Weather threatens surface transportation nationwide and impacts roadway safety, mobility, and productivity. Weather affects roadway safety through increased crash risk, as well as exposure to weather-related hazards. Weather impacts roadway mobility by increasing travel time delay, reducing traffic volumes and speeds, increasing speed variance (i.e., a measure of speed uniformity), and decreasing roadway capacity (i.e., maximum rate at which vehicles can travel). Weather events influence productivity by disrupting access to road networks, and increasing road operating and maintenance costs. There is a perception that transportation managers can do little about weather. However, three types of road weather management strategies may be employed in response to environmental threats: advisory, control, and treatment Strategies. Advisory strategies provide information on prevailing and predicted conditions to both transportation managers and motorists. Control strategies alter the state of roadway devices to permit or restrict traffic flow and regulate roadway capacity. Treatment strategies supply resources to roadways to minimize or eliminate weather impacts. Many treatment strategies involve coordination of traffic, maintenance, and emergency management agencies. These mitigation strategies are employed in response to various weather threats including fog, high winds, snow, rain, ice, flooding, tornadoes, hurricanes, and avalanches. This report contains 30 case studies of systems in 21 states that improve roadway operations under inclement weather conditions. Each case study has six sections including a general description of the system, system components, operational procedures, resulting transportation outcomes, implementation issues, as well as contact information and references. Appendix A presents an overview of environmental sensor technologies. Appendix B is an acronym list. Appendix C contains online resources, including 39 statewide road condition web sites. In Appendix D hundreds of road weather publication titles, abstracts and sources are tabulated.
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