Development of an Algorithm for Using Dynamic Speed Limits in Relation to the Weather Situation

This paper describes an ongoing research project in the Netherlands that lowers the speed limit on highways based on the weather condition (in particular, rain) to enhance traffic safety. The authors describe three phases of the project: the strategy of speed limits to be displayed, i.e., in what situations the speed limit should be lowered and how these limits will be shown to the drivers; the usefulness and accuracy of a weather radar system for the prediction of showers on a motorway; and the development of an algorithm that determines the appropriate speed limits. The variable message signs (VMS) that are already used to warn drivers of congestion ahead or lane closures will be used to incorporate the variable speed. The authors also briefly review the literature regarding the problematic impact of adverse weather conditions on road safety. The rain algorithm will be implemented in the Dutch system for showing speeds on matrix panels on overhead gantries above the road in the fall of 2008. Already, the researchers are collecting data with rain gauges along the test highway A12 between Rotterdam and Utrecht (The Netherlands).