This paper proposes an optimal vehicle dispatching policy for transportation disruption. This policy determines the optimal vehicle capacity and dispatching time along a route. Transportation demand includes wiener demand and the unusual demand disruption, i.e. emergency evacuation. The cost function is consisted of waiting time cost and transporting cost. Sufficient conditions have been given with proof by quasivariational inequalities. Both finite planning horizon and an infinite horizon cases have been discussed. This proposed method can be applied into various scenarios, such as mass transit dispatching, freight transportation, aircraft shuttle scheduling and so on.