A Multicommodity Urban Evacuation Problem
The multicommodity problem that will be introduced in this chapter is formulated as a mixed-integer model where the number of lanes are represented by integer variables. It incorporates the commodities vehicles of evacuees and buses. The two-staged heuristic approach solving the pattern-based formulation of the urban evacuation problem turns out to generate feasible solutions faster than the relaxation-based heuristic approach that solves the mixed-integer formulation of the urban evacuation problem. With the two-staged approach it is possible to generate feasible solutions of problem instances which cannot be solved with the relaxation based approach. The computational study comparing both approaches is restricted on one-way streets (see Sect. 6.3). But for the multicommodity problem, we want to allow two-way streets. One reason is that buses, which drive to assembly areas to pick up evacuees, travel opposite to the evacuation flow.