This report describes a driving simulator experiment carried out to study the effect of Variable Message Sign (VMS) distance in an Automatic Incident Detection (AID) system on driving behaviour. In a simulated motorway environment, participants were now and then confronted with a stationary traffic queue. Subjects completed several runs with and without AID. The VMS distance (300, 700, 1500 m) and the traffic condition were varied. In runs with AID, subjects first passed a VMS showing `70' (km/h) followed by a VMS showing `50' (km/h) before reaching the queue tail. The results show that the AID system results in the intended changes in driving behaviour when approaching stationary traffic queues. With AID, the speed reduction process starts at a larger distance concerning the queue tail, and the occurring maximum decelerations are smaller. The AID results in an increase of the minimum Time-to-Collision (TTC) in the phase up to the final approach part of the manoeuvre. When comparing the queue approach processes in the separate VMS distance conditions, the behaviour found with 1500 m VMS distance is somewhat less favourable than with 700 or 300 m. When the AID only activates 2 signs upstream of the queue tail, the 700 m VMS distance is preferable over the 300 m VMS distance. Therefore, more than two signs upstream of the incident should be activated in order to fully benefit from an AID with small (300 m) VMS spacing.
Samenvatting