First Great Western is encouraging customers travelling between Swindon and Gloucester during April to check journey times and routes before travelling, as Network Rail carries out essential maintenance.
Customers can expect journeys to take between 30-55 minutes longer than usual, says the company.
But once completed, in August, the line upgrade between Swindon and Kemble via Gloucester and Stroud will allow for increased capacity as well as enabling fewer delays and a more reliable train service.
Network Rail is continuing its £45m project to upgrade the line, from Saturday, April 12, to Tuesday, April 15, road transport will replace trains between Swindon and Gloucester.
On Monday, April 14, and Tuesday, April 15, there will be a limited direct train service from Cheltenham Spa/Gloucester to London Paddington via Bristol Parkway.
At other times customers will also be able to use First Great Western and Cross Country services to Bristol Parkway and change there for direct services to London Paddington.
From Friday, April 18, to Monday, April 21, trains will operate between Cheltenham Spa/Gloucester and Swindon to an amended timetable. Customers for London Paddington should change at Swindon.
Mark Hopwood, First Great Western managing director, said: “This upgrade is vitally important to improve our customers’ travel experiences for the future.
“These works to the network infrastructure will pave the way for faster, more reliable services and makes the most of the Government’s planned investment in electrification and new trains – whoever has the privilege of running the franchise beyond 2015.”
While the impact of the work will be minimised, some rail services will be affected.
FGW tickets will be permitted for use by other train companies.
The planned work will include the reinstatement of the second line between Swindon and Kemble, upgrade to earthworks along the route to accommodate this new track and new signalling equipment.
This will be essential during the planned electrification of the Great Western main line when Bristol Parkway and Severn Tunnel are closed and south Wales trains are diverted along this route.
Network Rail will also need to close the line between Swindon and Gloucester on the week leading up to and over the August Bank Holiday weekend.
Passengers are advised to check travel plans online at www.firstgreatwestern.co.uk or www.nationalrail.co.uk, or to call FGW customer services on 03457 000125.