Longest trains

The length of a train may be measured in number of wagons (commonly used for bulk commodities such as coal and iron ore) or in metres for general freight. On electrified railways, particularly those using lower-voltage systems such as 3 kV DC and 1.5 kV DC, train lengths and loads are often limited by traction and power supply constraints. Other limiting factors include drawgear strength, coupling systems, track curvature, gradients, and the lengths of crossing loops.

The development of distributed power—where locomotives are placed mid-train or at the rear of the consist and remotely controlled from the lead unit—has enabled the operation of very long freight trains, sometimes exceeding 6 kilometres (3.7 mi; 20,000 ft) in length. By distributing traction and braking forces more evenly throughout the train, this configuration allows for longer and heavier consists while reducing the risk of derailment, particularly on curves.