Somerset has more than 120 “substandard” bridges, according to a study by the RAC Foundation.
Its study shows Somerset is among the worst counties in the UK for deteriorating bridges.
The study has found one in 24 bridges on Britain’s local roads are unable to carry the heaviest vehicles.
Local authorities identified 3,090 bridges across the UK as being “substandard” at the end of last year.
This means they are too weak to be used by 44-tonne lorries. Many are subject to weight restrictions, while others are under programmes of increased monitoring or even managed decline.
Devon has the most substandard bridges at 224, followed by Cheshire East (194), Essex (151), Somerset (128) and Suffolk (119).
Some are substandard because they were built to earlier design standards, while others have deteriorated over time.
The total of 3,090 substandard bridges is down from 3,211 a year earlier.
Between them, local authorities said they would ideally want to bring 2,506 of their substandard bridges back up to full carrying capacity.
But budget constraints mean they anticipate that only 387 will have the necessary work carried out on them within the next five years.
The analysis was based on data provided by 196 councils in response to freedom of information requests, and was carried out in partnership with Adept, a group representing local authority bosses responsible for transport and other sectors
Cllr David Renard, transport spokesperson for the Local Government Association, says: “Bridges, whether for rail, local highways or motorways, are a vital part of our transport infrastructure that connect communities and business.”
“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.”
A spokesman 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.”