Disruptive platform works at Broxbourne railway station are complete.
According to Greater Anglia, new 10-car commuter trains are now being tested at Broxbourne, Ware and Hertford East.
The work has caused disruption to trains between London, Hertford, Stansted Airport and Cambridge throughout 2022 - including an eight-day works programme in April and five days of cancellation to Stansted Express trains in August.
A Greater Anglia spokesperson said: "Longer trains will soon be able to stop at stations along our Hertford East line after major work to make platforms longer at Hertford East, Ware and Broxbourne was finished over the bank holiday weekend.
"We're now able to carry out test runs of our new 10-carriage commuter trains along the line to make sure they can safely enter passenger service as soon as tests are complete.
"A big thank you to everyone along the Hertford East line for your patience while this work was carried out."
In the future, Broxbourne is set to be included in a potential Crossrail 2 line between Surrey, south-west London and Hertfordshire, through Victoria, Tottenham Court Road and Dalston.
Sir Alan Hazlehurst, former MP for Saffron Walden, chaired the West Anglia Task Force in 2016.
He said at the time: "The need for investment in the West Anglia Main Line is overwhelmingly clear.
"With the right investment, spectacular growth from inner London through the Upper Lee Valley, Hertfordshire, Harlow, Stansted Airport and all the way to the outstanding University of Cambridge could be unleashed."
He said the region does "not have the luxury" of an easy alternative to creating more capacity on the line through Broxbourne.
In recent months, Prime Minister Boris Johnson has backed the project.
On May 17 this year, when the Elizabeth line opened, he said: "The real thing for us now is to think about Crossrail 2, the old Chelsea-Hackney line.
"That is going to be transformative again.
"All the problems of commuters coming into Waterloo getting up to north London, you can fix that with another Crossrail."
In a funding deal agreed between the government's Department for Transport and Transport for London, none of the £3.6 billion settlement - due to last until March 2024 - is guaranteed for Crossrail 2 and Broxbourne.
The funding deal report reads: "To complete the prioritisation of any agreed updating of the safeguarding regime for Crossrail 2, DfT and TfL will enter into an appropriate agreement as soon as reasonably possible whereby they agree to share equally the costs of any statutory blight claims arising from the updated safeguarding regulations for the scheme."
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