car can be rendered based solely on the atrest position of the cyclist’s body relative to the car after

the collision. A thorough examination of the damage tothe car and the injuries to the cyclist should be carefullyconsidered before offering any opinion regarding thestriking vehicle’s actions’ pre-impact. Further, a sig-nificant finding of pre-impact skid marks should never becast aside based on a Finding of the cyclist at rest in frontof the car’s at rest position.

The issue of the sunglasses and their point of restrelat’we to the point of impact was not a primary area offocus when the goals for this study were laid out. None-theless, information from the previous study cited(Sever+) that 1’. ..items of apparel and objects being car-ried...“and Otte3 that some lighter debris would often landnear the point of impact was significant enough that someportion of this test was devoted to providing additionalinformation in this area.

Otte3 wrote: “Shopping bags attached to the bicyclemark the collision place, lhis is especially the case withliquid containers...”

Based on our work with this set of tests and a reviewof the Otte3 and Severy’ studies, there is some value tothe finding and documentation of light apparel or personalbelongings at a pedestriin or bicycle collision scene.

At the same time, no single point of impact can bedetermined based solely on the finding of these items ata certain location at the scene, but it may be helpful infinding the area where the collision occurred. Any deter-mination or finding of the location of impact using articles

Figure 9.

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Figure 10.

worn by the cyclist should be reported as part of an “areaof impactD”” rather than the more specific “point” ofimpact.

Figure 11 is a graphic showing of the distance theglasses were found relative to the point of impact. Exceptwhere the glasses stayed with the cyclist for an extendedperiod of time, the glasses came to rest within about 4.5feet (1.4 m) of the point of impact. When the glassesstayed with the dummy, even for a short period or wereinvolved in a secondary or subsequent impact with thedummy or car, they were moved much further from thepoint of impact. This was seen in runs seven and eight ofthe test set as reflected in Figure 11 and the attachedappendices.

Based on the information obtained in this study,neither the area over which the grocery debris is spreadnor distance that the furthest pieces were thrown can beequated to the velocity of the striking vehicle. Thegroceries, in this type of impact, were dispersed as shownin the drawings (Appendix C) as indicated for each of thesix test runs where groceries were attached to the cycle.

Secondary or tertiac/ impacts between the groceryitems and each other in and out of the grocery bags, orwith the groceries and the car or dummy, each affectedthe direction and distance an individual piece of debriswas carried. For example, after ihitting the ground, someitems, such as soft drink cans, rolled with the crown of theroad.

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Wood et al8 and Otte3 discussed the potential valueof the bicycle’s throw distance in making a velocity deter-mination. In this research, consideration was also givento the post impact movement of the bicycle as it relatedto the impact velocity.

On one of the test runs, the bicycle caught under thefront of the car to its at rest position. On three of the runs,the cycle was pushed by’the car while it was caught underthe front bumper, but released as the car came to rest.On those three runs, the cycle came to rest in front of thecar’s at rest position. On yet another test run, the caractually ran over the bicycle and essentially stopped thecycle at that position.

For the remaining iour test runs where the cyclemoved clear of the car, the friction coefficient for the cyclealone was found to be between .6 and .8. Even lookingat this smaller database, the high figure represents a testrun where the cycle and 1:he rider stayed together to rest.Using the information obtained by measuring the tiresboth for maximum deformation and to find the total of thetire area lost to the impac:t damage, we found no correfa-tion between such damage and the velocity of the strikingvehicle.

Figure 12 is a photo taken of the damage to one ofthe tires used in this testing. At the very least, additionaltesting regarding bicycle tire make up, spoke positioning,the age of the tire, and th+ rim assembly would be neces-sary to lead researchers ‘toward some method of making

Distance (11)

18.8 27.5 20.7Impact Velocity (mph) CONCLUSION

m Glasses ea Based on the information from this study and withinthe limitations previously described, one can predict, withsome degree of reliability, the velocity of a striking car ifthe throw distance of the cyclist body is known. Inanalyzing the data set for study, three linear regressionswere completed from the information gathered. In addi-tion, the data set was compared against the product of aformula to calculate the approximate velocity for an objectthrown.

