Evaluation of the conspicuity of daytime running lights.

In both Scandinavia and Canada, Daytime Running Lights (DRLs) have been required for use on all motor vehicles to improve their conspicuity and to reduce crashes. To help evaluate the possible benefits of using DRLs in the United States, the National Highway Traffic Safety Administration sponsored research to quantify the relationship between vehicle detectability and DRL intensity over a range of ambient light levels characteristic of the U.S. environment. The results showed that 1,600 candela was the minimum DRL intensity needed to significantly improve vehicle detectability under ambient light levels below 4,000 footcandles of horizontal illuminance. Under brighter conditions, DRL effectiveness was greatly diminished. (A)