The relation between the end date of daylight saving time and the number of road traffic casualties : is there an increase in the number of casualties when the clock is set back one hour? In the General Discussion on Road Safety that took place on 30 January 2013, Member of Parliament De Graaf asked Minister Schultz van Haegen for Infrastructure and the Environment what is known about the road safety effects of the clock being set back one hour at the end date of daylight saving time (DST). He referred to a study by the Belgian Institute for Road Safety BIVV, which he believed to indicate that the clock being set back at the end date of DST is the cause of considerable traffic misery. In reaction to this question, SWOV investigated what is known about this subject, and to which extent passing the end date of DST results in a change in the number of serious crashes in the Netherlands. SWOV carried out the study by graphic analysis of data (crashes, casualties, and mobility) for all times of day and all days of the year during a period of several decades. The study indicates that setting back the clock at the end of DST (which since1996 is done on the last Sunday in October) has indeed coincided with an increase in the numbers of road crashes and casualties during a specific part of the day. However, these higher numbers were also found in consecutive months, which suggests that setting back the clock in itself does not necessarily have an effect on road safety. It seems more likely that the effect can be explained from the fact that in winter a greater proportion of the evening rush mobility takes place during twilight and in the dark. This is due to the fact that dark commences earlier when DST comes to an end and thus causes a greater proportion of the evening rush to take place in the dark. This probably results in a higher number of road casualties, because the risk (number of injury casualties per distance travelled) appears to be higher during dusk and dark than during daylight. This is especially the case for pedestrians. Finding the cause for the increase in crashes and casualties during dusk and dark in the winter months is an interesting subject for a follow-up study. The results of the present study do not support the assumption that the clock being set back an hour at the end of DST has an effect on road safety. It must also be noted that in winter ‘the original time’ is restored as an adjusted time is used in summer. It is therefore likely that casualties are saved during the summer due to the shift to DST which results in a greater proportion of mobility during daylight hours. This aspect is also mentioned in other research reports. From the road safety point of view it is worthwhile investigating how many casualties can be saved by making DST the standard time.
Samenvatting