[5] However the journey to central London on the Piccadilly line takes around 40 to 50 minutes, the same time as a black taxi.

[14] In August 1993, British Rail and BAA signed the contract to build the line, with an opening date of December 1997.

[9] The principal works were two 6.8 km (4.2 miles) single-bore tunnels (including eight escape shafts) and underground stations at Heathrow Central and Terminal 4.

[8] A flying junction known as the Stockley Flyover was constructed to connect the tunnel to the GWML fast lines.

As part of the construction of the project, steps were taken to reduce the environmental and visual impact of the railway, including disguising ventilation shafts as barns.

[27] Railtrack proposed a stopping service from Heathrow to St Pancras, by using London Underground tracks.

[27] This was part of Railtrack's bid to win the public-private partnership (PPP) contract to upgrade and maintain the sub-surface lines of the Underground.

[34] During August 2018, Great Western Railway (GWR) took over the operation of Heathrow Express as part of a new management contract.

[39] This continued until May 2018, when Heathrow Connect was absorbed into TfL Rail ahead of the new Crossrail project.

[40] In May 2022, TfL Rail services were rebranded as the Elizabeth line, with through trains running through central London from November 2022.

[41] Trains depart Paddington every 15 minutes from 05:10 (06:10 on Sunday) until 23:25,[42] and there is a similar quarter-hourly service in the return direction.

[46] The service runs along Network Rail's Great Western Main Line from Paddington to Airport Junction.

[38] The units transferred from Great Western Railway who are also responsible for their maintenance and operation within Heathrow Express.

[36] The units underwent modifications prior to their introduction on Heathrow Express which included the fitting of USB power sockets, extra luggage space, work tables, on-board Wi-Fi and HD TVs.