Abstract
This study considered the optimum amount of information that should be presented on an incident warning system. It was assumed that a low level of detail would produce a high variation in driver behaviour due to different interpretation and that a high level of information would reduce variation. A simulation study was carried out to test this. The warning systems used were PORTICO and 3 versions of MELYSSA. All incident warning systems had positive effects on traffic safety. It is suggested that the optimum level of information that should be displayed depends on the incident and the reactions required.