Traffic Safety Risks with EU Tractor-Semitrailer Rigs

on Slippery Roads

Presented by Johan Granlund, WSP Sweden

Co-author: Per Thomson, Thomson Konsult AB, Sweden

Problem 1: Jack-Knife & Trailer Swing Crashes

The Tranarp Bridge in 2013.

Sweden´s largest multiple-crash ever.

First three vehicles to crash:

Jack-knifing semitrailer rigs Photo: SVT

Photo: SR

Problem 2: Jamming Icy Upgrades

Jammed upgrades:

-Risk for hazardous queue crashes.

Photo: SilverTho, Youtube

Photo: Falck

Blocked rural “lifeline roads”:

-May request hundreds of km long

detours, if alternative route even exists.

Outline

Are EU-semitrailers suitable for “outdoor use during wintertime” in the Nordic countries?

Outcome from Nordic seminar held in 2015.

The seminar revealed disproportionate risks for both traffic jams at icy upgrades and safety risks on slippery roads.

Analysing EU-semitrailer instability on icy road, using TruckSim®.

Simulation results confirm risk for jackknifing at approved winter road friction.

US Surface Transportation Assistance Act as inspiration to EU, on shifting from short COE tractors to stable conventional truck-tractors.

Research Objective and Aim of Paper

Research Objective:

• Do EU-semitrailers create disproportionate traffic jams and safety risks on slippery roads?

• If so, are these articulated vehicles suitable for “outdoor use during wintertime” in the Nordic countries?

Aim of the Paper:

Present the problem, from background to on-going work.

Nordic Seminar, held in 2015:

Traffic Safety Risks with EU-Semitrailers on Slippery Roads

The one-day open seminar was arranged by Nordic Road Association (NVF), the

insurance company Länsförsäkringar, WSP Sweden and Thomson Konsult AB.

Participants from Norway, Sweden, Finland, Denmark, Pharoe Islands and Germany.

A wrap up of the seminar outcomes is available on the NVF website.

Photo of 5th wheel top plate: D Rykkje Photo of rubbing plate at king pin: B Eklund

Outcome (1) from the Nordic Seminar:

EU-semi´s strongly overrepresented in recovery statistics over towing at slippery upgrades

Study in by Falck, Norway

Of 1780 upgrade tow actions:

33 % foreign trucks ( EU-semi´s).

Only 6 % of trucks in traffic are foreign.

Conclusion:

EU-semi´s strongly overrepresented. 0

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400

600

800

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Domestic; all truck types Foreign; almost 100 % EU semi´s

Photo: Falck

Outcome (2) from the Nordic Seminar:

EU-semi´s Multiplies Crashes w. Human Injuries Chalmers study in Sweden: +27 % crash rate per km for HGV combinations with

length 12 m - 18.75 m (including 16.5 m EU semitrailer rigs), compared to vehicle

combinations longer than 18.75 m. Longer trucks proven to be safer trucks.

Norwegian project SAFE Foreign Transportation:

Crash rates in Summer vs. Winter:

• Fairly constant for the Scandinavian truck fleet.

• Significantly increased for non-Scandinavian trucks ( EU-semi´s)

EU-semitrailers exhibit more than three times higher rate for human injuries than the

Scandinavian truck fleet on the risky mountainous road networks in Western Norway

and in the North.

Outcome (3) from the Nordic Seminar:

Impact of Vehicle Design on Risks at Slippery Roads

Critical design differences between EU-semitrailer rigs and truck with drawbar trailer:

• Few have a liftable dead axle, that can be used to increase weight on drive axle.

• Centre-of-Gravity and braking performance.

• Often high friction at articulation joint; the trailer can “take over” and decide direction.

• Short wheelbase on tractor unit.

Outcome (3) from the Nordic Seminar:

Impact of Vehicle Design on Risks at Slippery Roads (2)

Low performance in climbing steep ice-slippery hills:

- All two-axled EU-tractor units.

- Short EU-tractor with liftable tag axle (the lift affects its steering).

Disputable performance in climbing icy hills:

oShort EU-tractor w. liftable pusher axle (load´s CoG at trailer front).

oTandem drive axled truck, when unladen.

High performance in climbing icy hills:

+ Tandem drive axled truck, when laden.

+ Long bogie-axled truck with liftable tag axle (CoG in front of drive axle).

“Proposal”

Outcome (3) from the Nordic Seminar:

Impact of Vehicle Design on Risks at Slippery Roads (3)

“Surfing on snow slush”, due to pitch response of short tractor unit.

The hazardous result is loss of steering control.

Key factors include CoG, wheelbase length and 5th wheel position.

Outcome (3) from the Nordic Seminar:

Impact of Vehicle Design on Risks at Slippery Roads (4)

Why jackknifing also in T-junctions, even at parking lot speed?

Photo of 5th wheel top plate: D Rykkje Photo of rubbing plate at king pin: B Eklund

Photo: Falck Photo: Corren

• Friction at 5th wheel.

• Short wheelbase.

• Position of 5th wheel.

Vehicle Simulation Results

Legal operating speed up to 90 km/h in SE & NO.

Double lane change at approved winter road slipperiness;

friction = 0.25.

Constant speed; no braking.

Results:

• Loaded trailer jackknifed at 68 km/h.

• Unladen trailer jackknifed at 61 km/h.

Critical speed drops 10 % by unloading the trailer!

Can lowering tire air pressure on unladen trailer improve

the critical speed for jackknifing?

The animation shows unladen trailer jackknifing at 67 km/h. Acknowledgement to Mr. Mårten Johansson for TruckSim tests.

More Relevant Vehicle Simulations

Good stability of the EU-semitrailer rigs have been demonstrated in previous

simulations and tests, made on roads with high road friction.

However, EU-semi´s performance on low road friction has not been analyzed properly.

Future simulations should take into account:

• Various low road friction conditions,

including split friction in right/left wheel paths.

• Friction at the 5th wheel.

• Various tire & payload circumstances, such as type of load,

load weight, tire pressure, center of gravity positions, etc.

• Braking while making various steering maneuvers,

such as during crash avoidance.

Photo: Avesta Tidning

Inspiration from US to EU

US Surface Transportation Assistance Act (1982) formed the basis for Federal

regulation of CMV dimensions. This Act changed the law from regulating maximum

vehicle combination length, to regulating only the length of the trailers.

Without need to limit the length of truck-tractors, the predominant tractor

configuration shifted from short-wheelbase COE type, to more stable and crash

safe conventional engine-ahead-of-cab type. D. Freund at HVTT11

Photo: Smart Trucking Ph

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Summary

• Current EU-semitrailer rigs are not suitable for “outdoor use during wintertime” in the Nordic countries.

• EU semi-rigs cause disproportionate risks for both traffic jams at icy upgrades and safety risks on slippery roads.

• Novel vehicle simulation results show unacceptable risk for jackknifing with EU semi-rigs at winter road condition approved by Nordic road agencies; road friction = 0.25.

• During winter season, Nordic countries need to ban EU semi-rigs, or higher road friction (more ploughing, gritting and de-icing), or both.

• EU should take inspiration from the US Surface Transportation Assistance Act, on shifting from short COE tractors to stable conventional truck-tractors as predominant tractor configuration.

Intermediate Safety Action: Restricted Operation of EU Semi-rigs on Slippery Winter Roads

E6 freeway, South-bound for Oslo:

Due to unsafe winter road condition, particularly in Djupdalen valley, semitrailers with short two-axled truck-tractors are prohibited to pass the traffic control station at Jessheim until gritting is finished at 11 o´clock. Norwegian Public Road Administration