Daytime running lights (DLRs) reduce the number of daytime accidents. Daytime vehicle lighting ensures a greater contrast between vehicle and environment, which makes approaching vehicles more conspicuous.
In-depth studies of accidents show that in 50% of the daytime accidents, the other road user was not discerned or discerned too late; at intersections, this is even the case in 80% of the accidents . On the basis of theoretical evidence and observational research, the beneficial effect of daytime running lights is, above all, explained by the greater contrast between a vehicle and its environment: this increases the conspicuousness of vehicles and makes them more easily identifiable (recognizable as an approaching motor vehicle). An additional effect is that vehicles with DRLs are estimated to be closer than they really are. This results in approaching traffic taking fewer risks during overtaking manoeuvres and during approaches at intersections .
A worlwide meta-analysis of 41 studies into the effect for cars and 16 studies into the effect for motor cycles shows that DRLs reduce the number of daytime injury crashes by 3-12% . The effect on the number of fatal crashes can be estimated to be a little higher (-15%). DRLs on motor cycles lead to a 5-10% reduction in the number of injury crashes. What should be noted is that the results per study differ greatly . A more recent study showed that DRLs reduced the number of head-on crashes and side impact crashes by 12%; the number of accidents involving cars and pedestrians/cyclists even decreased by 20% (Hoye, 2014 mentioned in ). According to Koornstra et al.  the effect appeared to be dependent on the degree of latitude of a country. Eriksson en Sandin  conclude that present research shows that DRLs have a positive effect on road safety, but there is no consensus about the extent of the effect.