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Report numberRA-2005-73
TitleLowering the speed limit for trucks
SubtitleEffects on traffic safety
AuthorsKurt Van Hout
Erik Nuyts
An Dreesen
Published byPolicy Research Centre for Traffic Safety 2002-2006
Number of pages82
Date06/12/2005
ISBN
Document languageDutch
Partner(s)PHL
Work packageOther: Behaviour
Summary

The Flemish government considers the installation of a lower speed limit for trucks. Heavy trucks (heavier than 7,5 t) are now limited to 90 km/h on freeways, lighter trucks (between 3,5 and 7,5 t) are limited to 120 km/h. In the future this speed limit should be reduced to 80 km/h for all of them. This report intends to assess the effects of this measure on traffic safety.

 

Based on the literature review we looked into the impact a lower speed limit for trucks has towards real speeds and the speed variation among the different vehicles. From the literature we know that lowering speed limits results most of the times in a lower speed. Because the lower speed limit is only adopted to a certain group of vehicles, dispersion in the overall traffic stream increases.

 

Next the correlation between speed and crash rate is considered. International literature shows that a lower speed is associated with a lower crash rate. The impact of speed variation is less clear. Vehicles that drive faster than the mean speed have a higher risk of collisions. For vehicles that travel slower than the mean speed this clear connection does not exist. Some studies state that they also are subject to a higher crash rate, while other studies don’t find this higher crash rate. Not only is the crash rate influenced by speed. Speed also affects the severity of a crash. The higher the speed, the higher the severity of the crash. All researchers agree on this topic.

 

The effect of a lower speed limit can be augmented by means of supportive measures. Europe obliges the use of a speed limiter for all trucks heavier than 3,5 t. Belgium obliges for now the use of a speed limiter only for trucks above 12 t. The speed is limited to 90 km/h (and not 80 km/h). An other measure considered is an overtaking ban for trucks on freeways.

 

Based on the relations found in the literature an estimate is made of the gains in traffic safety on Flemish freeways. The reductions of the number of injury accidents, injuries and vehicles involved are calculated following some possible scenarios. All calculations show a reduction in the number of accidents on Flemish freeways of 1 to 6%. But the calculations also show that if the difference in speed between trucks and passenger cars becomes too large, the gain in traffic safety becomes less pronounced. From the scenarios used, the combination of a decrease in speed limit for trucks to 80 km/u together with a speed limiter seems the best option.

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Mission

The Policy Research Centre for Traffic Safety carries out policy relevant scientific research under the authority of the Flemish Government. The Centre is the result of a

cooperation between Hasselt University, KU Leuven and VITO, the Flemish Institute for Technological Research.

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