Because of congestions in traffic a precomputed shortest route (path) of a vehicle from an initial location to a prescribed one cannot be always adhered. In such a case it is necessary to change it flexibly. However, to save cost the new route should be chosen in virtue of prescribed rules. The place/transition Petri nets, more precisely its simpler kind named as state machines (SM), is utilized here to model the real structure of the possible routes area. An algorithm for finding the least-cost firing sequence of SM transitions is proposed. To extend the approach on adjacent areas the agent-based approach is drawn too.