Abstract
Daylight savings time (DST) takes place each year from 2:00 a.m. on the first Sunday in April to 2:00 a.m. on the last Sunday in October. It is expected that the changes to and from DST could positively or negatively affect safety. In fact, previous research has shown that these changes indeed affect safety, but many studies suffered from methodological limitations, including erroneously extrapolating short-term effects to long-term conditions. Given these limitations and contradictory results, there is a need to reexamine the effects of DST on the number of motor vehicle and pedestrian crashes. The primary objective of this study was to quantify the safety effects of DST through the use of statistical modeling for the morning and afternoon 5-h periods at the boundary delimiting dark and light conditions. The secondary objective consisted of conducting a before-and-after study to estimate the immediate effects following the change to and from DST. To quantify the potential safety effects of DST, model outputs were applied to different hypothetical time intervals during the year, including the newly proposed DST extension by the U.S. Congress. The results of the study showed that the statistical models performed as expected, with the exception of one model, with which the number of crashes decreased with an increasing proportion of daylight conditions in the 5-h period. The application of the models to different scenarios showed that the absolute difference in predicted crashes was relatively small between scenarios, a finding that supported previous work on this topic.
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