Built Environment, Perceived Usability, and Low-Carbon Mode Choice Across Different Trip Purposes

Existing studies often examine associations between the built environment (BE) and low-carbon mode choice using aggregated travel outcomes, with limited attention to how these relationships vary across trip purposes. Using a final analytical sample of 855 respondents from Xi’an, China, this study integrates random forest (RF), SHapley Additive exPlanations (SHAP), partial dependence plots (PDPs), principal component analysis (PCA), and structural equation modeling (SEM) to examine purpose-specific BE importance, nonlinear response patterns, and perception-mediated pathways across six trip purposes. These include commuting, education, maintenance activities involving shopping and routine daily services, healthcare, recreation involving cultural, fitness, and entertainment activities, and outdoor leisure involving parks, squares, and scenic areas. The results show substantial heterogeneity across trip purposes. RF models achieved area under the receiver operating characteristic curve (ROC-AUC) values ranging from 0.742 to 0.861, while the most important BE dimensions differed across purposes. Nonlinear associations also varied in form and range across trip purposes, including an apparent turning point at approximately 200 m for the distance to the nearest bus stop in commuting trips, beyond which the predicted probability of low-carbon travel declined. SEM results further showed that perceived BE mediated only specific BE–travel pathways, with partial mediation identified for PCA3 in maintenance trips and PCA2 in recreation trips after accounting for community-level clustering. No full mediation was identified. These findings show that BE–travel relationships vary in environmental importance, nonlinear response, and perception-mediated pathways across daily activities. The results can help planners identify purpose-specific environmental priorities and develop more targeted community-scale interventions for sustainable transportation.