Figure 11. Sunglass movement, post collision distances.

a comparison of the vtdocity and damage. In Figure 12,the arrow indicates the direction from which the tire wasstruck.

Because the cycle interacts so extensively with thefront of the car, it is our position that no direct inferencecan be drawn as to thIe friction coefficient for the slidingbicycle based on the current state of the informationavailable in these tests.

Ride time for the cyclist on the car was not discussedin any other cited treatments of this subject. Based onthe findings from these nine test runs, the ride time for thecyclist struck in this manner at velocities between 15 and30 mph (24 and 48 km/h) is, on the average, 1.3 seconds.

On run number ttio, where the brakes were appliedbefore impact and the dummy had to travel both back andforth across the hood, the ride time was a high of 1.5seconds. The majority of the ride times were 1.4 secondsin duration although some were as short as 1 .l seconds.Figure 13 shows the ride times relative to each of the testruns.

Figure 12.

Figure 14 is a ch,art showing the throw distance toimpact velocity for each of the nine runs in this test. Theprojections of each 01’ the three linear regressions havebeen drawn through the graph in Figure 14.

The first data set analyzed was a compilation of allthe impact velocities and the corresponding throw distan-ces. Using that data set, the following regression equa-tion was devefopcd for the determination of velocitybased on throw distance. The metric equivalent informa-

tion is available in Append’ix B - Metric.

Veto&y = DistanctP l (X coef) + constantor velocity, in mph, is: V=S*.158+ 13.141

For example, where the distanceis 2!j feet (7.7 m), the impact velocityvvould be approximately 17.0 mph(27.:3 km/h).

The second linear regressionmed the same data set but exdudedthe velocity and throw distance for runnumber 4. Run number four might beconsidered the “high end” run inas-muchas the impact velocitywas 6 mph(‘9.6 km/h) greater than the nexthighest run velocity.

Using the data set for the remain-ing runs, the following regressionequation was developed:

Velocity = DistanceR l (X coe~f) + constantor velocity, in mph, is: V= S.098 + 15.367

For example, where the distanceis 25 feet (7.7 m), the impact velocitywould be approximately 17.8 mph(28.6 km/h).

153

18 4 19.6 27.5 20.7 l&Q 113.6 17.5 21.3

Impact Velocity (mph)

m Ride Time,

Figure 13. Ride time chart.

The third linear regression excluded the data pairsfrom runs two, three and eight. On runs two and three,the braking was pre-impact. On the remaining runs, thebraking was post-impact sothesetwo runs were excludedfrom this regression on that basis. On run eight, thebraking was post-impact; however,, on this run the cyclistwas standing with one foot on the ground rather thanstarting out in a riding position on the bicycle. While thesame was true for run nine, two points distinguish runeight from run nine.

Another analysis can be made for the impact velocityof the striking vehicle based on throw distance and throwdistance effective drag lactor or friction coefficient for thecyclist’s body. The fornnula for the approximate velocityof an object thrown is shown as Figure 15. The formulashown as Figure 15 has been applied to the throw distan-ces for the nine test runs in this database using the throwaverage friction coefficient of .33 and a level take off anglefrom the windshield and/or hood area. The results of thiscalculation have been compared in Figure 16 to thevelocity calculations made using the formula derived fromthe linear regression previously discussed.

