Do Roads Create Crime Boundaries? Modeling Crime Rate Disparities Across Adjacent Communities

Crime rates often change abruptly across the borders of adjacent communities, yet the mechanisms producing these localized disparities remain poorly understood. This study develops a boundary centered analytical framework to examine how roadway network permeability and boundary land use context jointly shape crime rate differences between neighboring areas. Using incident level crime data from six US cities, we apply crime informed community detection to identify approximately 2,000 adjacency boundaries and analyze crime disparities using nonlinear descriptive models, regressions, and SHAP assisted machine learning diagnostics. Results reveal a nonlinear relationship between permeability and crime disparities in which gaps are largest under low connectivity, narrow rapidly at moderate connectivity, and weaken or diminish at high connectivity. Infrastructure barriers and vacant or industrial land create boundary vacuums associated with persistent and volatile violent crime disparities, whereas commercial corridors amplify property crime disparities through increased opportunity exposure. Overall, violent crime patterns reflect insulation produced by physical and land use barriers, while property crime patterns reflect exposure to target rich environments. These findings position urban boundaries as a critical ecological unit for understanding micro scale crime divergence and offer actionable insights for place-based security interventions, resource allocation, and applied models linking to localized crime dynamics.