From surface to subterranean: mapping two decades of passenger–freight synchronization research

• This study reviewed research on transportation synchronization of passenger and freight. • A new classification was proposed for transportation synchronization. • The classification is based on the infrastructure and the type of synchronization. • Several suggestions were provided for future studies on transportation synchronization. • An analysis showed the lack of research on surface-underground integrated logistics. Among the growing challenges of urban logistics caused by the expansion of e-commerce, transportation synchronization, as an innovative solution, aims to optimize traffic flows and enhance service quality for users. This study systematically reviews recent research on transportation synchronization, analysing 93 primary studies and 6 additional methodological/contextual references used for methodological justification and contextual analysis, covering the period from 2001 to 2024. The review focuses on synchronization in synchronization constraint domain, including passenger and freight transportation. For this purpose, studies on transportation synchronization were categorized by synchronization type, and studies on passenger and freight transportation were classified according to transportation infrastructure. After reviewing and summarizing the classified papers, recommendations for future research on passenger and freight transportation synchronization are proposed. Overall, this review reveals that most studies related to transportation synchronization have targeted passenger and freight transportation operations in surface or underground logistics, while few studies address synchronization in the integration of surface and underground logistics for passenger and freight transportation.