Daytime running lights project. IV: Two-lane passing performance as a function of headlight intensity and ambient illumination.

The experiment investigated the ability of subject drivers to perform a two-lane passing task, with oncoming traffic, as a function of the level of ambient illumination and the headlight intensity of the oncoming vehicle. Results indicated that the gaps accepted by drivers in a two-lane passing situation increased with an increase in the intensity of the headlight of the oncoming vehicle. The range of gaps accepted across headlight conditions was less, however, at higher levels of ambient illumination than at lower levels.