Adaptation of some vehicle fleet mix heuristics

Standard models used for the combined vehicle routing and vehicle fleet composition problem use the same value for the unit running cost across vehicles. In practice such a parameter depends on several factors and particularly on the capacity of the vehicle. The purpose of this paper is to show simple modifications of some well known methods to allow for variable running costs; and also to assess the effect of neglecting such variability. Interesting numerical results, measured in terms of changes in total cost or/and fleet configuration, are found at no extra computational effort.