The sub-standard bridges were identified in Brent and Barnet, according to the RAC Foundation.
Barnet Council was just one of ten local authorities that reported a partial bridge collapse in the financial year 2021-22.
Brent was also within the top ten local authorities with the highest proportion of its bridge stock deemed to be sub-standard.
The borough ranked sixth, with nine of its 40 bridges classified as too weak to be used by 44-tonne lorries.
Although sub-standard bridges were not found in any of the other north London boroughs – in total, Camden, Hackney and Enfield reported that more than £7 million would be needed to bring the stock of bridges and carriageways to a good, but not necessarily perfect condition.
This work amounts to £432,000 in Camden, £1 million in Hackney and £6 million in Enfield.
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.
Islington Council failed to provide data suitable for inclusion in the study.
RAC Foundation director Steve Gooding said: “This latest study shows the scale of the challenge local authorities are valiantly wrestling with to protect the critical road infrastructure we all rely on in the context of huge funding and resource pressures.
“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.”
Cllr 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.
“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 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.”
List of north London boroughs showing the number of bridges in each, with the number of sub-standard bridges in brackets.
- Barnet 72 (5)
- Brent 40 (9)
- Camden 8 (0)
- Enfield 192 (0)
- Hackney 14 (0)
- Haringey 42 (0)
- Harrow 14 (0)