The British Rail Class 313 is a dual-voltage electric multiple unit (EMU) train built by British Rail Engineering Limited's Holgate Road carriage works between February 1976 and April 1977. They were the first production units that were derived from British Rail's 1971 prototype suburban EMU design which, as the BREL 1972 family, eventually encompassed 755 vehicles over five production classes (313, 314, 315, 507 and 508). They were the first second-generation EMUs to be constructed for British Rail and the first British Rail units with both a pantograph for overhead lines and contact shoe equipment for supply. They were, additionally, the first units in Britain to employ multi-function automatic Tightlock couplers, which include electrical and pneumatic connections allowing the coupling and uncoupling of units to be performed unassisted by the driver whilst in the cab.
The Class 313 units were the oldest EMUs operating on the National Rail network in Great Britain prior to their withdrawal in 2023, having entered service in 1976. However, the even older 1972 Stock and 1973 Stock are still in service on London Underground.
Background
Two new fleets were ordered as part of the electrification, authorised in 1971, of suburban services on British Rail's Great Northern route between and , via on the East Coast Main Line and via on the Hertford Loop Line. For outer-suburban servicesthose making limited stops over the length of the routea fleet of 49 units were procured as derivatives of the proven design. The Class 313 fleet was correspondingly ordered for the inner-suburban servicesthose making frequent stops between London and Welwyn or Hertford.
An integral component of the electrification programme was BR's acquisition from London Underground of the Northern City Line, which had been built at a size sufficient for mainline trains and which provided the most direct route between , on the existing Great Northern route, and in the City of London. Following completion of the electrification to Welwyn and Hertford, the London terminal for all inner-suburban services would switch from King's Cross to Moorgate, reducing the number of train movements at the former station enough to permit the remodelling and subsequent electrification of the complicated approach tracks. The Northern City Line tunnels, however, were still not large enough to be fitted with the same overhead line electrification system used for the rest of programme, and were instead configured to use the system standard on BR's Southern Region. This in turn required that a new design of EMU be developed for the Class 313 order, as none capable of running on both systems existed at the time.
Given this requirement, the opportunity was taken to further develop the Class 445 and 446 prototypes that had been produced by British Rail Engineering Limited in 1971, and which were considered by BR to be "the basis of all [its] future suburban stock". As these prototypes had been configured for use only on third-rail electrification, a new intermediate trailer carrying a pantograph and AC to DC transformer was built and inserted into the two-car Class 446 prototype, which was then tested on AC-electrified track for six months in 1975. This three-car arrangement, with driving-motor vehicles 'sandwiching' the trailer carrying the AC collection equipment, was subsequently adopted as the basic layout for the Class 313 design.
Description
Given that the need to use the Northern City Line tunnels, Class 313 units are built to a slightly smaller loading gauge than conventional trains. They are of standard length and width, but the roof is lower, most noticeable due to the lack of a "well" for the Stone Faiveley AMBR pantograph on the centre coach. They have to comply with regulations for underground trains, such as having doors at each end of the train for evacuation onto the tracks, and when on 750 V DC supply the traction supply for each motor coach is separate, whereas on conventional 750 V DC trains each coach in a unit is linked by a 750 V bus line. Due to this, each motor coach has shoe gear on both bogies, whereas normally it would only be on the leading bogie. They are fitted with trip-cocks that are struck by a raised train-stop arm at red signals and will apply the brakes if the train passes one.