Abstract
During the last years opponents against mandatory use of Daytime Running Lights (DRL) have used the accident statistics, presented in two VTI reports, in which effects of DRL on accidents have been analysed and evaluated. These opponents argued that these statistics do not show any effects at all or that the effects are artefacts and thus depending on irrelevant factors. It is, however, quite evident that causal relationship between change of traffic safety over time and the introduction of the mandatory DRL has not been established in these reports.