Rail upgrade works affecting people travelling between south Wales, Bristol Parkway and London Paddington have begun.
Network Rail is doing work in the Chipping Sodbury and Alderton tunnels and building a new platform at Bristol Parkway.
The improvements will run from Saturday until 15 September.
They will allow new trains to run on the Great Western Rail mainline, including new intercity express trains.
For the duration of the works, those travelling between south Wales and London should note:
- High-speed services will call at Patchway, instead of Bristol Parkway, with reduced services during off-peak times.
- Replacement buses will run between Bristol Parkway and Patchway.
- From 19 August until 1 September, some peak time trains will still call at Bristol Parkway, as well as at weekends.
For those travelling to and from south Wales during the August Bank Holiday weekend from 26 August to 28 August:
- There will be no trains between Newport and Cardiff, with replacement buses running instead.
- Services will continue to run between Swansea and Cardiff - high-speed trains on the London Paddington to south Wales route will start and terminate at Newport.
During the weekends from 23-24 September until 18-19 November, there will be further improvement work affecting south Wales and Bristol Parkway services.
Passengers are advised to check their journeys.