RELATIONSHIP BETWEEN ILLUMINATION AND FREEWAY ACCIDENTS

The objective of this research was to determine the optimum design illumination level and uniformity needed on urban freeways, as related to accident rates. Data were collected from a wide variety of freeways, and compared by using the ratio of night/ day accident rates per million vehicle miles. The principal findings indicate that an average reduction of 40% in night accidents can be predicted as a result of lighting. Calculated cost-benefit ratios, amortized over 20 yr, are 2. 3, 1. 4, and 1. 7 for freeways with 4, 6, and 8 to 10 lanes respectively. Freeways with measured in-service illumination levels between 0. 3 and 0. 6 horizontal ft-c have the best accident rates.