Daytime running lights in the USA: what is the impact on vehicle crashes in Minnesota?

BACKGROUND Daytime running lights (DRLs) are a safety feature intended to reduce crashes by increasing the contrast between vehicles and the background. AIMS The purpose of this study was to determine whether there is an association between vehicles in the USA being equipped with DRLs and crash rates. METHODS This was a retrospective study using the Minnesota Department of Transportation (MNDOT) Crash Database from 1995 to 2002. Crash reports included in the analyses were limited to accidents involving vehicles 1995 or newer (DRLs not available on prior models) and limited to ideal conditions: (1) daylight, (2) optimal visibility, and (3) dry road surface. The vehicle identification number (VIN) was used to determine the make, model, and year. This information was cross-referenced with a National Highway Traffic Safety Administration table of manufacturer listed DRL conditions to determine vehicle DRL status. Crude crash rates for vehicles were calculated relative to the number of all registered vehicles in Minnesota in 2004, for models 1995-2002. Ninety-five percent confidence intervals (CI) for the rates were constructed assuming a Poisson error distribution. RESULTS During 1995-2002, there were 184,637 vehicles (1995 or newer) with identifiable VINs involved in accidents which occurred under the specified test conditions. Of these vehicles, 37,909 were determined to have standard DRLs and 146,728 were determined to be models without DRLs (including those listed as DRL optional). The crash rate among vehicles without standard DRLs was 1.73 (95% CI: 1.71-1.75) times higher than the rate for vehicles with standard DRLs. The rate ratio was also significant for fatal vehicle crash rates 1.48 (95% CI: 1.23-1.76). CONCLUSION Minnesota vehicles equipped with DRLs were associated with a statistically significant lower crash rate compared to vehicles without DRLs from 1995 to 2002.