A study conducted by Massachusetts Institute of Technology for the Association of American Railroads has proposed the use of higher, shorter wagons to optimise application of heavier axleloads.

Drawing data from 22 sample coal train flows from across North America, researchers compared a standard 16m four-axle wagon with 30 tonne axleloads against various axleloads, wheel diameters, and three-axle trucks for a constant load density. Most combinations offered lower operating costs, but at the price of increased track maintenance charges. Overall the study confirmed that the 32 tonne axleload now being adopted for American heavy-haul corridors offered the optimum performance.

The study looked at a range of factors including the effects of heavier vehicles on line capacity and vehicle utilisation, and network application rather than a dedicated heavy-haul corridor.

According to MIT Senior Research Associate Carl Martland, the critical factor in maximising cost savings is the net capacity per train. Moving to shorter, wider and higher vehicles to suit the heavier axleload offers further savings in general merchandise trafffic. Optimising the vehicle design could lift net train capacity by 17% whilst cutting operating costs by 3 to 4%. o