The influence of daylight saving time on motor vehicle fatal traffic accidents

Abstract

This paper shows that Daylight Saving Time (DST) reduces fatal traffic accidents involving motor vehicles by approximately one percent, during several weeks at the spring and fall DST transitions. There is also a net reduction of about 0.7% during the DST period, March and April 1974, compared to the non-DST period, March and April 1973. However, there is little net DST effect on fatal accidents in the winter. The basic method employed to obtain this estimate of the effect of DST on motor vehicle accidents is to compare numbers of persons killed (fatalities) in these accidents during both DST and non-DST periods. This is accomplished by identifying high frequencies in the Fourier spectrum of traffic fatalities which are relatively sensitive to DST, and then using a bandpass filter to remove low frequency components not associated with DST. A cause/effect relationship between DST and fatal traffic accidents is then established by measuring changes in the filtered time series of fatality data across DST transitions, and across non-DST or control transitions. Certain statistical criteria are then applied to these measurements in order to confirm the existence of a DST effect on fatal traffic accidents and resulting fatalities.