Effects of weather-controlled variable message signing on driver behaviour: Dissertation

This study investigated the effects of local and frequently updated information about adverse weather and road conditions on driver behaviour. The information was transmitted by several types of variable message signs (VMS). Two evaluations investigated the effects of VMS systems involving an individual sign or two signs; two other evaluations focused on more extensive VMS systems involving several signs, and two evaluations studied the effects of the sign technology. The slippery road condition sign and minimum headway sign decreased the mean speed of cars travelling in free-flow traffic by 1-2 km/h. The minimum headway sign also decreased the proportion of short headways. In addition, drivers' reports suggested that these variable message signs have other effects on driver behaviour, such as the refocusing of attention to seek cues on potential hazards, testing the slipperiness of the road, and more careful passing behaviour. Lowering the speed limit from 100 km/h to 80 km/h on a weather-controlled road decreased the mean speed by an average of 3.4 km/h in winter. The system proved most effective when adverse weather and road conditions were not easy to detect. The system also decreased the standard deviation of speed. Most drivers accepted lowered speed limits and found variable speed limits useful. Variable speed limit signs using fibre-optic technology were found to be more effective than electromechanical signs. However, effective signs may divert the driver's attention from adjacent fixed signing. The slippery road condition sign is recommended for careful use at critical spots, whereas a system including variable speed limits is recommended for somewhat longer road sections. The use of fibre-optic signs is recommended for weather-controlled applications.