The problem is solved under the following constraints
1. Each node is visited only once by a single vehicle.
2. Each vehicle must start and end its route at the depot.
3. Total demand serviced by each vehicle can not exceed its capacity.
4. The travel time for each vehicle cannot exceed an allowable value.
5. The mean velocity of travel for all vehicles is constant.
6. The fleet is heterogeneous and there are three types of capacity as follows: small, medium, and large for
vehicles. Also, the cost of each type of vehicle is fixed.