multiple lines of covered hopper railroad train cars on tracks in trainyard

above axle bogie box bulk capacity cargo carriage carry cars coupled coupler couplings covered distance down economical freight from ground historic hopper hoppers janney limit line lines load logistics long looking material merchandise midwest move moving multiple rail railcar railroad rates raw rolling schedule secure ship shipment shipping slow states stock switch system time tonage tons tracks train trains trainyard transport transportation transporting travel united wagon weight wheels yard