Continuous Terminal–Vessel Routing for Automated Ro-Ro Finished-Vehicle Handling: An OSM-Based Three-Layer Network and Level-Aware Bidirectional A* Search

Finished vehicles are loaded onto and discharged from roll-on/roll-off (Ro-Ro) vessels by drivers who choose routes from experience. Automated handling requires continuous routes between storage-yard parking positions and on-deck stowage positions in both directions. This study represents the storage yard, the quay connection and the vessel decks as a single directed network built from OpenStreetMap (OSM) data. The route cost adds fixed penalties for turns, level transitions and ramp use to the travel time, which is reported separately. Because these penalties dominate the route cost, a lower bound on the level-transition penalties is incorporated into the A* heuristic, and routes are computed by bidirectional A* with an average potential and a sum-based stopping rule. On the Gwangyang Port testbed, the method returned the optimal route for all 15,000 origin–destination pairs and reduced the search effort by about one quarter relative to Dijkstra’s algorithm. Unidirectional A* with the same bound achieved a similar reduction, indicating that the gain derives from the heuristic rather than from the bidirectional structure. Compared with shortest-distance routes, the cost-based routes contained markedly fewer left turns at almost no additional travel time and remained stable over a wide range of penalty values.