Multiple working


On the UK rail network, multiple working is where two or more traction units are coupled together in such a way that they are all under the control of one driver.
If the front locomotive of a pair in multiple has failed the driver can still control the rear locomotive for as long as air and electricity supplies are available on the failed locomotive.
In tandem is when more than one diesel or electric locomotive are hauling a single train and under the control of a driver on each locomotive.

Locomotives

In the early days of diesel locomotives in the 1960s, locomotives worked within their class. Locomotives from different manufacturers had varying methods of controlling engines or braking systems. If a train required more than one locomotive, an additional driver was needed, at extra expense.
Since then, locomotives have been built to work with other locomotives in the same code or system. Similar systems are assigned a coupling code, which is normally indicated on the front of the locomotive.
Early diesels were also fitted with communicating doors in the nose which allowed the secondman to access the train heating boiler of the rearmost locomotive. The doors actually saw little use and, as they frequently caused draughts in the cab, many of them were later welded shut.
Coupling codeSystemClass of locomotives
Blue StarElectro-pneumaticClass 15, Class 17, Class 20, Class 21, Class 24, Class 25, Class 26, Class 27, Class 31/1, Class 33, Class 37, Class 40, Class 44, Class 45 and Class 46, Class 73, Class 74.
● Red CircleElectro-magneticClass 16, Class 21, Class 28, Class 29, Class 31/0.
● Green CircleSome Class 47.
■ Orange SquareDiesel hydraulic - 1st useClass 22, D600 Warship
■ Orange SquareSymbol re-used for different systemClass 50
Red DiamondClass D16/1
Class 17
Red DiamondSymbol re-used for different systemClass 56, Class 58
Diesel hydraulicClass 22, Class 42, Class 43
Diesel hydraulicClass 35
SR EMU SystemClass 33/1, Class 73, Class 74, Mark One Electric Multiple Units, Class 442
Class 87, some Class 86ss
Class 43, Class 60, some Class 68s
TDM SystemClass 86, Class 87, Class 89, Class 90, Class 91, Push-Pull fitted Class 47, DBSO, DVT
AAR SystemClass 59, Class 66, Class 67, some Class 68, Class 70 & Class 73/9, plus several converted DVTs

Multiple units

First-generation

diesel multiple units had the additional problem of differing types of transmission. For instance, a Class 127 unit could be required to work in multiple with a Class 112 unit. For this reason, the drive selector on the Class 127 was fitted with positions marked "D, 3, 2, 1" to change the gears when working in formation with vehicles with mechanical transmission.
First-generation DMU coupling codes:
Coupling codeClass
■ Blue SquareMost units with mechanical transmission
Orange StarMost units with hydraulic transmission
Yellow DiamondDerby Lightweight
Red TriangleDerby Lightweight
O White CircleClass 126

Second-generation

Most second-generation units built by British Rail were designed to use the BSI multiple working system, including members of the 14x Pacer and 15x Sprinter families. Some post-privatisation trains such as the Class 168, 170 and 172s were fitted with BSI couplers enabling them to operate in multiple with older stock, while other incompatible systems emerged. Examples included Dellner-couplers fitted to Class 171, 220, 221, 222, 350, 360, 375, 376, 377, 390, 700 and 710s while Scharfenbergs were fitted to Class 175 and 180s. Franchise changes and stock reallocation means that many train operating companies use fleets with a number of incompatible multiple working systems.