Crossrail trains built for London's new £15bn Elizabeth Line will not be coming as early as planned.
The first Crossrail trains were meant to start running between Liverpool Street and Shenfield by the end of this month.
A spokesperson has said good progress is being made though, and testing should be finished in the next few weeks, Essex Live reports.
Howard Smith, TfL's operations director for the Elizabeth Line, said: "The train is undergoing thorough testing, assurance and approvals before it enters passenger service shortly.
First line map unveiled as it is revealed trains should be operational from next month
"Good progress is being made and we anticipate testing being completed within the next few weeks.
"We continue to work closely with Bombardier, Network Rail and MTR Crossrail.
"About 11 Elizabeth Line trains are set to be rolled out from now until September along that part of the line, once the new train is in action."
Artist's impression of the trains that will run on the UK's largest rail project, Crossrail
Artist's impression of the trains that will run
The construction of a new platform 6 at Shenfield was completed at the beginning of May and additional capacity has been added to the railway at Shenfield to cater for the higher frequency service that will be provided once the Elizabeth Line extends from Essex and through the central tunnels in 2019.
This includes an extended platform 5, as well as three new sidings at Shenfield, each capable of accommodating the new trains.
The new trains will feature air-conditioning and three double-doors per carriage.
Crossrail will initially only run between Shenfield and Liverpool Street.
The stretch between Heathrow to Paddington is scheduled to start in May 2018, then Paddington to Abbey Wood in December 2018.
Paddington to Shenfield services will run by May 2019 followed by a full through service, including services to Reading in December 2019.