Exposure measurement in bicycle safety analysis: A review of the literature.

BACKGROUND Cycling, as an active mode of transportation, has well-established health benefits. However, the safety of cyclists in traffic remains a major concern. In-depth studies of potential risk factors and safety outcomes are needed to ensure the most appropriate actions are taken to improve safety. However, the lack of reliable exposure data hinders meaningful analysis and interpretation. In this paper, we review the bicycle safety literature reporting different methods for measuring cycling exposure and discuss their findings. METHODS A literature search identified studies on bicycle safety that included a description of how cycling exposure was measured, and what exposure units were used (e.g. distance, time, trips). Results were analyzed based on whether retrospective or prospective measurement of exposure was used, and whether safety outcomes controlled for exposure. RESULTS We analyzed 20 papers. Retrospective studies were dominated by major bicycle accidents, whereas the prospective studies included minor and major bicycle accidents. Retrospective studies indicated higher incidence rates (IR) of accidents for men compared to women, and an increased risk of injury for cyclists aged 50 years or older. There was a lack of data for cyclists younger than 18 years. The risk of cycling accidents increased when riding in the dark. Wearing visible clothing or a helmet, or having more cycling experience did not reduce the risk of being involved in an accident. Better cyclist-driver awareness and more interaction between car driver and cyclists, and well maintained bicycle-specific infrastructure should improve bicycle safety. CONCLUSION The need to include exposure in bicycle safety research is increasingly recognized, but good exposure data are often lacking, which makes results hard to interpret and compare. Studies including exposure often use a retrospective research design, without including data on minor bicycle accidents, making it difficult to compare safety levels between age categories or against different types of infrastructure. Future research should focus more on children and adolescents, as this age group is a vulnerable population and is underrepresented in the existing literature.