Crossrail is a step closer to opening after beginning safety trials.
The £19bn London rail link, also know as the Elizabeth line, has been plagued by delays and is expected to open four years behind schedule.
The service will run from Reading and Heathrow in the west, through 26 miles of new tunnels under London to Shenfield and Abbey Wood in the east.
When it opens, the Elizabeth line will cut the journey time from Heathrow to central London from 40 minutes to 20.
Londoners will also be able to cross the capital from Paddington to Liverpool street in just ten minutes.
Four test trains are now running along the length of the line per hour.
The number of trains will gradually increase before further activities such as timetable operation, timetable demonstrations and integration testing can be undertaken.
London mayor Sadiq Khan said: “Safely delivering the Elizabeth line as soon as possible is one of my top priorities, so I’m really pleased that trial running is now underway.
“The whole Crossrail team are doing all they can to get the railway open and ensure London and the wider south-east can enjoy its many benefits sooner rather than later.”
Each Crossrail train will be 200m long, almost twice the length of a London Underground train. Despite being bigger they will not be fitted with toilets.
However, free Wi-Fi and 4G will be available to passengers in air-conditioned carriages which will use up to 30 per cent less energy.
Mark Wild, Crossrail’s chief executive, said: “We have now started the trial running of trains on the Elizabeth line and this is an incredibly significant moment. It marks the moment when our focus shifts to commissioning of the new railway and it puts us firmly on the path to trial operations and ultimately the opening of the Elizabeth line.
“I want to thank everyone who has worked so hard over many years to get us to this point. There have been real challenges along the way but the start of trial running is an important milestone for the Elizabeth line and for London.”
The Elizabeth line has far exceeded its original budget of £14.8bn to more than £19bn.
Further delays were caused by the coronavirus pandemic which forced work on the project to stop.
Work resumed last year but only 2,000 workers were allowed onsite at any given time due to social distancing.
One of the main challenges facing the new line was the task of combining the three different stretches, which run on separate signalling systems.
Where does the Crossrail operate?
The Elizabeth Line links 41 stations across 62 miles of track.
The service will be overground in Berkshire, Buckinghamshire, Essex and parts of London with underground tunnels running beneath the city centre.
Passengers from as far as Reading and Shenfield will be able to reach Paddington, Bond Street, Liverpool Street and Canary Wharf without changing lines.
Existing stations: West
Hayes and Harlington
Acton Main Line
New stations: Central London
Tottenham Court Road
Existing stations: East