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 project that became Crossrail has origins in the 1943 County of London Plan and 1944 Greater London Plan by Patrick Abercrombie.
Although the idea was seen as imaginative, only a brief estimate of cost was given: £300 million.
A feasibility study was recommended as a high priority so that the practicability and costs of the scheme could be determined.
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.
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.