and location of door controls. All underground trains are required to comply with The Rail Vehicle Accessibility (Non Interoperable Rail System) Regulations 2010 (RVAR 2010) by 2020. Stock on sub-surface lines is identified by a letter (such as S Stock, used on all subsurface lines), while tube stock is identified by the year in which it was designed (such as 1996 Stock, used on the Jubilee line). Future development plans New Tube for London (NTfL) The Deep tube programme (DTP) originally covered the replacement of the trains and signalling on the Bakerloo and Piccadilly lines. It had been expanded to cover rolling stock requirements arising from the planned extension of the Northern line to Battersea, the eventual replacement of Central line trains and proposed increased service frequency on the Northern and Jubilee lines. The EVO tube concept design, a lighter articulated train with walk through cars, was introduced early in 2011. In early 2014 the Bakerloo, Piccadilly, Central and Waterloo & City line rolling stock replacement project was renamed New Tube for London (NTfL) and moved from its feasibility stage to the design and specification stage. The proposal introduces fully automated trains and signalling to replace 1972 Stock, 1973 Stock & 1992 Stock and increase capacity on the Piccadilly, Central, Waterloo & City and Bakerloo lines between 2025 and 2033. The fully automated trains may not have drivers. The ASLEF and RMT trade unions that represent the drivers strongly oppose this, saying that it would be unsafe. Internal investigations from TfL revealed that the upgrades required to operate driverless trains were economically unviable. History Steam locomotives District Railway The first services were run by the Metropolitan Railway. In 1871 the District Railway began running its own services with locomotives that were identical to the Metropolitan Railway A Class already in use. Twenty were supplied initially, and by 1905 the District had 54 locomotives. After the railway had been electrified by 1907 all but six of the steam locomotives had been sold. In 1925 two locomotives were retained for departmental use. Metropolitan Railway Concern about smoke and steam in the tunnels led to trials before the line opened with an experimental "hot brick" locomotive nicknamed Fowler's Ghost. This was unsuccessful and the first public trains were hauled by broad gauge GWR Metropolitan Class condensing 2-4-0 tank engines designed by Daniel Gooch. These were followed by standard gauge Great Northern Railway locomotives