The maintenance backlog for council-owned road bridges in Britain has increased by a third in 12 months, new figures show.
An estimated £6.7 billion is needed to ensure all the structures are up to scratch, according to analysis of 2017/18 data by motoring research charity the RAC Foundation.
This is up from £5 billion a year earlier.
Some 3,177 bridges in the worst condition have been categorised as “substandard”, meaning they are unable to carry the heaviest vehicles.
Many of these structures are subject to weight restrictions while others are under programmes of increased monitoring or even managed decline.
Some are substandard because they were built to earlier design standards, while others have deteriorated through age and use.
Between them, local authorities say they would ideally want to bring 2,026 of these bridges back to full carrying capacity.
But budget constraints mean they anticipate that only 343 of these will have the necessary work carried out on them within the next five years.
The analysis is based on figures provided by 200 out of the 207 local highway authorities across Britain, which manage 71,652 bridges.
It was carried out in partnership with Adept, a group representing local authority bosses responsible for transport and other sectors.
RAC Foundation director Steve Gooding said establishing the condition of highway bridges is a “litmus test for the condition of our road network” and described the findings as “worrying”.
He went on: “While we should draw some comfort from the good knowledge highway authorities have about the strength and structural integrity of their bridges, the fact is that many thousands are subject to enhanced monitoring, speed and weight restrictions, and the cost of bringing them up to scratch is continuing to mount.
“Ancient bridges on rural back roads might not be the highest priority for repair, but the risk we run is that substandard structures on some roads result in heavier vehicles having to make lengthy detours.”
The research found that no councils manage structures which are “directly technically comparable” to the bridge that collapsed in Genoa, Italy in August 2018, killing 43 people.
But some local authorities do have a number of so-called post-tensioned (PT) bridges with hidden cables, as was the case with the Morandi bridge.
These PT bridges require intrusive inspections that can cost £100,000.
Almost a third (33%) of the 605 PT bridges managed by Britain’s councils have not had this test carried out in the last 18 years, despite requiring it.
Martin Tett, transport spokesman at the Local Government Association, representing 370 councils in England and Wales, claimed the study “underlines the chronic need for more investment in existing local roads”.
He said: “While the extra one-off £420 million funding announced in the Budget will help, only long-term, consistent and fairer government investment in local road maintenance can allow councils to embark on the widespread improvement of our roads and bridges that is desperately needed.”
Last month a weight limit was introduced on a Ministry of Defence-owned road bridge in Weston-super-Mare, Somerset, as traffic vibrations were causing debris to fall onto a railway line below.
Repair work on Wool Bridge in Dorset – which features in Thomas Hardy’s novel Tess of the D’Urbervilles – was completed in November after parts of it collapsed into a river in January 2018.