The length of a train is measured by the no of wagons containing bulk loads such as ore, oil etc. that are attached to the main locomotive.
The length of a train and the load bearing capacity of the wagons can be limited on electrified rail gauges which are of a lower voltage rating such as 3000V DC or 1500V DC as they face issues with traction power.
Elevation changes, curves and bends along the route, loop lengths, couplings and draw gears can also be limiting factors to the length of a train. It is not very uncommon for a length of a freight train to have an average length of 2000 meters.
Longer lengths can also be achieved with the help of distributed power units, which can stretch the overall length to more than three or four times the average length, i.e. up to 8000 meters.
The main advantage of using distributed power systems is that they enable much longer and heavier loads to be carried across without the risk of the train derailing from the stress of pulling these long wagons along steep curves.
Adding a locomotive in between the freight wagons also aid in pulling the wagons more efficiently with efficient weight distribution among more than one locomotive. So without further ado, here is the list of the 10 longest trains in the world.