Background: It has been suggested that the transition phases of implementing daylight saving time (DST) may impact on serious or fatal injuries sustained as the result of road traffic collision (RTC). The aim of this study is to explore the effects of transitions into and out of daylight saving time on the incidence of such injuries.

Methods: This is a comparative observational study of 11-year of data submitted prospectively to the Trauma Audit Research Network (TARN) between 1996 and 2006. Data for 4 weeks before and after time transition in spring and autumn of each year was collected. The time periods selected reflect those hours with maximum light level changes due to time alterations (2-hour around sunrise and 4-hour around sunset). Travellers outside those hours are unlikely to be affected by the changes.

Results: Out of 55,826 incidents in England and Wales, TARN returned 1296 incidents meeting the above time criteria, of which 282 involved a fatality. Overall, there were more crashes in autumn (845, 65.2%) comparing to spring period (451, 34.8%), with the majority occurring around sunset (1057, 81.5%). RTC related injuries at the onset of DST in spring showed a significant increase up to 14 days post time change (P=0.029), with the majority of the increase occurring at sunset. The highest increases occurred within the fatal incidents group (P=0.0019) and affected mainly the pedestrian subgroup (P=0.013). Changes in the incidence of injuries around the change back to Greenwich Mean Time (GMT) in autumn did not reach significance.

Conclusion: The use of DST over the period studied was associated with rise in RTC related injury figures up to two weeks following the spring time transition. These findings inform the continuing clock changes debate. The introduction of 2-hour time change may result in detrimental effects on RTC related injuries.