<P> In 1975 the U.S. DOT conservatively identified a 0.7% reduction in traffic fatalities during DST, and estimated the real reduction at 1.5% to 2%, but the 1976 NBS review of the DOT study found no differences in traffic fatalities . In 1995 the Insurance Institute for Highway Safety estimated a reduction of 1.2%, including a 5% reduction in crashes fatal to pedestrians . Others have found similar reductions . Single / Double Summer Time (SDST), a variant where clocks are one hour ahead of the sun in winter and two in summer, has been projected to reduce traffic fatalities by 3% to 4% in the UK, compared to ordinary DST . However, accidents do increase by as much as 11% during the two weeks that follow the end of British Summer Time . It is not clear whether sleep disruption contributes to fatal accidents immediately after the spring clock shifts . A correlation between clock shifts and traffic accidents has been observed in North America and the UK but not in Finland or Sweden . If this effect exists, it is far smaller than the overall reduction in traffic fatalities . A 2009 U.S. study found that on Mondays after the switch to DST, workers sleep an average of 40 minutes less, and are injured at work more often and more severely . </P> <P> In the 1970s the U.S. Law Enforcement Assistance Administration (LEAA) found a reduction of 10% to 13% in Washington, D.C.'s violent crime rate during DST . However, the LEAA did not filter out other factors, and it examined only two cities and found crime reductions only in one and only in some crime categories; the DOT decided it was "impossible to conclude with any confidence that comparable benefits would be found nationwide". Outdoor lighting has a marginal and sometimes even contradictory influence on crime and fear of crime . </P> <P> In several countries, fire safety officials encourage citizens to use the two annual clock shifts as reminders to replace batteries in smoke and carbon monoxide detectors, particularly in autumn, just before the heating and candle season causes an increase in home fires . Similar twice - yearly tasks include reviewing and practicing fire escape and family disaster plans, inspecting vehicle lights, checking storage areas for hazardous materials, reprogramming thermostats, and seasonal vaccinations . Locations without DST can instead use the first days of spring and autumn as reminders . </P> <P> A 2017 study in the American Economic Journal: Applied Economics estimated that "the transition into DST caused over 30 deaths at a social cost of $275 million annually," primarily by increasing sleep deprivation . </P>

What's the real reason for daylight savings time