Best Practices for Road Weather Management Version 2.0
Effect of Environmental Factors on Free-Flow Speed
The draft chapter on freeway facilities, to be included as chapter 22 of the Highway Capacity Manual 2000, notes that "adverse weather can affect not only capacity, but also reduces operating speeds significantly." The chapter cites several studies that investigated the effects of rain, snow, and fog on both capacity and speed. The authors have studied the effects of a variety of weather-related environmental factors on driver speeds as part of an Intelligent Transportation Systems project that has been ongoing in Idaho since 1993. Visibility and roadway sensors were installed on a segment of I-84 in southeastern Idaho in 1995. This project has generated substantial data on traffic flow rates and driver speeds during periods of reduced visibility and other hazardous driving conditions. While capacity is not an issue along this section of rural interstate freeway, the sensor infrastructure now in place provides an opportunity to determine the effects of various factors on free-flow speed. This study reports on data collected during two winter periods, 1997-1998 and 1998-1999.
Fourth International Symposium on Highway Capacity
Kyte, Khatib, Shannon, Kitchener
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