First, on run eight, the seat broke and the dummymoved free of the cycle to its at rest position. Second,the velocity for run eight was 17.5 rnph (28.2 km/h) whilethe velocity for run nine was 21.3 mph (34.3 km/h). The

Using the formula shown as Figure 15 with theaverage throw distance coefficient of friction and the leveltake off in this type of cdlision, the formula predicts aimpact velocity an average of 1.5% higher than actual

DIS-MNCE (ft)

a86

86

76

05 li65

45

35

26

16 -18 17 18 18 20 21 22 23 24 26 28 27 28

VELOCITY (mph)

nearly 5 mph (8 km/h) difference was significant enoughto project the cyclist and bicycle with which he becametangled much further onto the hood of the striking car.Because the cyclist was carried up to the base of thewindshield, this test run was more like the lower velocityruns considered as the rernainder of the data set for theregression equation. Using the data set for the remainingsix runs (including run nine), the fdlowing regressionequation was developed:

Velocity = DistancG l (X coef) + constantor velocity, in mph, is: V= S*.203+ 10.314

For example, where the distance is 25 feet (7.7 m),the impact velocity would be approximately 15.4 mph(24.7 km/h).

K

* rN3tance/Veloclty + Reg’sn All Rune

-ff- fleg’sn w/o Run 4 * Reg’an w/o 2 , 3, 8

Figure 14. Linear regression chart.

154

V = Velocity (fps) S = Distancemu = Coefficient of friction fl = Angle

Figure 15

impact velocity for these tests. In Figure 16 there is asignificant difference between the calculated and actualtest velocities on runs two and three. The calculatedvelocity is less than the actual impact velocity of the twotest runs. Without offering other explanations for thisvaried result, we would point out that, on runs two andthree, the driver applied *the brakes before impact.

The higher calcula&d velocity found on run eightmight be compared to a calculation for the velocity of apedestrian rather than theat for a cyclist. In the eighth run,the cyclist was standing lower than on the previous runsand the center of mass was thus correspondingly lower.While this was also true for the final run (run nine), thevelocity in run nine was higher than run eight and thecyclist moved higher on the hood of the car than in theprevious run. The movement higher on the hood in runnine produced a reaction more in line with the previoustest runs and, accordingly, a result more consistent withthe remaining test data sets.

In addition, the cyclist body stayed in contact withthe bicycle throughout the post-collision sequence all theway to rest on run nine <whereas they separated on runnumber eight.

The formula for the approximate velocity of an objectthrown (Figure 15) would seem to provide adequateresults based on the current data set and might be usedwith some reliability given a similar set of facts as in thetest database.

The importance of the at-scene investigator locating,properly identifying and documenting the point or area ofimpact as well as the point of rest for the cyclist cannotbe stressed strongly enough. The accuracy of identifica-tion of roadway markings, items attributable to the givencollision and thorough al-scene documentation are cru-cial to the reliability of any velocity estimate using this orany other database.

Direction of Future Resmrch

Future research in this field should include a largersampling of velocities - particularly those above 30 mph(48 km/h), different types of vehicles, and various relativepositioning between the striking car and bicycle such ascollisions involving a perpendicular approach by the strik-ing vehicle.

Additionally, specialized training for accident inves-tigators and analysts should include proper identificationof the faint tire marks left by the struck bicycle as well asmarks left by the striking car as well as correct identifica-tion and documentation of other evidence found at thescene.

More and more Americans are killed or seriouslyinjured each year in traflic cdlisions than any other typeof accident. Improved administration of accident inves-tigation training programs and the appropriate allocationof manpower are the most necessary elements of anygovernment agency’s response to traffic cdlisions withintheir particular jurisdiction. Suitable attention by publicofficials can only result in a more exacting identification,documentation and cdlt?ction of evidence and sewe toproduce a more precise analysis of a given cdlision event.

Impact Veloctty (mph)30

25

20

15

10

5

0

Bim

2 3 4 5 6 0 9

FormulaTestRegression

228 15 .4 16.7 28.5 22 4 17.2 18.8 2 0 . 7 2 2 . 421 18 4 19 6 2 7 5 2 0 7 16.9 18 6 17 5 21.3

21 1 15 2 16.1 27.1 20 7 16.4 17.6 19.1 20.7

B Formula I- Test m Regress ionA

Figure 16. Comparison of actual and predicted values.

