A state-of-the-art review of underground logistics systems: Research trends, application modes, planning approaches, and future directions

Underground logistics systems (ULS) encompass a series of transformative technologies and engineering entities designed to enable automated freight transportation within and around cities. Featured by clean energy, all-weather operations, and high capacity, ULS are seen as promising solutions to mitigate “big city diseases” and improve logistics efficiency and sustainability. Previous studies and practice on underground freight transport have produced rich insights and experience for scaling up the system implementation, however, little effort has been paid to frame the state-of-the-art knowledge in this field. This paper performs a systematic literature review to synthesize the concepts, prototypes, and methodologies of ULS that have being explored in recent decades. Our investigation focuses on three aspects: (i) trends in academic publications and key research topics, (ii) potential application areas and modes, and (iii) theories and approaches to system planning, management, and future expansion. The underground system forms and constituents fitting with diverse needs for the intermodal logistics (e.g., port containers) and urban delivery (e.g., metro freight and waste collection pipelines) are summarized. Based on literature findings, we elaborate the critical issues in ULS implementation at strategic, tactical, and operational levels, therein, three major research themes are analyzed, i.e., the interaction between ULS and cities, the strategic agendas of ULS programs, and the decision support tools for ULS planning, design, and operations. Finally, the current knowledge gaps and lessons learned from practice are identified. Novel insights are delivered to the future development of ULS, along with directions for the theoretical innovation in this emerging field.