Chelsea–Hackney line

The Chelsea–Hackney line (also referred to as the Chelney line, Kings line and Crossrail 2) is a safeguarded route for an underground railway running from south-west London (UK) to north-east London. The route in its modern form was first drawn up in the 1970s and although it is the highest profile project not yet under construction, it will not proceed before the competition of Crossrail 1 in 2018. During the early 2000s the plan was developed by Cross London Rail Links Ltd., the developers of Crossrail, and the line is therefore sometimes known as Crossrail 2 and expected to be a large gauge tunnel.

Current plans
The current plans, safeguarded in 2008, include linking the District line's Wimbledon branch with the Central line's Epping branch via a route from Parson's Green to Leytonstone via Chelsea, Sloane Square, Victoria, Piccadilly Circus, Tottenham Court Road, King's Cross St. Pancras, Angel, Essex Road, Dalston Junction, Hackney Central and Homerton. The safeguarding also includes a spur from Victoria across the Thames to Battersea Park for stabling and access to a tunnelling site. The tunnel size that has been safeguarded is national rail standard (same as Crossrail 1). However the final decision as to the loading gauge has not yet been decided.

Euston / High Speed 2
The line is considered the fourth major rail project in the capital after the Thameslink Programme (est. completion 2018), East London line extensions (2012) and Crossrail 1 (2018). National Rail's projections of overcrowding led them to call for more new lines such as Chelsea-Hackney but plans have gained more importance with the emergence of Euston as the London terminus of the planned High Speed 2 rail line. High Speed 2 would bring an estimated 20,000 passengers onto the congested Northern and Victoria lines at Euston so if HS2 is approved Transport for London (TfL) plan to change the safeguarded route for Chelsea-Hackney to alter the alignment of the tunnels between Tottenham Court Road and Kings Cross St. Pancras so that a new station can be built at Euston. By bringing in the Euston station to relieve a rebuilt Euston High Speed interchange, the Chelsea–Hackney line has a considerably improved business case. Indeed, due to the expected numbers flooding onto the tube network at Euston, it would become a necessity. While it is not affordable in the early 2010s, it would be cheaper than Crossrail 1 due to fewer central London stations and it was reported in February 2011 that the Mayor of London would be talking a lot more about building the new line.

Early plans
A west/north-east tube line was originally planned as early as 1901 and a bill was put before parliament in 1904. However political manoeuvring by rival tube magnate Charles Yerkes killed off the proposal.

1970s
The plan was revived in 1970 by London Transport's London Rail Study as the next project after the completion of the Victoria line and the Fleet line (renamed as the Jubilee line). Designed to relieve pressure on the District, Central and Victoria lines, and to link two areas without tube services, the route would have taken over the branch of the District as far as, then followed a new underground alignment to , where it would then take over one of the branches of the Central Line. For financial reasons the line was not built, but over the years the idea, or variations of it have emerged. The proposal as of the 1974 London Rail Study was: Commencing at (takeover or share the District line branch) Continuing to (takeover or share the Central line branch)
 * Millbank
 * (takeover the former Piccadilly line shuttle to Holborn)
 * Shoreditch Church
 * Dalston Junction
 * Hackney Downs / Hackney Central
 * Hackney Wick
 * (takeover the former Piccadilly line shuttle to Holborn)
 * Shoreditch Church
 * Dalston Junction
 * Hackney Downs / Hackney Central
 * Hackney Wick
 * Shoreditch Church
 * Dalston Junction
 * Hackney Downs / Hackney Central
 * Hackney Wick

1980s
Following the Central London Rail Study of 1989, a route through central London was safeguarded. In the existing safeguarding of the route, the line would start from through to :- from there taking the Central Line through to. As the route would serve both King's Cross and Kings Road it was suggested that the line could be named Kings line. It was decided however that the Jubilee line Extension should take priority and the project was postponed.
 * Essex Road
 * Dalston Junction
 * Hackney Central
 * Homerton
 * Essex Road
 * Dalston Junction
 * Hackney Central
 * Homerton
 * Essex Road
 * Dalston Junction
 * Hackney Central
 * Homerton

1990s
In 1995, an alternative plan, the Express Metro was put forward that would utilise more existing track, have fewer stations and be built to National Rail standards. It would take one of three routes from on the District Line to  station; either,  and  or (King's Road) as in the original safeguarded plan; or to Wandsworth Town and Clapham Junction and then either via Chelsea Harbour and King's Road or via Battersea. From Victoria it would then call at and then split into two branches, one to and then on to  taking over the Central Line, the other taking over the North London Line to Woolwich, since used by the Docklands Light Railway. The 1991 safeguarding also included a spur south of Victoria across the river to Battersea Park, but this was only for stabling of trains and to access a riverside tunnelling site.
 * Dalston Kingsland
 * Hackney Central
 * Dalston Kingsland
 * Hackney Central
 * Hackney Central

2000s
The London East West Study in 2000 considered Crossrail, the Chelsea–Hackney line and a combination of the two, going from to  and then on to. The Study supposes mainline gauge, and therefore would omit a station at. Its version of the Chelsea-Hackney Regional Metro splits in the north, with one branch going via Dalston and taking over the branch of Central line, and the other heading to, then using the disused alignment of the Northern Heights plan, taking over the  branch of the Northern Line. The Express Metro option instead would run on the East Coast Main Line. In 2007 the east-west Crossrail was given the go-ahead over the Chelsea–Hackney despite some commentators favouring the later (putting the implementation of the line back behind Crossrail's completion date: 2018) and the Chelsea-Hackney plans were taken over by Crossrail and the project was labeled Crossrail 2. In 2007, the 1991 route was updated – Sloane Square was dropped from the plan and it was decided to take over the Central line's Epping branch from Leytonstone and re-safeguarded. Due to objections from residents of Sloane Square, it was reintroduced the following year. Southwest Trains' Wimbledon depot was also safeguarded as a depot for the new line. The safeguarding was enlarged from a tube gauge line to a national rail loading gauge as it became clear that larger and longer trains would be needed. Of the three routes proposed for south-west London the Royal Borough of Kensington and Chelsea initially favoured one going south via Imperial Wharf to Clapham Junction, but now supports the more traditional take over of the District line's Wimbledon branch. Under these present plans, only one entirely new station would be constructed - at Chelsea.

Criticism and other proposals
A link to Clapham Junction from via Imperial Wharf is also being examined although it is not part of the protected route. This would end that station's isolation from the London Underground network. Clapham Junction was shown as an interchange with Crossrail 2 on an earlier TfL East London Line routemap. There is also the possibility of another station outside what is on the official safeguarding. Hackney Council plans show a station around the Temple Mills area (almost in Newham) which if it becomes part of the official plans would be in the north part of the Olympic Park. The plan, dated before 2005 awarding of the Olympics, showed the station to be roughly where the Northern Transport Interchange for the Olympic Park now is. No interchange station with the Jubilee line has been proposed as yet, despite the two routes crossing between and  on the safeguarded route and between  and  on the Jubilee line. This makes the Jubilee line the only London Underground line (except for the Waterloo and City line) with no proposed interchange with the new route.