RAC Foundation’s analysis of data for the 2017-18 financial year covers work that would be required on the almost 72,000 road bridges that are managed by councils.
Despite the financial pressures, annual expenditure by councils on maintaining bridges rose from an estimated US$465 million in 2016-17 to US$755 million in 2017-18.
The study is based on data provided by 200 out of a total of 207 councils across England, Scotland and Wales. Between them the 200 councils manage 71,652 bridges, of which 3,177 (4.4% of the total) are categorised as ‘substandard’. The substandard bridges are unable to carry the heaviest vehicles now seen on roads, including lorries of up to 44 tonnes.
The proportion of substandard bridges (4.4%) is in line with that reported in 2016-17 (4.6%, or 3,441 out of 74,005 bridges, based on data from 204 local authorities).
Between them, councils say they would ideally want to bring 2,026 (64%) of the 3,177 substandard bridges back up to full carrying capacity.
However, budget restrictions mean they anticipate that only 343 of these will have the necessary work carried out on them within the next five years.
The survey of local highways authorities was carried out by the RAC Foundation with the help of the National Bridges Group of the Association of Directors of Environment, Economics, Planning & Transportation (Adept).
The council with the highest number of substandard bridges is Devon, which has 2,712 bridges of which 244 of them are substandard, equating to 9%.
The council with the highest proportion of substandard bridges is Lewisham, where 18 of its 34 bridges are regarded as substandard.
The study said that no local authority manages structures directly technically comparable with the bridge that collapsed in Genoa in August 2018, but that 106 of the authorities do have post-tensioned (PT) bridges. Thes require specialist inspections but it was found that 199 of the total of 605 such bridges have not had a special PT inspection in the last 18 years.
The RAC Foundation also asked national roads authorities how their bridges were faring. Highways England and Transport Scotland each reported 1% of its bridges to be substandard. In England, there were 83 substandard bridges out of 11,067 while Scotland had 38 out of 2,641. The figure for Wales was 8%, with 96 out of 1,251 bridges deemed substandard.
Steve Gooding, director of the RAC Foundation, said: ““Establishing the condition of our highway bridges provides a litmus test for the condition of our road network more generally, and the condition is worrying. 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 sub-standard structures on some roads result in heavier vehicles having to make lengthy detours.”
Kevin Dentith, chair of the Adept National Bridges Group, said: “Bridge maintenance is about priority. In large rural counties, like my own authority, Devon, there will be structures that on paper fall short of current design standards, however they are never likely to be strengthened because they carry little more traffic than the odd car and tractor.
“However, there is a serious issue around so-called post-tensioned bridges. Whilst these are not directly comparable in technical terms to the bridge that collapsed in Genoa they do require intrusive examination, something many of them will never have had because of a lack of funding, expertise or both.”