Intelligent speed adaption ISA : a new perspective

This contribution will give a brief overview of past and current European research activities in the area of Intelligent Speed Adaptation (ISA). Next, a series of studies is described in which functionalities of ISA and Adaptive Cruise Control (ACC) were combined. The first study consisted of a driving simulator experiment with an ACC; external speed information was available in either an informative mode or in an intervening mode. The results revealed that ACC yields more consistent longitudinal control: in car-following situations, there is less variation in headway and in speed. Only intervening systems result in a speed reduction on motorway sections with a special speed limit, but at a cost of somewhat higher speeds at non-controlled sections. In critical scenarios (approaching a sudden traffic queue) where ACC could not cope with completely and the driver had to take over control, a somewhat later braking reaction of the driver was found. In another study, the effect of this system on traffic flow on motorways was examined by means of microscopic traffic simulation. Results showed that as the penetration level of this system increases, the mean speed, standard deviation of speed, and percentage of critical TTCs decreased. In conclusion, automatic speed limiting by an in-car device seems most promising, although concern about behavioural adaptation mechanisms may apply.