Engineers have upgraded the overhead lines on the railway running through the Severn Tunnel between South Gloucestershire in England and Monmouthshire in Wales, using a pioneering engineering technique.

With one of the most challenging environments on the UK rail network, the line through the Severn Tunnel suffers from a combination of saltwater and moisture, which accelerates wear on overhead line equipment through bi-metallic corrosion. The solution that Network Rail developed to overcome this problem uses modified bridge arms and a continuous copper contact wire, which creates a more resilient and reliable railway, while reducing maintenance.

Last year, Network Rail and its contractor ARQ (AmcoGiffen, REL and QTS) trialled the solution on the westbound line, and have now completed installing the system on the eastbound line. The work marks the successful completion of a world-first engineering solution inside the 4.35-mile tunnel beneath the Severn Estuary, where a unique combination of saltwater, moisture and a highly corrosive atmosphere creates one of the most challenging environments on the UK rail network.

Around 250 engineers worked around the clock from Saturday, 23rd May, to Tuesday, 9th June, when the tunnel reopened to normal services. In total, 838 overhead line support arms were replaced, and 14 km of new wiring over 7 km of single copper contact wire supported by the modified bridge arms were installed.

Two years ago, all of the track on the westbound line through the tunnel was renewed.

“The Severn Tunnel is one of the most challenging environments anywhere on the UK rail network, so completing this upgrade is a significant achievement for everyone involved.Following a successful trial last year, we’ve now delivered a world-first engineering solution at scale, designed specifically to withstand the uniquely harsh conditions inside the tunnel. This is the result of years of innovation, planning and collaboration between Network Rail and our industry partners to solve a long-standing challenge on a vital rail link between South Wales and England.”

“Investing in innovative solutions like this helps us build a more resilient and reliable railway for the future. By reducing the impact of corrosion and the need for maintenance, this new system will help keep passengers and freight moving on a route that plays a crucial role in connecting communities, supporting businesses and driving economic growth on both sides of the border. I’m incredibly proud of the hundreds of colleagues and contractors who worked around the clock to deliver this complex upgrade safely and successfully. I’d also like to thank passengers, freight operators and local communities for their patience and understanding while we carried out this essential work.”

Nick Millington, Route Director at Network Rail Wales and Borders