The firm renewing the London Underground has signed a lease to use a test track in part of Leicestershire.
The 13-mile (21km) track, near a former colliery at Asfordby, was part of the main rail line but closed in 1968.
Metronet Rail, which is having its Tube trains built at Bombardier in Derby, will spend £7m to turn at least 2.5-miles (4km) into a full test site.
Metronet will keep the track in a used condition to maximise the endurance testing of the new stock.
The work will see the 2.5 mile stretch of the line electrified and fitted with Underground-compatible rails.
Beeching cuts
The site at Asfordby was closed in 2005, following testing of the Virgin Pendolino tilting trains.
The track was closed during the Beeching cuts and then reopened by British Rail as a test track.
Metronet has leased the track to test the next generation of air-conditioned Underground trains, due to begin service on the Metropolitan line from 2009.
It will also be using workshops at the nearby former coal mine site as part of the project.
Metronet, which is renewing two-thirds of the Underground, is investing £3.1bn upgrading the Metropolitan, District, Circle and Hammersmith & City lines with new rolling stock, signalling, upgraded power and depots.
Mark Loader of Metronet said: "Old Dalby (test track) will enable us to really prove the reliability of these new trains - we'll be able to simulate six months to a year's service in only a month.
"That means a more reliable train for Tube travellers when they enter service."
