Do you know what “double heading” means? Or why multiple-unit traction can take different forms? Why for example both traction units are placed at the front of a freight train and then at other times with one locomotive pushing from behind?
When forming trains, we must not only consider the freight wagons, but also the traction vehicle. For each transport route that we run freight trains on, there is a so-called “route class” that describes the track characteristics and loading of the railway lines. It indicates the maximum permissible total weight of a freight wagon.
Furthermore, there are different traction units that have different trailing loads due to their technical equipment. The loading of the traction units, the coupling hook load limits and the maximum “banking” (pushing) load can be taken from the infrastructure schedule support tables. The topographical conditions of a country often require two, three or even four traction vehicles to convey a freight train from A to B over certain sections of track. That is why there is always talk of triple-heading or even multiple-unit traction.
Running a train with two traction units can take different forms – e.g.:
Tandem operation – the two locomotives are connected together synchronously and controlled by one traction unit driver.
Pilot engine – the technical equipment of the double header requires that locomotives 1 and 2 are each controlled by a traction unit driver.
A second locomotive is attached as a “bank engine” to the rear of the train if the coupling hook of the pulling traction unit is not strong enough. This second locomotive acts as a pusher engine for the freight train. This use requires a traction unit driver in each locomotive.
Origins of double heading
Incidentally, double heading was first used in 1883, albeit in purely mechanical form at that time. The exhibition railway built by Siemens & Halske for the International Electrotechnical Exhibition in the Vienna Rotunda had a connecting rod between the two railcars, which made simultaneous control possible. The first electric version of the double traction was used in 1895 on the first Budapest metro line, which was also equipped by Siemens.
Since 2017, Rail Cargo Group has been operating trains that are equipped with reinforced couplers and buffers. These allow a fifty percent higher trailing load to be pulled. With a resulting reduction in the number of traction units required.