 | ||
Multiple working is a term used on the UK rail network to describe the practice of having more than one diesel or electric locomotive hauling a train under the control of one driver (multiple-unit train control).
Contents
Terminology
Multiple Working is the term used in the UK where more than one operational diesel or electric locomotive are coupled together under the control of one driver. The term can also apply when diesel or electric multiple unit trains are coupled together and also under the control of one driver. 'In tandem' is the term usually used in the UK when more than one diesel or electric locomotive are hauling a single train and under the control of a driver on each locomotive.
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.
Locomotives
In the early days of diesel locomotives, locomotives worked within their class (i.e. two locomotives of the same class could work together but not with other classes). 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.
First-generation
First-generation diesel multiple units had the additional problem of differing types of transmission. For instance, a Class 127 unit (hydraulic transmission) could be required to work in multiple with a Class 112 unit (mechanical transmission). 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:
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. Later units, post-privatisation ones in particular, saw a number of different, incompatible systems re-emerge. Examples include the Dellner-coupled Class 220, 221 and 390, originally used by Virgin Trains, and the Scharfenberg-coupled Class 175 and 180, originally used by First North Western and First Great Western respectively. Franchise changes and stock reallocation means that many train operating companies use fleets with a number of incompatible multiple working systems.