A Study on Green Two Echelon Vehicle Routing Problem with Simultaneous Pickup and Delivery

The growing population of cities, hence the demand for products and services, has increased the demand for urban logistics. The number of vehicles in urban circulation has risen in lockstep with the growth of logistics activities, as has air pollution as a result of the vehicles' fossil fuel usage. Thus, it is essential to consider vehicle loads on the arcs in order to reduce fuel consumption, which is directly proportional to greenhouse gas emissions, when planning logistics activities in the city. This paper considers a two-echelon vehicle routing problem with simultaneous pickup and delivery with load factor (2E-VRPSPD-LF) in which pickup and delivery activities are only carried out simultaneously in the second echelon. The 2E-VRPSPD-LF deals with obtaining vehicle routes on both echelons to minimize the total amount of fuel, which is determined by the driving distance and the total load of the vehicle. This study fills a gap in the literature by addressing 2E-VRPSPD-LF and providing a new perspective on city routing. We propose a mixed integer programming formulation to solve the 2E-VRPSPD-LF and strengthened with valid inequalities to obtain better lower bounds. The computational analyses of the mathematical model on test problems and a real-world problem in Turkey show that the green objective function has a significant impact on total fuel consumption.