New airconditioned trains will run on the London Overground line to Barking from 2018.
TfL has granted a £260m contract to transform the Gospel Oak route among others.
The new trains will have similar features to the fleet that currently serves other parts of the network including walk-through carriages and improved accessibility.
They will replace the existing trains which are more than 30 years old. TfL say the current condition of the fleet is in such a poor condition that it is causing delays.
TfL has also pledged to invest an additional £2m to modify trains to make them more reliable ahead of the arrival of the new fleet, which will be built in Derby.
Mayor of London Boris Johnson said: “This brand new fleet of trains will enable London Overground to carry a growing number of passagers more reliably and speedily than ever.”
Trains on TfL’s Liverpool Street to Enfield Town, Cheshunt and Chingford routes are also set be replaced.
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