Route Optimisation for Winter Road Maintenance using Constraint Modelling

Abstract: Planning of routes for the many kinds of road maintenance problems is essential. These problems can be generalised to the vehicle routing problem, where a num- ber of available vehicles should be assigned to objectives in an optimised order. With different kinds of winter-based maintenance tasks come many variations of the problem, making the flexibility of an optimisation system an important aspect. The problem is approached using constraint programming technology with the modelling language MiniZinc. A model is presented for route opti- misation of winter road maintenance related problems. The model has been tested against an existing system written in C# using guided local search as search strategy, in terms of quality of the solution and solving time. Several back-end solvers have been tested with the model in a black-box manner; CPX Opturion, Gecode, or-tools, and OscaR/CBLS, where or-tools performed well compared to the others. The advantages of using constraint modelling with MiniZinc are shown when the problem specifications are not clear beforehand, since adapting a model for new scenarios is done with little effort. However, the presented model can not compete in terms of solving time when the problem size increases. A proposed solution to this is to cluster objectives together and generalising the problem, making the problem sizes smaller.