Intelligent Speed Adaptation: Evaluating the possible effects of an innovative speed management system on driver behaviour and road safety

The research reported in this thesis provides a comprehensive safety evaluation of Intelligent Speed Adaptation (ISA) using a range of experimental methodologies. An ISA system can have varying system characteristics but, in general, limits a vehicle to a particular speed (or provides advice about the appropriate speed). This evaluation offers an important contribution to the understanding of a range of issues pertinent to the implementation of such a technology. This thesis reports a series of studies designed to evaluate the effect of ISA on driver behaviour and safety. Each of the studies addressed a separate issue and thus a number of research methodologies were used. The studies evaluated the effectiveness of ISA in comparison to other speed-reducing methods and investigated how drivers interacted with ISA across a variety of road types. In addition, a number of variants of ISA were developed and their comparative effectiveness was studied in a laboratory setting and in the real world. In summary, the simulator studies reported decreases in mean and maximum speeds for areas of interest such as curves and village entry points. The field studies on the other hand only found decreases in maximum speeds, probably due to the small sample and high variability in traffic conditions. However these decreases in speed were located in road environments where excessive speed is a problem; thus safety benefits would undoubtedly accrue with ISA. With regards to system design, drivers were more accepting of an ISA system that allowed an override particularly self-reported speeders. Increases in frustration and the perceived loss of time while driving with a mandatory ISA were also reported and may explain the negative shift in gap acceptance behaviour and car following observed in the simulator.