More than 2,000 road bridges on mainland Britain are not fully usable, according to research.
Data collected and analysed by motoring charity the RAC Foundation shows that 2,375 structures over 1.5m in span are not fit to carry the heaviest vehicles.
The organisation said many of these bridges had weight restrictions, while others were subject to increased monitoring or managed decline. All 2,375 are unable to cope with 44t lorries, meaning a huge number of routes were off-limits to certain vehicles.
RAC Foundation said some of the bridges were built to old design standards, while others had deteriorated through age and use.
The body estimated that it would cost £328M to bring them all up to perfect condition.
An RAC Foundation spokesman said the government could consider creating a ringfenced fund for the job.
The RAC Foundation and the Association of Directors of Environment, Economics, Planning and Transportation (Adept) called for protection of funding for highways maintenance in this month’s government Spending Review.
“Highways maintenance doesn’t start and end with filling in potholes - though that in itself is a big enough job,” said RAC Foundation director Steve Gooding. “Another key responsibility for councils is to keep their highways bridges up to scratch.
“Four years ago the Hammersmith Flyover in London had to be shut to traffic because it had deteriorated badly. It caused major congestion and was a graphic illustration of what could happen if our national infrastructure is not adequately maintained.
“Councils are doing their utmost to keep their structures inspected but where they find fault, the price of repair can bust the hard-pressed maintenance budget. We hope the chancellor has this in mind as he completes his spending review calculations this month.”
Adept Bridges Group chair Liz Kirkham said: “The Adept Bridges Group works hard to support local authority bridge managers in maintaining these vital links in the highways network, and is concerned that further reductions in available funding will only make their job more difficult.”
A Local Government Association spokesperson said councils took road safety extremely seriously, and were doing everything they could to keep traffic moving.
“However, they are caught between a rock and a hard place,” he said.
“On the one hand they are faced with a predicted 55% increase in traffic on local roads within a quarter of a century, according to the government’s own statistics. On the other hand, their core funding has been reduced by 40%.
“What is needed is realistic funding to maintain existing bridges and build new infrastructure, and clarity from the government about when and how they will get the money.”
A Department for Transport spokesperson said a well-maintained local road network was essential for all road users.
“That is why we are providing nearly £1bn to councils in England to help repair local roads, including bridges and other structures, this financial year,” they said. “This funding allows councils to plan ahead and repair their highways properly.
“Councils run their own maintenance programmes so they can focus on the roads and infrastructure that need urgent attention, and work on improving journeys for local people.”
Civil Engineering Contractors Association chief executive Alasdair Reisner this month warned that cutting departmental revenue budgets could lead to lower spending on vital roads maintenance work. His comments came after chancellor George Osborne revealed that he was slashing the “day-to-day” spending power of four departments - including the Department for Transport (DfT) - by an average of 30% for the next four years (News last week).