People using the railway network around the West of England are being warned of disruption as "vital" work to the Severn Tunnel's overhead power lines is due to start.
The tunnel, which links England and Wales, will be closed from Monday 9 June for 11 days, until 20 June, with reduced train services in place.
Trains between London and South Wales will stop at Gloucester instead of Bristol Parkway and replacement buses are planned to operate between Bristol Parkway and Newport, as well as Cardiff Central.
A limited train service will still run between London Paddington and Bristol Parkway.
Rail passengers travelling between Bristol and South Wales are being advised to change at Gloucester or Cheltenham Spa, where trains will still be running.
Network Rail programme director Ross Mahoney said: "All of this work is vital to ensure the continued safe and reliable running of the railway."
