Purpose: We investigated certain possible adverse effects of daytime running lights (DRL) , originating from perceptual or cognitive mechanisms. In particular, OUT study dealt with the possibility that road users in the vicinity of a DRI-vehicle would suffer from a decreased conspicuity because of the presence of that vehicle. Methods: We conducted two experiments. The main experiment investigated the primary effects of DRL on/off on the conspicuity of other road users in the vicinity, with particular attention to other factors that might moderate the magnitude of any DRL-effect (type of background, type of other road user, level of expectation with regard to DRL, etc.) The additional experiment studied the effects of DRL on/off as a function of drivers' visual and attentional capacities, notably Useful Field of View (UFOV) and static visual acuity. This experiment, therefore, checked for the possibility that DRL effects might be moderated by certain characteristics of the driver population. In both experiments, subjects viewed colour slides depicting natural daylight scenes of traffic intersections. The slides were taken under overcast skies, representing the condition in which DRL should have its maximum effect. The slides contained a car with or without DRL and possibly other road users such as a cyclist, pedestrian or motorcyclist. Subjects were instructed to determine whether any other road users were present or not (present-absent search task) , and they were instructed to react as fast as possible. Their reaction times were the main dependent variable. Results: The effect of DRL in the main experiment showed that when the car had its headlights on, the subjects reacted faster than when the headlights were off. In other words, the other road users were on average detected better when the car had its headlights on. This effect is contrary to the hypothesis that other road users will suffer from the presence of a DRL-vehicle. However, considering the difference of 13 milliseconds on a grand average reaction time of 929 milliseconds it is not really a large effect in the opposite direction either. When looking in depth for negative effects that might, nevertheless, occur in specific stimulus situations we found no such effects. It was therefore not the case that the grand average effect of DRL hid an opposite effect that could have occurred somewhere in a specific combination of conditions. In the additional experiment we found no interaction effects between DRL on the one hand and UFOV and visual acuity on the other. This finding suggests that UFOV and visual acuity do not moderate the effects of DRL. Conclusions: Overall, we conclude that we found no evidence that the conspicuity of road users in the vicinity of a DRL-vehicle, as measured by the speed with which their presence was detected, suffered from a car having its Daytime Running Lights on. Also, there was no evidence that road users with certain visual capacities that are less than average would specifically suffer from contraproductive effects of DRL. (Author/publisher)
Samenvatting