One stone, two birds: Exploring the intermediary role of car ownership in the link between built environment and car crashes

While enhancing traffic safety and reducing car ownership are central to neighborhood design, these two goals are often treated as separated and unrelated policy areas. There has been little empirical examination of the inherent connection of car ownership and car crashes embedded in contemporary neighborhood design practices, leading to divergent or even contradictory design approaches. We address this gap by leveraging emerging geospatial data and the structural equation modeling (SEM) approach to explore the intermediary role of car ownership in the relationship between the built environment and car crash incidences, adjusting for traffic exposure, using a case study of Chengdu, China. By comparing multiple conceptual models, we found that the built environment influences automobile-involved crashes both directly and indirectly through the positive and parallel mediation of car ownership and traffic exposure. Specifically, transit-oriented development (TOD) design strategies, including mixed land use, balanced job-housing ratio, and good access to public transit, emerge as effective design solutions that can “kill two birds with one stone” by reducing car crashes through lowering car ownership. Additionally, we also found that car-rich neighborhoods are not necessarily places with higher traffic exposure. Instead, the negative externalities of car ownership, such as heavy traffic exposure and increased traffic safety, may be transferred to car-deficient neighborhoods due to elevated traffic exposure, revealing a “hidden” transport safety equity issue, largely overlooked in the policy arena. Tackling the challenges of growing car ownership and subsequent road accidents requires integrated planning efforts. Our findings highlight transit-oriented development as a promising design solution that effectively and simultaneously reduces car ownership and car crashes. Furthermore, our research calls for greater recognition of the latent transport equity issue, where the negative externalities, such as automobile-involved crash incidences and vehicular exposure, are unevenly distributed between car-rich and car-deficient neighborhoods.