Synchronization in synchromodality

•Review literature on synchromodality and clarify its synchronization concept.•Identify three types of synchronization in synchromodality.•Review methods for resolving synchronization problems.•Analyze challenges in synchronization and suggest future research directions.•Present integrated framework for understanding synchronization in synchromodality. One of the stepping stones towards the physical internet is synchromodality, which enables a seamless, flexible, and resilient interconnected network for door-to-door service. As its name suggests, synchronization is the core of synchromodality, but its concept is not yet clearly understood. This paper presents a classification of the literature on synchromodality based on proposed types of synchronization and discusses synchronization methods. Within the complexity of synchromodality, challenges in synchronization are recognized, resulting in several emerging issues. We recommend future research directions to address under-studied issues, highlighting the importance of multi-agent systems with learning for real-time decision making. Additionally, an integrated framework is developed to provide a comprehensive understanding of how synchronization works among various elements in a synchromodal transportation system.