Evaluation of a fixed anti-icing spray system

Each year hundreds of automobile drivers have accidents caused by iced-over bridges adjacent to roads that are free from ice. Ice forms on bridges because the ground does not insulate them; therefore, the temperature of a bridge deck rapidly cools to the ambient air temperature, which is often well below freezing. This is particularly evident on the Interstate 215 overpass/exchange at 6200 South Street in Salt Lake City, Utah. This bridge averages more than 24 accidents per winter season because of snow and ice conditions. A system was installed at this location that applied the anti-icing liquid agent magnesium chloride (MgCl₂) to the northbound lanes of the freeway bridge deck. The southbound lanes received no additional treatment, other than the efforts of the Utah Department of Transportation's snow- and ice-removal operators. The anti-icing spray system is parapet-mounted and delivers approximately 360 L/lane-km/spray (95 gal/lane-km/spray) event of MgCl₂. The effectiveness of the spray system was analyzed for the 1997 and 1998 winter season. The system reduced the number of accidents caused by snow and ice on the northbound side of the road by 64 percent. The ratio of the number of accidents occurring on the treated northbound side of the road to the number of accidents occurring on the untreated southbound side was reduced from 1.4 to 0.7. The anti-icing system proved effective in reducing the number of accidents that occur on this very dangerous section of roadway in Utah.