155

Clefinitions

Dl. The “throw distance” is the distance from thepoint of impact to the m, uncontrolled point of rest forthe cyclist. The entire distance including any portionsspent on the striking vehicle or in the air are included inthe “throw distance.” The throw distance includes the“slide distance” which is the distance the body travels ptlum as it comes to rest. See Figure 17.

D2. The “ride time” as used in this narrative is thatperiod of time starting when the bumper of the strikingvlzhicle impacts the tire of the bicycle and ending whenthe cyclist body strikes the ground.

D3. Throughout this narrative, the metric conversionswill be truncated.

D4. The term “proportional mass,” for purposes ofthis paper, is used to mean that the body part weights ofthe dummy were proportionally equal to the body partw!eights of a human. This dummy was not a standardHybrid III dummy. There was no simulation of rib/chests\:iffness nor joint stiffness or flexibility capable with thisparticular dummy and no such flexibility nor restriction offlexibility was necessary to achieve the intended goals ofthis testing.

05. The radar unit used in this testing was a Decaturmodel Gl Ragun. It was calibrated before the testing eachday with a tuning fork at 65 mph and with its own internalcalibration features. The radar unit reads velocities to onetenth (.l) of a mile per hour. The radar unit was ap-proximately 100 feet (30.5 m) from the point of impact andparallel to the path of the Toyota.

D6. The shot-to-shot timing device was a PACT MKII Timer and chronograph. This device, designed primari-ly for use at “combat” pistd matches measures the timebetween gunshots to one one-hundredth of a second(.Ol). The detonator was the standard two shot 25 calibrecclalk shot skid test detonator.

07. The velocity of the vehicle through the trap dis-tance is equal to the distance between the chalk marksfound on the ground divided by the time between shotsfired by the detonator. For use in this study, the impactvelocity used for the regression calculations as well as forother comparisons and the attached appendix was theradar measured velocity for the car at im. Thatvelocity was adjusted in runs two and three to account forslowing during pre-impact braking.

D8. A G-Analyst accelerometer manufactured byValentine Research, calibrated to the Toyota at the sceneprior to testing each day, was mounted in the car. Thisdevice reveals acceleration values in one tenth (.l set) ofa second increments.

D9. The actual slide distance drag coefficient valueswere between .8 and 9.4 for the complete series of testruns. The two values for the test runs where brakingoccurred before impact should be discarded because the

dummy stayed on the hood of the car virtually until thecar came to rest. This caused the dummy’s slide distanceto be lessened considerably and produced an artificiallyhigh figure. On test run number 2, the coefficient was 9.4.On test run number 3, the figure was 1.22 for the frictioncoefficient. While the ‘I .22 figure fell within the range ofthe works cited, the d$a was not included in the narrativebecause the braking was pre-impact causing a ridedownvelocity on the rider exiting the vehicle.

Dl 0. “Area of impact’ is a non-specific area on theroadway, as opposed to the more specific “point” ofimpact. “Area of impact” should be used where limited orno physical evidence is available or documented to posi-tion or determine the exact “point” of impact.

Figure 17. Throw distance vs slide distance.

15614

1. Sever-y, Derwyn and Brink, Harrison (1966). AutoPedestrian Collision Experiments, Institute of Transporta-tion and Traffic Engineering, Department of Engineering,University of California at Los Angeles, also SAE (Societyof Automotive Engineers) Paper number 660080.

2. Huijbers, J. J. W. (1984) A Description of Bicycleand Moped Rider Accidents Aimed to Indicate Prioritiesfor injury Prevention Research. IROCOBI, Delft, Nether-lands.

3. Otte, D. (1989) Injury Mechanism and CrashKinematic of Cyclists in ,4ccidents - An Analysis of RealAccidents, SAE 892425.

