The vehicle routing problem
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The Vehicle Routing Problem (VRP) was originally defined in 1959. The model used was a simple one that was appropriate to the software and hardware systems of the time. Since then many hundreds of papers have been written addressing the VRP and variants on it. Almost all are based on the original model or extensions of it. In particular notions of demand and the vehicle are adopted, seemingly without question. Capacity constraints, including volume, are considered to be linear. But this model does not match that used in commercial software -- such as Transport Management Systems (TMS). In particular the concepts of Order and separate resources corresponding to the Driver, the Tractor Unit and the Trailer in the TMS need to be properly addressed to solve a variety of common real-world problems. This paper shows, through examples taken from Optrak customers, how without these concepts some common aspects of the problem cannot be addressed and how any attempt to map them onto the standard VRP formulation will result in major inaccuracies in the model and hence the usefulness of the results.