Initial testing on Crossrail’s Elizabeth Line has now kicked off, with four trains an hour now running on the line.
It is the first phase in a series of major trials that must be completed before the much-delayed line opens in the first half of 2022.
The firm also said it had handed over the new station at Tottenham Court Road to Transport for London (TfL) so that it could be integrated into the existing network.
Over the coming months, Crossrail will slowly ramp up the number of trains operating in the newly built tunnels to test if the line can be operated as close as possible to the actual timetable.
By the time it opens, the line, which was due to open in 2018, will be four years overdue, with a total cost of £18.2bn – ahead of the budgeted £14.8bn.
Newly re-elected Mayor of London 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.”
Crossrail chief executive Mark Wild said that the start of trial running – which will take an estimated 9-12 months, was “hugely significant”.
“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.”