The east–west scheme was for a line from Liverpool Street to Paddington/Marylebone with two connections at its western end linking the tunnel to the Great Western Main Line and the Metropolitan line on the Underground.
The City route was shown as a new connection across the City of London linking the Great Northern Route with London Bridge.
The other eastern branch runs underground from Whitechapel to Canary Wharf and Abbey Wood.
It takes over the Custom House to Woolwich via Connaught tunnel stretch of the former North London Line built by the Eastern Counties and Thames Junction Railway, and connects it with the North Kent Line via a tunnel under the Thames at North Woolwich.
Crossrail will be operated by MTR Corporation (Crossrail) Ltd as a London Rail concession of Transport for London, in a similar manner to London Overground.
It is expected to relieve pressure on existing east-west London Underground lines such as the Central and District lines, as well as the Jubilee line extension and the Heathrow branch of the Piccadilly line.
One of the two eastern sections runs underground from Whitechapel to Stratford, then on the surface on the existing main line.
The service will replace the "Shenfield metro", with key stops at Ilford, Romford (for interchange with London Overground services to Upminster), Gidea Park (where some peak hour trains will start or terminate), and Shenfield.
Upgrades are being made to stations at Maidenhead, Taplow, Burnham, Slough, Langley, Iver, West Drayton, Hayes & Harlington, Southall, Hanwell, West Ealing, Ealing Broadway and Acton Main Line.Part of the eastern section, between Liverpool Street and Shenfield in Essex, was transferred to a precursor service called Tf L Rail in 2015; this section will be connected to the core route through central London to Paddington from May 2019.The western section, from Paddington to Heathrow Airport and Reading in Berkshire, is due to open in December 2019, completing the new east–west route across London and providing a new high-frequency commuter and suburban passenger service.The need for extra capacity along this corridor is such that the former head of Tf L, Sir Peter Hendy, predicted that the Crossrail lines will be "immediately full" as soon as they open.The concept of large-diameter tunnels crossing central London to connect Paddington in the west and Liverpool Street in the east was first proposed by railwayman George Dow in The Star newspaper in June 1941.