Effect of environmental factors on the risk of death for drivers of two-wheeled motorized vehicles involved in road crashes

Objectives: To assess the effect of environmental factors on the risk of death for drivers of two-wheeled motorized vehicles (TWMV) after a crash. Methods: We studied a case series comprising all 309,626 drivers of TWMV involved in road crashes with victims compiled by the Spanish Department of Transportation from 1993 to 2002. The dependent variable was death of the driver. Environmental factors included temporal variables (year, month, day and hour of the crash) and spatial variables (area where the accident took place and light conditions, among others). Confounding variables related to the driver (age, sex, helmet use), the vehicle, and the type of crash were also recorded. Poisson regression models were constructed to obtain crude and adjusted relative risks for each environmental condition. Results: In the adjusted analysis, no association was found between most time-related factors and the risk of death, with the exception of an increased risk in the early hours of the morning. The risk of death was much greater for crashes on open roads (especially highways and motorways) than in urban areas, where the risk of death increased as the size of the town decreased. Conclusions: After adjustment for several confounders, the only environmental factors related to the risk of death in TWMV drivers after a crash were the area when the crash occurred, and (more weakly) the time of day when it occurred. Key words: Traffic accidents. Motorcycles. Death. Risk factors. Environment.