Locomotive and wagon technologies vary widely, reflecting the range of goods to be transported (e.g. inter-modal, bulk or carload). They are also influenced by the physical characteristics of the lines and routes over which trains are operated and include ruling gradients, curvature, axle loads and varying adhesion conditions. Train length and weight is also influenced by available passing loops to minimise conflict with other faster traffic.
Freight train speed reflects the need to be able to integrate with other traffic and not create delays through inadequate acceleration and braking capabilities. Higher acceleration rates and cruising speeds require higher installed power and this comes at a cost.
Higher speed trains require higher installed power (~3hp/tonne gross) and this applies to container trains. Multiple locomotives, including locomotives located centrally within a train formation, can and are used in some national railways. Many nations use only single locomotives and this limits train length and weight. The choice of traction technology (diesel electric or straight electric) is largely dictated by the relative extent and inter-connectivity of electrified lines and the relative cost of this traction option compared with alternatives. Electrified operation is emissions free at the point of use.
Diesel locomotives are limited in terms of maximum power by the energy conversion capabilities of the engine/prime mover and related electric transmission system. Electric traction can draw large amounts of power through the catenary and regenerate in braking mode. Diesel traction cannot do this. Traction assets may be owned by the host railway or leased through deals with banks and manufacturers. Lease deals covering maintenance, operation, fuelling and crews have been developed.
Wagons also come in a mixture of designs and capabilities. Many are commodity specific (oil tankers, bulk aggregates, car carriers) and have specific features require to handle particular traffic commodities.
Wagons are key assets and need to be kept in active revenue generation (i.e. kept moving) as much as possible with minimal down time and related servicing and maintenance. Many wagons are in effect dumb assets with limited or no self-awareness of their technical and commercial/operational condition. This needs to be addressed to drive up asset productivity. Wagon utilization needs to be well planned to minimise dead time between commercial applications.
Container wagons can and do vary in size, weight, length and capability. Simple flat cars able to accommodate a mix of container sizes have been supplemented and in some cases replaced by specialist wagons able to accommodate high cube containers. Some wagons operate in semi-permanently couple sets. The use of twin stack container carrying wagons in North America has made rail much more competitive by effectively doubling the train payload per unit length of the train. This was a major boost to productivity but needed to be supported by adequate terminal handling capabilities, cargo priority planning and links to local trucking for last mile deliveries.