MULTIPLE WORKING

'Multiple working' is a term used on the UK rail network to describe control systems that allow locomotives and multiple units of different types to work together.

Contents

Locomotives

Multiple units

References

Locomotives

In the early days of diesel locomotives, locomotives worked within their class (ie, 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.

'Code or system'	'Class of locomotives'
AAR System	Class 59, Class 66 and Class 67.
Blue Star Coupling Code	Class 20, Class 24, Class 25, Class 26, Class 27, Class 31, Class 33, Class 37, Class 40 and Class 45.
Green Circle Coupling Code	Some Class 47.
Orange Square Coupling Code	Class 50.
Red Diamond Coupling Code	Class 56, Class 58.
SR System	Class 33/1, Class 73, Mark One Electric Multiple Units.
AC electric locomotives	Class 87, some Class 86s.
Within own class only	Class 43 InterCity 125, Class 60.

Multiple units

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 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.^[1]
Many types of second-generation DMUs are compatible with each other and may work in multiple. These include classes 150, 153, 155, 156, 158, 159 and (with certain restrictions) 170.

References

1. Description of the Class 127s The Railcar Association