The more recent plan combined rail and lake-vessel delivery of coal to satisfy the plant's requirements. Costly delays were occurring. To alleviate the problems, Detroit Edison considered the addition of a second multimillion-dollar unloader system. Although a simulation model of the entire rail-coal movement system was available, an analytic model was built to focus on the unloader. Reducing the frequency of unloader breakdowns, Reducing the repair time, and Changing the cycle between the mine and the power plant.
All trains are the same size.
A train can wait at the facility while an unloader is being prepared. When two unloaders are broken, two crews work independently on them. When one unloader is broken, only one crew repairs it. A train that is in a facility when one unloader breaks down is rerouted to the other unloader facility. Data were collected from records on breakdowns, trip-completion times, the use of a single unloader and two unloaders.