The London Underground D78 Stock operates on London Underground's District line, except the Wimbledon to Edgware Road service. Following the withdrawal of the C Stock in June 2014, these are now the oldest subsurface trains in service on the London Underground. The first units were withdrawn in January 2015 with all due to be replaced by S Stock by spring 2017.
The D stock was ordered in 1976 to replace the pre-war CO/CP Stock and post-war R Stock on the District line. Seventy-five six-car trains were built by Metro-Cammell, Birmingham, the first entering service on 28 January 1980 with final delivered in 1983.
The stock consists of six-car trains, as opposed to the seven-car trains of CO/CP and R Stock, whose cars were shorter: under normal operation, each train consists of two 3-car units, and 20 of the units are double-ended to allow 3-car operations under exceptional circumstances. The traction motors are the same LT118 type as on 1973 Tube Stock, but the bogies are different. With single-leaf doors and transverse and longitude seating, the style is very similar to 1983 stock on the Jubilee line.
The stock brought many innovations. The rubber coil suspension meant a smoother ride for passengers. The driver's cab is more ergonomic, the seat swiveling to move forwards, backwards, up or down. The dead man's handle is replaced by a joystick that needs to be twisted for the dead man feature, and moved fore and aft for motoring and braking. There is a Train Management System replacing the original Train Equipment Panel that highlights faults to the driver.
The most noticeable difference between the stock and earlier trains is that the doors are single leaf. Originally, passengers pressed door-control buttons to open them. Posters explaining how to operate the doors were put up around Tube stations in English, French and German when the stock was introduced. The stock had a "POGO" switch (Passenger open/Guard's open) that could switch control of the doors from passengers to the guard (when the stock was introduced, the guard controlled the doors from the rear cab). While this function proved useful at above-ground stations and termini (especially in winter), station dwell time was significantly increased, and passengers had trouble getting used to the new system, not knowing how to open the door. By the late 1990s, the control of the doors went to the driver, but the buttons remained until they were removed on refurbishment between 2004 and 2008.
At over 18 metres (59 ft), the cars are the longest on the Underground. The windows had to be modified because of overheating when new, with pull-down opening windows installed in each car.
The stock is used on the District line, except the High Street Kensington-Edgware Road section, because the platforms are not long enough there for D stock.
Between April 1985 and May 1987, the stock operated the East London line service in three-car formations, there being enough stock spare because of reduced services on the District line. This allowed A60/62 Stock to be sent for One Person Operation (OPO) conversion. The A60/62 stock took over the service again in 1987.
The stock is due to be replaced by S Stock in 2016. It is being replaced about 15 years short of its intended lifespan, as a consistent new fleet will allow for frequencies to be increased and will reduce maintenance costs.
In July 2011, Harrogate Chamber of Commerce proposed to use the stock on the Harrogate Line from York to Leeds via Harrogate to increase capacity. Stations in the Harrogate and Leeds urban areas are close together; the superior acceleration of the stock over the Class 150 diesel multiple units currently used is intended to cut journey times. It was proposed, the line would be electrified with third rail similar to the Docklands Light Railway, as opposed to the London Underground or the Southern region network.
On 24 July 2012, unit 7007 was designated as the Olympic 2012 Train with the then Chief Operating Officer Howard Collins carrying the Olympic Torch from Wimbledon to Wimbledon Park. This is the only London Underground train to be an Olympic Torch train. - Wheelchair space
DM - Driving Motor car
T - Trailer (non-powered) car
UNDM - Uncoupling Non-Driving Motor car
De-icing equipment was fitted to trailers 17000 to 17048 (evens).
Withdrawals commenced on 19 January 2015 when the first full 6-car train, 7510+7058, was withdrawn from service at Ealing Common Depot and loaded onto trucks for Long Marston for the driving motors to be converted and the other cars to be either scrapped or stored for future use. All are scheduled to be replaced by S7 Stock by Spring 2017.
The mid-life refurbishment was the first to be carried out under the PPP, by Metronet, and was delayed until contract negotiations were completed. A prototype unit of three cars was prepared by London Underground's Train Modification Unit (TMU) at Acton Depot in 2001. This had some detail differences from the eventual refurbishment, and was later brought up to the standard of the rest of the stock. The refurbishment programme began in summer 2005 with the work undertaken by Bombardier Transportation's Derby facility. The programme was completed in 2008.
The refurbishment consisted of:applying London Underground livery with anti-vandal paint and window film
restyling the interiors in green and white
replacing maple flooring with rubber
adding end-of-car windows
replacing hanging straps (bobbles on springs) with grab bars
covering the door buttons
adding dot matrix indicators showing the station and destination on the inside and exterior front and sides
adding an audio passenger information system guided by GPS and odometer, voiced by Emma Clarke: announcements for each station name include connecting lines, and provide warnings to "mind the gap between the train and the platform"
adding a flip seat/disabled multi purpose area
fitting air conditioning to driver's cab
It is the first Underground stock to have electronic side-of-carriage information displays: some pre-war trains had slot-in or reversible destination or non-stopping plates.
In 2014, Vivarail purchased 150 Driving Motor cars and about 300 trailing vehicles of ex-District Line D78 stock for conversion to diesel-electric multiple units. It is proposed to run 75 units of two or three cars per unit. They will become known as class 230 under TOPS. A prototype was produced for testing and accreditation in August 2015, with introduction to service in 2016. They are to be tested in mainline service on the Coventry to Nuneaton Line.