Research Progress and Trends of Integrated Passenger–Freight Transportation in Urban Rail Transit

To systematically review the research progress in integrated passenger-freight transportation in urban rail transit, 141 publications were used as the sample. The publications were retrieved from the China National Knowledge Infrastructure (CNKI), Wanfang Data, and Web of Science between January 2003 and May 2026. Statistical analysis of the literature, keyword co-occurrence analysis, and content synthesis were combined. Research hotspots, practical characteristics, and existing problems were identified, together with a comparative analysis of representative practices in China and abroad. Research results show that research in this field has grown rapidly since 2018, with metro systems as the main research object. Research hotspots center on network facility location and routing optimization and system operation scheduling. The former has expanded from separate facility location or routing optimization to integrated location-allocation-routing decisions. The latter has expanded from capacity allocation under a fixed passenger timetable to coordinated optimization of train formation, timetabling, and freight-flow allocation. Operations research methods remain dominant. Simulation is mainly used for parameter es-timation and plan validation. Machine learning has seen limited application and is used primarily for demand processing and auxiliary assessment. Current research has several limitations. Freight demand lacks empirical calibration, and the relationships between operational capacity and planning and scheduling decisions have not been adequately examined. Task adjustment under disruptions and machine-learning-assisted solution methods remain underexplored. Facilities and equipment lack validation under actual operating conditions. Safety standards specific to integrated passenger-freight transportation have yet to be established. Mechanisms for multi-actor coordination and intermodal connections remain incomplete. Operating practices have gradually shifted from early dedicated systems to the reuse of existing lines. Recent pilot projects in China mainly employ single-line freight hitching services or shared passenger-freight carriage modes. Their sustained operation depends primarily on stable freight demand, economic viability, safety boundaries, and policy support. Future research should focus on network planning based on empirically calibrated demand and accounting for operational capacity. Dynamic scheduling of freight tasks and intelligent solution methods under disruptions should be developed. Standards for cargo admission, transport safety, and facility retrofitting should be improved. Integration of rail transport with ground and low-altitude delivery and multi-actor collaborative governance should be strengthened.