Improving speed behaviour: the potential of in-car speed assistance and speed limit credibility

Speeding is still a common practice on many roads and it contributes to a significant number of crashes. Two new approaches to solve speeding issues are focused on: intelligent speed assistance systems (ISA) and speed limit credibility. Research has indicated that ISA is promising with respect to improving speed behaviour but has not been widely implemented yet. Another promising approach to reduce speeding involves adjusting the environment to improve the speed limit credibility. The aim here is to investigate the potential of both approaches and particularly the potential of the combination of these measures. A driving simulator study was conducted to investigate the individual and combined effects of the use of an ISA system and the speed limit credibility on drivers´ average speed and the amount of time spent speeding. The results indicated that both the informative ISA system used here and the speed limit credibility significantly improved speed behaviour. Drivers not using ISA appeared to be more susceptible to the speed limit credibility than those using ISA. It is concluded that both the measures can be effective to improve speed behaviour. The results obtained suggest that the properties of this particular informing and warning type of ISA could have resulted in the speed limit credibility neither affecting the amount of time speeding nor the average speed.