VISIBILITY IN BLOWING SNOW AND APPLICATIONS IN TRAFFIC OPERATIONS

Wind and visibility data continuously transmitted from two monitoring stations on I-80 between Laramie and Rawlins, Wyoming, are analyzed real-time by a computer. Summaries of conditions are printed out hourly, with recommended regulations and warnings when minimum standards are exceeded. Required speed limits are determined by equating stopping sight distance to the hourly average minimum visibility, and solving for vehicle speed. Studies reported here show that for wind speeds greater than 7 m/s in blowing snow, visual range (V) is related to wind speed (U) according to V - AU to the power minus 5, where the A coefficient changes in response to snow availability. The coefficient calculated from the incoming data is used to index snow conditions, predict visibilities based on wind forecasts, and detect snowfall. This information is used for road closure or opening decisions, and to estimate time required for visibility to reach the precribed standard for opening a road. Computerized analysis of weather data is essential for timely and objective traffic operations decisions, and the relationship between wind and visibility in blowing snow can provide the basis for standards that are technically sound and unambiguous. /Author/