Weather presents considerable challenges to the highway system, both in terms of safety and operations. From a safety standpoint, weather (i.e. precipitation in the form of rain, snow or ice) reduces pavement friction, thus increasing the potential for crashes when vehicles are travelling too fast for the conditions. Under these circumstances, the posted speed limit at a location may no longer be safe and appropriate. From an operations standpoint, inclement weather could have considerable impacts on the capacity of the highway system and the efficiency of using the system by motorists. Consequently, new approaches are necessary to influence motorists’ behaviour in regards to speed selection when inclement weather presents the potential for reduced pavement friction at a given location. Among these approaches is the use of Variable Speed Limit (VSL) systems. This document presents the results of initial work completed in the development of such a system. The work completed included a literature review related to different aspects and types of VSL systems, as well as a review of sensor systems capable of providing roadway grip/friction measurements. The work also developed a Concept of Operations and Requirements for the prospective VSL system, with detailed information provided in the Appendix. Sensor testing was completed on the Vaisala DSC 111 to determine its accuracy and applicability for inclusion in the prospective VSL. Finally, a policy and legal implications review that was completed by Oregon Department of Transportation staff including a summary of Oregon’s recently enacted administrative rules on use of variable speed limits and statutes and rules adopted by other states is presented. (Author/publisher)
Abstract