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Thought Leaders

 
 

I denna bloggen kan du följa våra Thought Leaders. Det är medarbetare som var och en ligger i framkant inom sitt kompetensområde och som gärna delar med sig av sin kunskap.

 
 

Why articulated heavy vehicles are hazardous on Nordic highways

7 december, 2016
 

WSP Parsons Brinckerhoff explains why the short European truck-tractor (prime mover) has significantly higher crash rate than up to 25.25 m long rigid truck with drawbar trailer on ice slippery Nordic roads during the winter season. We also propose how to solve this serious traffic safety issue, both by improving the EU vehicle regulations and by raising the standard for winter road slipperiness in the Nordic countries.

 

Heavy goods vehicles (HGV) for long haulage within the EU Nordic countries have due to regional evolution mostly been straight trucks with drawbar trailers. In the past decade, there has been a significant increase in articulated EU tractor/semitrailer rigs within the Nordic countries, a trend driven by lower freight costs when using low paid drivers from Eastern Europe. Heavy trucks are often involved in crashes and traffic jams on ice-slippery winter roads. An ever-increasing number of voices are stating that the articulated vehicles present disproportionate high traffic safety risks on icy winter roads. WSP Sweden and Thomson Konsult AB have opened a discussion on some regulatory factors ans design factors that partially explain why EU semitrailer rigs are particularly associated with jamming long steep icy upgrades, and with loss-of-control crashes such as jackknifing and trailer swing. A novel analysis was made with TruckSim software. The results support the opinion that EU semitrailer rigs are an unsafe vehicle combination on slippery roads. This finding calls for deeper research about the winter road safety risks with the EU tractor/semitrailer vehicle combination, as well as on how to mitigate its safety risks. Results from such research are likely to be useful arguments for modifying the EU directive 96/53/EC, so that tractor units with longer wheelbase can be used without conflict on trailer length and payload volume. USA may serve as inspiration to EU on this matter, with the 1982 Surface Transportation Assistance Act. This act formed the basis for Federal regulation of CMV dimensions. The 1982 act changed the law from regulating maximum vehicle length to regulating only the length of the trailers. Because it was no longer necessary to limit the length of truck-tractors, the predominant tractor configuration in the US shifted from the short-wheelbase cab-over-engine type to the conventional engine ahead of the cab type. This has reduced crash frequency for articulated vehicles in the US. EU is encouraged to implement similar regulations in order to reduce the semitrailer rig crash frequency, particularly on icy winter road surfaces in the Nordic countries.

A series of computer-aided simulations have been made of the behaviour of EU-semitrailer rigs on winter-slippery road surfaces with friction coefficient 0.25 (approved slipperiness for all state highways in Sweden at road temperatures below -12C). The results for a double lane change show that with unladen trailer the critical vehicle speed for jackknife crashing is as low as 61 km/h. With full laden trailer the critical speed is raised by more than 10 % and reaches 68 km/h; still a low speed far below a reasonable safety margin. Our animation of an EU-semitrailer rig with unladen trailer, making a dual lane change at 67 km/h on a surface with approved 0.25 friction coefficient can be seen here:

Read slides and paper from WSP Parsons Brinckerhoff contribution to the International Heavy Vehicle Transport Technology Symposia HVTT14 15 - 18 November 2016 in Rotorua, New Zealand:

 

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