Behavioural adaption and roadway ITS: the forgotten chapter

Although quite some attention is paid to behavioural adaptation issues for driver support systems, BA to roadway ITS is less well documented. Roadway ITS is introduced for its beneficial effects on throughput, safety and emissions. However, negative effects are often neglected. This paper illustrates revealed and theoretical examples of ITS effects that were not designed for. For example: Even though dynamic speed limits are designed to provide throughput benefits during periods of high flow, the presence of the signs and speed enforcement cameras reduce the average speeds also beyond peak hours, increasing general travel times, so even if speed limits are not displayed. Also, dynamic adaptation of speed limits has unexpectedly shown to decrease capacity on some sections and to increase the percentage of rat running traffic to avoid the road section. A more dramatic illustration of BA is shown in case of weather warnings. An automatic fog detection warning system even had an adverse impact in the case of heavy fog with extremely low visibility distances. The activated system resulted in an increase in speed compared to the situation without the fog warning system. Different applications and BA effects are discussed.