Ship Traffic Optimization for the Kiel Canal

AbstractIn “Ship Traffic Optimization for the Kiel Canal,” Lübbecke, Lübbecke, and Möhring develop graph-based models and algorithms to solve a practical traffic scheduling problem. It arises in the operational planning of bidirectional traffic where vehicles can pass each other only at dedicated locations—e.g., vessels that navigate narrow waterways. The authors provide decision support for the particular planning problem at the German Kiel Canal, the world’s most frequented artificial waterway, but their findings generalize, e.g., to scheduling trains on a stretch of single tracks or collision-free routing of robot arms. Mathematically, these planning problems expose a rich combinatorial structure. Ideas from quickest path algorithms and job-shop scheduling are integrated to handle all practical constraints at a high level of detail. The modelling does not need any time or space discretization. The software tool developed during the study was also used to assess strategic options of enlarging the canal.We introduce a hard practical optimization problem, the ship traffic control problem (STCP). We study it at the Kiel Canal, which is the most frequented artificial waterway in the world. The canal is operated bidirectionally, but large ships can pass each other only in sidings. Decisions must be made about who is waiting for whom, where, and for how long, subject to a multitude of operational constraints. The objective is to minimize the total waiting times of all ships. This problem generalizes train scheduling on a single-track network. We integrate algorithmic ideas from collision-free routing of automated guided vehicles. This leads to a unified view of scheduling and dynamic routing that may serve as a prototype for scheduling bidirectional traffic with passing conflicts. We implement a traffic control tool that uses our combinatorial algorithms and perform a computational study on traffic data from the Kiel Canal. Our tool produces schedules that significantly improve over manual planning and were approved by expert planners. As traffic volume and vessel sizes are projected to significantly increase, the canal is planned to be enlarged in a huge project. Our tool was used to select from a variety of enlargement options. The enormous level of detail in our model ensured that the chosen construction scenario actually constitutes a remedy to the impending inoperability of the canal.