Cost analysis of the <Emphasis Type="Italic">R</Emphasis>-unloader queueing system

This paper deals with an unloader queueing model in which N identical trailers are unloaded by one or more unloaders. Theoretical solutions are obtained with the assumption of negative exponential distributions for trip times, unloading times, and finishing times. A cost model is developed to determine the optimal number of trailers. In order to evaluate the model robustness, simulation models are developed for three different distributions, exponential, second-order Erlang, and triangular. We demonstrate, through simulation results, that the unloader queueing model is sufficiently robust to the variations of probability distributions.