Weeks of disruption for passengers on one of UK's busiest rail lines

People travelling on one of the UK's busiest rail lines face weeks of disruption as engineers replace overhead power lines that corrode quicker than any other part of the network.

The Severn Tunnel, which connects south Wales with London and Bristol, will shut for 16 days from Saturday as workers fit a pioneering copper power line inside what was once the world's oldest underwater rail tunnels.

Water that would fill 20 Olympic pools is pumped from the 140-year-old tunnel every day as saltwater from the River Severn constantly drips through its thick walls.

Direct GWR services between London and south Wales will take longer on a revised timetable while buses replace some train services.

Passengers have been "strongly advised" to check their train times and allow extra travel time between south Wales and the south of England during the closure, between 23 May and 8 June.

Network Rail will also carry out track upgrade work around Bristol ready for the MetroWest project with a new station set to open on the former Filton airfield site later this year.

Rail bosses hope the £23m electrification upgrade project can ultimately improve train reliability and reduce the number of power failures and maintenance closures inside the Severn Tunnel .

About 200 trains normally travel through the 4.5 mile (7.2km) structure every day.

It has only once been shut for longer since it opened in 1886 - that was when electric wires were installed 10 years ago as part of the £2.8bn south Wales main line electrification project.

Network Rail has called the Victorian tunnel one of the most hostile environments on the UK rail network, where moisture, dripping saltwater and diesel soot accelerate wear on equipment.

Three years after the electric wires were installed in 2019, electricity still wasn't powering trains in the tunnel because of issues with the overhead lines.

The first electric powered train passed through in June 2020 but the tunnel's overhead power system has since suffered corrosion and electrical wear, meaning more frequent maintenance.

Engineers have spent years designing a bespoke world-first fixed copper contact wire power supply for trains in the tunnel to replace the standard overhead equipment.

Network Rail said the new system "eradicates the failure mechanisms of the past by providing complete separation of bimetallic elements and using a copper contact wire which improves current collection" from overhead wires by trains.

"If you look at the track, you'd expect it to last about 25 years outside the tunnel but within the tunnel because of the corrosive environment, it's around 10 years," said Ben Perkins of Network Rail.

"You can apply that logic to the overhead systems, it's a much shorter lifespan inside the tunnel hence the requirement for looking at a more resilient, higher-performing design," Perkins added.

"The Severn Tunnel is the heartbeat of this main line, it's important in connecting communities on each side of the Severn so it's very important that it's operational and reliable."

Network Rail said it had chosen the quietest time possible to shut the tunnel, avoiding major sports events in south Wales and big summer music concerts in Cardiff.

And rather than shutting the structure a number of times over weekends to complete the work, engineers said shutting it once but for a longer period of time was more cost-effective and would save time in the long run.

"We know that bus replacement services are a significant ask of passengers and we're genuinely grateful for their patience while this vital work is completed," said Marcus Deegan of GWR.

While Network Rail has closed the track leading up to the tunnel, it will also carry out track and infrastructure upgrades and drainage works in the Bristol and Patchway areas.

The work will allow passenger services to start running on the old Henbury line for the first time since 1964 and will connect the new Bristol Brabazon station - previously known as North Filton - to the rest of Bristol.

That station on the former Filton airfield site will serve the new Aviva Arena - which is expected to open in 2028 - and a nearby conference centre, 15-acre park, schools, leisure facilities and 6,500 homes.

"We're renewing track that will bring passenger services back to the Henbury and Portishead lines for the first time in over 60 years, supporting local communities and economic growth," said Nia Watkins of Network Rail.

Rail operators have warned passengers to check before they travel and leave plenty of time as all services between south Wales and the south of England will be affected until 9 June.

Some south Wales to London trains will continue to operate directly but will take about 45 minutes longer and go via Gloucester - except on Sunday 24 May.

Replacement bus services will run between Newport and Bristol Parkway while a reduced GWR service will run between London Paddington and Bristol Parkway.

For more detailed information, please check the GWR website.

CrossCountry and Transport for Wales train services between Cheltenham Spa or Gloucester and south Wales will be unaffected.