The present study is a part of the Danish ISA project “Pay as You Speed” (http://www.sparpaafarten.dk ). The project is still running and the results reported here stem from a first data collection by April 2007. The general idea of ISA is well known from several previous studies (see Warner, 2006 for a review). With respect to traffic safety informative ISA is a most promising device, provided that drivers do use the system as a support for adhering to the speed limit during driving. If they do not, ISA is just another source of distraction. In most ISA projects driver motivation has not been an issue; the recruitment of volunteers have proceeded successfully and a substantial effect of informative ISA has been observed in all ISA studies, though it has been reported, that the effect of informative ISA tends to decrease after long term use (Warner, 2006). This finding suggests that maintenance of the initial positive effect of informative ISA requires maintenance of driver motivation as well. As researchers of behaviour in traffic, we may, and should, question the reliability of ISA effects measured in previous studies for (at least) two reasons, (1) the general use of volunteers may bias the result, and (2) the almost complete ignorance of driver motivation. (Author/publisher)
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