two-objective optimization

This paper presents a two-phase approach to design an optimal personnel transportation network for the Bistoon Power Plant. In the first phase, a mathematical model of location-allocation for locating bus stops and allocating staff to bus stops has been formulated with the objective of minimizing the total walking distance for staff. For the second phase, a mathematical model of location-allocation-routing with time window for selecting vehicles with the appropriate capacity for each route, locating the parking places (start nodes), vehicle routing, and trip scheduling is discussed with the two objectives of minimizing transportation costs and minimizing the maximum travel time of staff to ensure fairness among staff. One of the features of this study is the consideration of the distance between vehicle parking areas and the first demand nodes on each route in order to locate parking areas. Other expected side benefits of the implementation of this research are decreasing the total travel distances, traffic congestion, and air pollution. Despite the large number of nodes and data of the case study, the proposed mathematical models are solved by the exact solution method. In order to solve the two-objective model, the augmented epsilon constraint method has been used to find the Pareto solution set.