Ethics-Aware Multimodal Accessible Transit Design: Synergistic Optimization of Equity and Efficiency

Abstract

In the pursuit of operational efficiency, urban transit systems frequently overlook equity across social groups, resulting in substantial accessibility disparities for vulnerable populations such as older adults, people with disabilities, and low-income residents. Although transport equity has gained increasing scholarly attention, existing research rarely embeds explicit ethical principles into the design and optimization of complex multimodal networks. In particular, the quantification and improvement of transfer accessibility remain underexplored, despite transfers being critical bottlenecks in multimodal travel chains. To address this gap, this study proposes an ethics-informed framework for multimodal accessible transit design. Drawing on and operationalizing John Rawls’s Difference Principle, the framework adapts this normative concept to a networked transport context by formulating an optimization objective that prioritizes improvements in accessibility for the most disadvantaged groups. Rather than maximizing aggregate accessibility, the model seeks to enhance the minimum accessibility level within the system, thereby aligning network design with distributive justice principles. Using a major metropolitan area as a case study, the research constructs a comprehensive, reproducible multimodal transit network model integrating metro, bus, and bike-sharing systems. The model relies exclusively on publicly available data sources, including open transit schedules and stop data (e.g., GTFS or official timetables), open points-of-interest (POI) datasets, and aggregated demographic statistics. This data integration enables transparent modeling of travel times, transfer processes, and opportunity distributions across space. A key methodological contribution is the development of a transfer accessibility index that explicitly incorporates both physical barriers (e.g., walking distance, vertical circulation constraints) and temporal barriers (e.g., waiting time, schedule synchronization). By embedding this index into the optimization framework, the model captures the equity implications of transfer design—an often-overlooked dimension of accessibility measurement. Numerical experiments reveal that, under realistic conditions characterized by uneven spatial distribution of opportunities, conventional utilitarian optimization strategies tend to exacerbate accessibility inequality. In contrast, the Rawlsian difference-principle-based design substantially improves distributive outcomes, increasing accessibility for the most disadvantaged groups by more than 35%, while incurring a 10–15% reduction in overall system accessibility. These findings illustrate a measurable equity–efficiency trade-off and provide quantitative evidence of the redistributive potential of ethics-guided planning. Moreover, the results indicate that targeted improvements to transfer nodes represent a particularly effective lever for enhancing overall transport equity. Because transfer points function as critical connectors within multimodal systems, their design disproportionately affects accessibility outcomes for vulnerable users. Overall, this study contributes a theoretically grounded and operationally implementable methodology for embedding ethical reasoning into transit planning. By translating the difference principle into a formal optimization model and demonstrating its empirical implications, the research offers urban planners and policymakers a practical pathway for systematically integrating equity considerations into multimodal network design. In doing so, it advances the development of more inclusive and sustainable urban transit systems that balance efficiency with distributive justice.