Vehicle routing problem with alternative links from the triple bottom line accounting perspective

As a result of diminishing natural sources and increasing global warming, environmental considerations are attracting more attention. In addition, today many firms are adopting a socially responsible management perspective. In this study, we analyze a vehicle routing problem (VRP) from the triple bottom line accounting perspective, considering financial, environmental and social objectives. In the literature, almost all studies about VRP consider only one link between two nodes in the network. However, in real life, more than one way can exist between two nodes, which may be different in length, duration or traffic conditions. One road might be longer but require less time due to traffic or speed limitations and result in less carbon emission or cost. Another road might be shorter but require a longer time, leading to conflicting objectives in terms of financial, environmental and social condierations. In our study, we develop a model to determine which alternative link to use between two nodes, depending on the model objectives and constraints, in addition to the routing decisions between the nodes. In this study, the minimum cost routing is considered as the financial objective, minimizing the CO2 emissions and gas usage are considered as the environmental objectives, and optimizing the driver working conditions/working hours, and minimizing the risks of accidents are considered as the social objectives. With these objective functions, we aim to determine which routes, and which alternative links should be used depending on the road properties, in addition to the speed choices at each link. We develop a mixed integer linear mathematical model for this problem and solve small sized instances using this mathematical model, for middle and large sized instances, we also propose a simulated annealing algorithm. We present the results of our detailed numerical studies and analyze the optimal solutions found under different settings. We extract the managerial implications of our results from the triple bottom line accounting perspective. Keywords: Vehicle routing, Alternative links between nodes, Mathematical programming, Simulated annealing.