Four and a half billion pounds will be spent on 600 carriages for the routes from Paddington to Reading, Newbury, Swindon, Oxford and Banbury.
It should lead to major improvements in the Thames Valley.
But a row has broken out about the contract being awarded to a Japenese company.
Click below for the full story
More top news
Wednesday afternoon's weather for the east of the region
Wednesday afternoon's weather for the west of the region
Wednesday's weather for the east of the region