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British Rail Class 314 alternating current (AC) electric multiple units (EMU) were built by BREL at York works from 1978 to 1979. They were the second variety of British Rail's then-standard 1972 design for suburban EMUs, which eventually encompassed 755 vehicles and five Classes (Class 313/314/315/507/508). Able to operate from 25 kV overhead line only, the fleet works inner-suburban services on the Strathclyde Passenger Transport rail network in Central Scotland.

Description
Sixteen Class 314 3-car units were introduced in late 1979 to operate on the then newly opened Argyle Line, and were used on both this and the North Clyde Line routes until 2002, when the scrapping of the elderly Class 303 stock led to much stock cascading within the SPT network. The Class 314 was based on the experimental Class 445 or "PEP" unit, the design of which spawned the sister Class 313 and Class 315 units which are used extensively in the London commuter area.

In line with the other PEP-based classes, the Class 314 units consist of two outer motor cars with an unpowered trailer vehicle in the middle, giving a technical description of DMSO+PTSO+DMSO. The coaches are of integral aluminium alloy construction based on a steel underframe. Each 3-car set can seat up to 220 people, and following the standard practice in the Glasgow suburban sector, peak time services can be formed by operating two units in multiple to form a 6-car train.

Current operations
Since 2002, they are mostly found working on the Cathcart Circle Lines (including the services to Newton and Neilston). A small number of units also usually work Inverclyde Line services to Wemyss Bay and Gourock, particularly during peak hours.

The Class 314 units are now the oldest on the SPT network, and are unique in that they have not yet been internally refurbished (the leading motor coach of unit 314203 was replaced in 1992 by an ex-Class 507 coach after the original was destroyed in the Newton rail crash and differs from the other units due to its blue interior compared to the yellow of the others), whilst units 314208 and 314212 were severely damaged when they were "drowned" in an Argyle Line tunnel following the River Kelvin bursting its banks in torrential rain at the end of 1994.

In May 2006 a limited mechanical overhaul programme to the units was initiated, with upgraded door mechanisms and upgrades to the electrics and Automatic Warning System (AWS) equipment. 314202 lost its classic SPT orange/black livery (the last remaining multiple unit in Scotland to carry the old livery) in favour of the current carmine/cream scheme when it passed through Glasgow Works at the end of November 2006.

314206 entered Glasgow Works on 20 July 2007. This is the final unit to receive a major overhaul pending a decision on the future of the Class 314 units.

Future
314206, the last unit in the current overhaul programme, is currently in Glasgow Railcare. A decision is due soon on possible replacement of the Class 314 units, and as such, all 314s have not been fitted with on-train monitoring recorder (OTMR) equipment and have been granted a derogation pending a decision on the future of the fleet.

There has been much speculation over the future of the Class 314s - it was suggested that they may be replaced in a stock cascade initiated by converted Class 458 units (the direct current (DC) version of the Class 334 "Juniper" units already used elsewhere on the SPT network). However, it has since been revealed that the Class 314s will continue to be in service until at least 2015.

In September 2008 the Scottish Government's agency Transport Scotland announced that all ScotRail trains (including from the Strathclyde Partnership for Transport) would be eventually repainted in a new, blue livery with white Saltire markings on the carriage ends. This will include the Class 314s.