How and why the Badminton Road M4 bridge will be replaced

NATIONAL Highways has explained why the Badminton Road bridge over the M4 needs to be replaced, how it will be done and how long it will take.

The bridge was opened in 1966, and was designed to last 120 years. 

But in less than half of that time, the government agency has decided that it needs to be demolished and replaced.

The bridge, which carries the A432 between the Avon Ring Road and Yate, was being used by a around 16,000 vehicles a day when it closed.

The M4 underneath it carries around 87,000 vehicles a day.

Before work can start on demolition, services including electricity cables, water mains, BT fibre optic cables and gas mains all have to be moved and buried in trenches under the M4.

The Highways Authority say the timescale will be:

*January 2024: ecology work and habitats

*February 2024: ground investigations and boring.

*March to May 2024 : moving and re-routing pipes and cables

*Summer/Autumn 2024: demolition

*Late 2024: New build starts

*Early 2026: New bridge opens.

National Highways route manager Sean Walsh said the demolition will happen in a 60-hour window when the M4 will be closed, so they can remove the central span of the structure. 

At other times there will be ongoing lane closures on the M4 and overnight closures for the rest of the work.

Mr Walsh said: “The build is a 12 to 18-month project – much shorter than normal, as we realise the importance of accelerating this build.”

‘Very rare’ structural cracks go right through bridge

Cracked concrete on the underside of the bridge. Picture: National Highways

He said National Highways is responsible for 2,200 structures in the South West – 164 are similar ‘post-tension’ structures like the Badminton Road bridge, which is the only one with major issues.

Mr Walsh added: “In 16 years in this job, this is the only bridge I’ve seen that has this magnitude of work needed.

“It’s very rare we have to demolish and rebuild a whole bridge – this is the only one in the region.”

He said the 120-year design life was predicted when traffic numbers, lorry sizes and other factors were all very different to today.

National Highways’ Sean Walsh talks to reporters about the M4 bridge’s problems

Engineering team manager Terry Robinson said all road bridges undergo ongoing maintenance during their lifetime and, behind the scenes, teams were always working to do this. 

But the issues found by inspectors in the summer were exceptional.

He said: “The examination showed structural cracks going right through the bridge.

“We’ve been working solidly since July to examine the bridge and find out how bad the problems are, and what the possible solutions are. 

“The bridge is not unsafe and is not at risk of collapse, but it’s unable to carry heavy traffic.

“Traffic will cause the carriageway to move and because of the cracks, that could result in a piece of concrete landing on the M4 below, so that is why it has to be closed now.

“We have assessed it as perfectly safe for pedestrians and cyclists.

“We’re speeding things as quickly as we can to get the bridge back open as soon as possible.

“The whole program has been condensed, as we know it’s important to local people.”