Quantify relationships between bike network connectivity and bike safety: A comparative analysis of connectivity metrics conducted in two California cities

To motivate people to use bikes for transportation, cities are shifting their focus from constructing isolated bike lanes to building interconnected bike networks. The effectiveness of these networks is measured by their level of connectivity, specifically how easily individuals of all ages and abilities can reach their destinations by bike. While most researchers and policymakers hypothesize that well-connected bike networks will reduce crash risk by offering bicyclists extended protection from traffic, most studies find positive or null associations between network connectivity and bike crashes. This discrepancy may arise either from actual processes, such as increased ridership in high-traffic areas, or from variability in how connectivity is measured. Our study aims to understand relationships between bike safety and various connectivity metrics at the neighborhood level by deconstructing and comparing different metrics. We critique previous constructs of density-based metrics rely solely on bike infrastructure and introduce new density-based and routing-based metrics derived from low-stress networks. Using a negative binomial regression model, we examine the association between bike crashes and connectivity metrics across 125 block groups in Santa Barbara and Goleta, California. We find that increased density-based connectivity in both bike infrastructure and low-stress networks correlates with fewer crashes. In contrast, routing-based connectivity measures, which reflect bike access to key destinations, are positively associated with crashes. We conclude that different connectivity metrics can alter the direction of connectivity-safety associations. Our proposed metrics, which incorporate low-stress networks and routing algorithms, provide a more nuanced understanding of how connectivity is related to bicycling safety.