Wind tunnel modelling to boost safety on M4 Prince of Wales bridge

Replacing a steel barriers with concrete is normally straightforward. Not on the 5,128 metre Prince of Wales bridge carrying the M4 across the River Severn.

High winds can make the suspended section of the bridge shake. Making sure any changes to the structure won't increase this effect is a design challenge in itself.

We undertook an innovative feasibility study to make sure a new barrier design would be aerodynamically stable in windy conditions.

Working with a wind tunnel allowed us to model the effects of wind on our barrier design in a variety of different scenarios. We were assisted by specialist consultant RWDI, whose wealth of experience includes work on the Golden Gate Bridge

Testing allowed us design a concrete barrier that will have virtually no effect on the bridge.

We aim to start building the barrier in 2025-26. It will be a significant improvement to the existing metal barrier, reducing the risk of vehicles crossing into the opposite carriageway. This makes the bridge safer and reduces the risk of congestion if incidents do occurr.

Concrete will also last twice as long as the original metal barrier, needing less maintenance.

Matthew Jones, Asset Needs and Programme Development Manager for the Specialist Bridges Group, said:

“We are constantly exploring new innovative ways to design, build and maintain our roads and are committed to making them safer. We believe that embracing innovation and working closely with engineering specialists is the path to more efficient and safer projects.

“By undertaking modelling, trials and tests like these, we can ensure we’re making the right changes to see significant long-term benefits and improve the experience of our roads for motorists.

“Upgrading these barriers will improve journeys and significantly reduce the risk of vehicles crossing over from one carriageway to another, improving safety and reducing the duration of incident-related congestion.”