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.
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Councils are being asked to waive road closure charges so people can hold street parties for Prince Harry and Meghan Markle's wedding.
James Wright has the weather for the west of the region
James Wright has the weather for the east of the region