Tens of millions of pounds must be spent to restore the backlog of substandard bridges in Buckinghamshire to a good condition, new figures show.

The RAC Foundation said the threat of more severe weather due to climate change could lead to dangerous collapses on Great Britain's highways and has urged councils to address unsuitable bridges.

Out of 372 bridges in the area, Buckinghamshire council identified two which were unable to carry the heaviest vehicles regularly using highways – including lorries up to 44 tonnes – in 2021, figures from the RAC Foundation show.

The council estimates it would cost £23.1 million to restore them to a good condition. Nationally, local councils estimate they need to spend £4.2 billion on bridge restoration.

The national bridges group of the Association of Directors of Environment, Economy, Planning and Transport has urged the Department for Transport to invest in repairing bridges or face the risk of seeing more collapses than identified in the RAC Foundation figures.

Councils reported 17 complete bridge collapses in 2021 – 12 in Dorset and five in Denbighshire. A further 37 partially collapsed.

A Department for Transport spokesperson said: "We are providing more than £5 billion of investment over 2020 to 2025 for highways maintenance to local highways authorities across England, including for the repair and maintenance of bridges.

"It is up to councils to decide how they use highways maintenance funding, based on their own needs and priorities."

Across Great Britain, local authorities assessed 3,211 substandard bridges at the end of last year – up from 3,105 the year before and the highest number since 2017.

It means 4.5% of bridges across Great Britain are deemed unsuitable. This could be because they were built to earlier design standards, while others have deteriorated through age and use.

Many are subject to weight restrictions, while others are under programmes of increased monitoring or even managed decline.

The RAC Foundation analysis is based on data provided by 196 councils in response to freedom of information requests.

Of the local authorities with more than 100 bridges, Oxfordshire has the greatest proportion deemed substandard (28%), while Devon has the highest total number of substandard bridges – 229 out of 2,714 (8%).

Steve Gooding, director of the RAC Foundation, said: "Even the failure of the shortest of these structures could mean a five-foot long gap in the carriageway, and even on relatively minor roads that can still be a headache, causing disruption and possibly a long diversion.”

The figures also show Buckinghamshire council does not intend to return any of its bridges to full carrying capacity in the next five years.

The council said one bridge would ideally be brought up to scratch over this period if it did not face budget limitations.

Councils across Great Britain said they would fix 2,374 (74%) bridges without budget restrictions, but just 379 (12%) are anticipated to be restored within the next half a decade.