Speed impacts of an icy curve warning system

Abstract

Icy pavements can impair the ability of drivers to operate their vehicles safely. The California Department of Transportation has deployed an icy curve warning system (ICWS) on a five-mile segment of SR 36 in Lassen County. This section of roadway has a history as a high-crash location with fatal crashes, the vast majority of which occurred during icy pavement. The objective of this study was to evaluate operational effects of the ICWS, specifically on speeds during various conditions. The results of statistical analysis found that mean speeds were significantly different by greater than 5 mph when the system was on against off in general, as well as when examined by day and night. Mean speeds were significantly reduced by greater than 5 mph during wet weather (during day and night). The real interest of the evaluation was the system's impacts on reducing speeds during conditions when ice was present but unexpected (called clear, cold and not dry in this work). Statistical analysis found that mean speed reductions were significant by greater than 3 mph (but less than 5 mph) when the system was on both during the day and at night. Consequently, the ICWS appears to reduce speeds by approximately 3 mph in conditions where icy roads are unexpected.