Rail passengers face 10 days of disruption as engineers close tracks to install new points.
From Saturday, August 21, two of the four tracks on the Great Western mainline between Reading and London Paddington will be closed.
The other two tracks will also be closed on Saturday August 28, as 100 engineers work around the clock to complete the work.
All four lines will re-open to passenger services on Tuesday, August 31.
The £8 million engineering project is designed to improve the punctuality and reliability of trains in the south west.
Linda Hill, the head of customer services at First Great Western, said: "This is a crucial project and we have drawn up the best possible timetable for our customers while allowing Network Rail to complete the work."
Customers can find out how the work will affect services by contacting National Rail Enquiries on 08457 484950 or by consulting www.nationalrail.co.uk before travelling.
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