Predictions of the safety benefits that may be achieved by the introduction of intelligent transport systems are reviewed. It is suggested that these benefits may not materialise if telematics applications (such as route guidance) are poorly designed and distract drivers from the road. Empirical confirmation of the effects of telematics applications is considered necessary and speed limiters (Intelligent Speed Adaptation, ISA) were investigated. Mandatory and advisory speed limiters were considered, using fixed speed limit categories for each stretch of road, variable speed limits allowing for poor road geometry, and dynamic speed limits taking into account the road surface, weather and visibility. Estimates of the reduction in the number of accidents resulting from the use of these speed limit types were made for Great Britain. Mandatory use of the most versatile speed limiter could reduce injury accidents by 35% and fatal accidents by 58%. However this research did not allow for the behaviour of drivers using vehicles fitted with speed limiters, so further tests were carried out using a driving simulator with a realistic vehicle interior. It was hypothesised that drivers in an urban setting would drive more aggressively with the speed limiter fitted. Thirty drivers took part in the experiment. Speed limiting reduced the number of traffic signal violations, reduced close following, resulted in smaller gap acceptance, less physical demand in driving but higher driver frustration. In a further trial with a full range of road conditions, driver with speed limiters were more prone to close following, and with the mandatory speed limiter, relied on the speed limiter to choose an appropriate speed to drive in fog (driving faster than the control group).
Abstract