Tackling Methodological Issues in Studying Bicycling Safety: Illustration Using Bicyclists’ Injuries and Cycling Environment Study

Bicycling is a less attractive transportation mode than driving in much of the world because it is often less safe. Differences in injury rates between jurisdictions with different cycling infrastructure indicate that studying route design should be a fruitful avenue of investigation to improve safety and increase ridership. However, such research has been limited by problems associated with measuring exposure to route infrastructure (the denominator necessary for risk calculations) and accounting for potential confounders (e.g., risk-taking behaviour, weather conditions). This paper discusses these methodological issues and how researchers can address them using the case-crossover design. We illustrate the design by describing the Bicyclists' Injuries and the Cycling Environment Study, and present data on its feasibility. Injured cyclists were recruited from the emergency departments of five hospitals in Vancouver and Toronto, Canada. In 18 months, 690 participants were successfully recruited and interviewed. Each participant was interviewed to map the route of their injury trip, identify the injury site, and to select two control sites at random from the same route, thus adjusting for exposure to risk. The case-crossover analysis will compare infrastructure at the injury site to control sites within the same trip, thus preventing confounding. A concern about within-trip comparisons is insufficient variance in the transportation infrastructure, but preliminary data demonstrate that almost all trips included multiple infrastructure types. Future studies could replicate this design in other locations to expand the range of cycling infrastructure compared and facilitate evidence-based cycling infrastructure design to make cycling safer and more appealing.