We present a Decision Support System (DSS) for co-modal transportation. The DSS answers multiple route planning requests in a co-modal setting with vehicle preference and conflicting criteria, e.g., costs, time, and gas emissions minimization. The DSS architecture is based on the inherently distributed multi-agent systems framework that allows the decomposition of the route planning problem into multiple simpler tasks. A genetic algorithm is employed to obtain the optimal user-vehicle-route combinations according to the users preferences. The DSS is tested simulating itinerary requests with conflicting preferences in Nord Pas de Calais (France).