4. Becke, M. and Golder, U. (1986). Rutschweiten vonFussgangern urf nasser Fahrbahn (Sliding distances ofPedestrians on Wet Roads,) Verkehrs-unfall undFahrzeugtechnik, December 1986, Heft 12.

5. Searie, J. A. and Searle, A. (1983). The Trajectoriesof Pedestrians, Motorcycles, Motorcyclists etc followinga Road Accidents. Proceedings 27th Stapp Car CrashConference, SAE, Page 2177.

6. Schmidt, D. N. and Nagel, D. A. (1971). Pedestrianimpact case study. Proceedings 15th Conference As-sociation for Automotive Medicine.

1. Barzelay, M. E. and Lacy, G. W. (1982). Chapter1 5 , P e r s o n a l MGcientific Awile A -.mI Matthew Bender Publishing.

2. Grosch, L. and Hochgeschwender, J. (1989). Ex-perimental Simulation 01’ Car/Pedestrian and Car/CyclistCollisions and Application of Findings in Safety Featureson the Vehicles. Sociiety of Automotive Engineers (SAE)paper 890751, SAE Publication SP-782 &&motive Fmv, SAE Publications Division.

3. Severy, Derwyn and Brink, Harrison (1966). Auto-Pedestrian Collision Experiments, Institute of Transporta-tion and Traffic Engineering, Department of Engineering,University of California at Los Angeles, SAE paper 660080.

4. Kuperstein, I.S. and Salters, N. L. (1988) Chapter,50, Attorneys Guide To Enaineerina. Matthew Bender

Publishing

5. Dorsch, Margaret M., Woodward, Alistar J., Some-rs, Ronald L (1984) Effect of Helmet Use in ReducingHead Injury in Bicycle Accident, ADAM, 28th Proceed-ings.

6. Searle, John A., Searfe, Angela, The Trajectoriesof Pedestrkxs, Motorcycle and Motorcyclists, etc. Fol-lowing a Road Accident, SAE 831622.

7. Eubanks, Jerry J , Pedestrian Collisions: A For-mula to Determine Vehicle Speed based on thePedestrian’s Travel Distance from Impact to Point of Rest,(1988) IMRS Conference, (1989) SOAR/WATAI Con-ference, (1989) TAARS Conference.

7. Collins, James C. and Morris, Joe L and Collins,. . .Accident Reconstruction, Hi&,!av Callrslnn AnalystsThomas Publishing.

8. Wood, D. P. and Riordain, S. 0. (1989) ImpactSpeed From Bicycle, Motorcycle and Rider Throw Dis-. ,. . .t a n c e . Proceedings of the Can&an Mq[Safetv, University of New Brunswick.

9. Huijbers, J. J. W. and Janssen, E. G.(1988). Ex-oerimental and Mathematical Car-Bicycle CollisionSimulations, SAE 88 1726.

10. Snyder, Greth and Eubanks, Jerry J. (1986).Pedestrian impact and Trauma Analysis, lecture to SATAI(Southwest Association of Technical Accident Inves-tigators), January 1986.

157

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1627

Trajectory Analysis for Collisions Involving Bicycles and1 AutomobilesAppendix C

Diagrams of the post-impact resting positions of the cycle, dummy, vehicle and debris.

l

-

k

Appendix C, Figure 1, test run number 1. Appendix C, Figure 2, test run number 2.

Appendix C, Figure 3, test run number 3. Appendix C, Figure 4, test run number 4.

Appendix C, Figure 5, test run number 5.

..

:a X

Appendix C, Figure 6, test run number 6.

160

Trajectory Analysis for Collisions Involving Bicycles and AutomobilesAppendix C

Diagrams of the post-impact resting positions of the cycle, durnmy, vehicle and debris.

Appendix C, Figure 7, test run number 7. Appendix C, Fiigure 8, test run number 8.

Appendix C, Figure 9, test run number 9.

Appendix C, legend for characters used in this appendix.

161