Integrating remote weather stations and road surface condition monitoring into variable message sign (VMS) control strategies offers dramatic improvements in road safety. This article discusses the study of a variable speed limit VMS system on a 14km experimental section of the E18 highway in southern Finland. About 12km of the section is new motorway, and 2km is old road. There are 36 variable speed limit signs, and five message boards to warn about hazardous conditions or other factors affecting traffic. Local weather and road surface conditions are monitored automatically from two unmanned stations on the section. Station data are transmitted by cable every five minutes to a central computer, which calculates appropriate speed limits. The section can be divided into four separately controlled zones, each displaying a speed limit of 80, 100, or 120kph according to road conditions, rain, visibility, and wind. 120kph is set for good conditions, 80kph when there is snow or ice on the road, and 100kph otherwise. When wind speed exceeds 12 and 17m/s, speed limits are set to 100 and 80kph, respectively. A three-year study is being conducted in conjunction with the experiment, to identify the effects of variable speed limits in terms of driver behaviour, traffic safety, and road maintenance.
Abstract