Evaluation of A16 Motorway Fog-Signaling System with Respect to Driving Behavior

On the A16 Motorway in the Netherlands, the Dutch Ministry of Transport implemented an automatic fog-signaling system to elicit safer driving behavior during fog. Along a road section 12 km (7.4 mi) long, 20 sensors were placed to continuously measure the visibility range. During fog, the system displays an explicit fog warning on overhead matrix signs together with a maximum speed limit that depends on the actual available visibility range. An evaluation study in terms of driving behavior was carried out for a period of more than 2 years. Continuous traffic measurements for individual vehicles were obtained via inductive loop detectors at six locations (four experimental and two control locations). Data on the local visibility conditions and on the messages displayed on the matrix signs were available on a 1-min basis. The results reveal that the system has a positive effect on speed choice in fog: on top of a lower mean speed caused by the reduced visibility, the system results in an additional decrease of speed of about 8 to 10 kph