Improving the Denominator of Safety Rankings for Bicyclist and Pedestrian Safety.

Active transportation increases physical activity and improves health, yet rising pedestrian and bicyclist deaths are a growing public health concern. In North America, regional agencies allocate transportation investments to support safe walking and bicycling. While comparing crash statistic across regions is standard, accurate safety assessment requires exposure data, or the volume of active transportation users, to determine crash rates. Calculating spatial variation in crash rates is difficult given the lack of spatially detailed, regionally extensive exposure data. Our goal is to develop a method to compare bicycling and pedestrian safety between cities, to inform decisions on where investments are most needed to reduce injury and death. We measured exposure as miles walked or biked in California's 15 largest cities, using a validated model and data from the US Census, National Household Travel Survey, OpenStreetMap, and a statewide crash database. We performed linear regression with exposure and crashes, ranking cities by safety based on residuals. Higher positive residuals indicated less safe cities for active transportation. Including exposure shifted which cities had the highest safety risks for bicyclists and pedestrians. Safety differences were greatest in cities with high percentages of Hispanic residents, where crash-to-volume ratios showed unsafe conditions. Our method enables robust regional assessment of bike and pedestrian safety, allowing health departments and planners to identify where infrastructure investments can effectively prevent injuries and deaths, reduce health disparities, and create environments supporting active living. Our approach is scalable to major population centers nationwide, supporting evidence-based decisions that protect public health.