Five production lines supply their products in boxes to a transport system which contains 4 side conveyors and one main conveyor. Boxes on the main conveyor have priority over boxes on the side conveyors. A number of questions regarding the transport system’s capacity is asked: what point denotes the limit of the production increase? Where do problems resulting from a production increase appear? Does increasing the speed of the conveyors have any effect? This is a typical example of a transport system with accumulating conveyors.