Daytime running lights: Its safety evidence revisited.

Retrospective in-depth accident studies from several countries confirm that human perception errors are the main causal factor in road accidents. The share of accident types which are relevant for the effect of daytime running lights (DRL), such as overtaking and crossing accidents, in the total of daylight multiple accidents is larger than in darkness conditions. Perception research leads to the hypothesis that peripheral vision, detection and reaction time are enhanced by DRL, especially under cloudy weather and twilight conditions. Research also show that speeds of oncoming traffic with DRL are overestimated and their distances underestimated compared to non-DRL users. There are also some indications that DRL-use does not mask the perception or reduce the detection time of non-DRL users. These results point to an explanation of a DRL-effect as not only based on increased mere visibility but also based on the enhancement of timely perceptual selection of DRL-users and safer judgements, without an interactive effect on the perception of non-DRL users. The previous evidence for increased safety by DRL comes from national evaluations of a DRL-obligation (Finland and Sweden) and fleet studies (USA and Canada). In the mid eighties less well known evidence came also from Norway (national study on voluntary DRL-use). In an earlier review we concluded that none of these single studies was convincing on its own because of methodological and statistical reasons, but we also argued that the DRL-effect of all studies together is convincing and can be combined to a statistical significant positive linear relation between the magnitude of the DRL-effect and the latitude of the study area. The hypotheses and conditions under which national and fleet studies can be combined are now reconsidered, which lead to a curvilinear relation between DRL-effect and latitude. Evidence from eight recent DRL-studies can be added now: five fleet studies Israel (1), Austria (3), Canada (1)) and three national evaluations (one for the full DRL-obligation in Denmark. One for the later DRL-obligations for Norway and another for a wintertime DRL-campaign in Israel). Although some recent results are less positive, the mean of the recent results per country are quite well predicted by a curvilinear relation between latitude and DRL-effect obtained from the revised analysis of the older results per country. All known studies are now included in a revised analysis for an updated curvilinear relation between latitude and mean DRL-effect per country. The expected overall effect for road safety from DRL for any particular country can be deduced from that curvilinear relation. While other critical questions about the validity of the prognostic prediction of a DRL-effect and with respect to different types of accidents are discussed. (A)