Millions of pounds are needed to restore substandard bridges in Gwynedd, new figures show.

The RAC Foundation said there is only so long councils can continue “patch things up before bigger cracks literally start to appear” in road infrastructure. Their figures show that of the 631 bridges in Gwynedd, 18 were substandard last year, meaning they are too weak to carry 40-tonne vehicles, or there is a weight restriction for environmental reasons such as a narrow bridge or narrow approach roads.

The council estimate it will cost £40 million to bring the bridges back to good condition. Across the UK, councils said 3,090 bridges were substandard – accounting for 4.3 per cent of 71,925 bridges. It was down slightly from 3,211 reported the year before (4.5 per cent). The estimated one-time cost to clear the maintenance backlog on bridges across the nations was £5.9 billion.

Steve Gooding, director of the RAC Foundation, said: “The numbers illustrate how important it is for significant sums of money to be spent tackling at least the higher priority work.

“Whether it is potholes or bridges there is only so long that councils can continue to patch things up before bigger cracks literally start to appear in the road network.”

No collapsed bridges were reported across Great Britain last year, however there were 14 partial collapses.

David Renard, transport spokesperson for the Local Government Association, said: “Not all bridges are the responsibility of councils, but for those that are, they are doing their best to ensure they are well maintained and withstand extreme weather, the like of which communities have been experiencing for much of the last few months.

“However, this is becoming increasingly challenging in the face of a backlog of nearly £12 billion to bring our local roads up to scratch.”

Gwynedd Council said it would ideally restore all 18 bridges to full capacity, but only foresees one returning to good condition in the next five years.

A spokesperson for the Department for Transport said: “The government is providing more than £5 billion of investment over this Parliament to local authorities across England to support the maintenance of their local highway infrastructure, including the repair of bridges and the resurfacing of roads up and down the country.”