1 ESTIMATING ADVISORY ISA SYSTEM SAFETY IMPACT AT VARYING IMPLEMENTATION LEVELS

This paper discusses a number of hypotheses concerning the safety effects brought about by the use of an advisory Intelligent Speed Adaptation (ISA) system at varying levels of implementation. To date much of the research related to ISA has been concerned with the investigation of existing mandatory intervening systems and the extent to which these succeed in reducing speed and speed variance. Little attention has been paid to speed warning devices. These systems are not likely to have the same safety enhancing effects, but are more likely to receive acceptance from vehicle drivers. In order to estimate the effects of the advisory ISA system, it is also useful to know something of the unwanted behavioural adaptation effects that reduce the net safety gain. A joint project has been started with the intention of investigating and estimating the safety impact of a speed-warning device that is currently being used in a large-scale trial. The methodology of this project involves the collection of data using field studies, data logging of the ISA-equipped vehicles, instrumented vehicles, and interviews and questionnaires related to drivers behaviour and attitudes. In order to estimate the safety (and efficiency) effects at different implementation levels, micro-simulation is used. This simulation is based on a detailed model of driving behaviour that is sensitive to the changes brought about by a speed-warning system. At the present time, the data is undergoing analysis hence the hypothetical nature of the effects that are discussed and focus on background and methodological issues