Transport for London has revealed that safety checks uncovered structural weaknesses on the 190m long A41 Brent Cross flyover in Barnet.
The roads body is now trying to secure £50m of funding from the Department of Transport to fund emergency remedial works after imposing a 7.5t maximum weight restriction on the dual carriageway structure.
A TfL spokesman said: “While previous assessments had shown the flyover to be safe, a number of additional safety checks were carried out during the development of a refurbishment project.
“These additional checks showed the maximum weight that the structure is able to carry is lower than previously assessed.
“While the flyover does not pose any immediate risk to people using it, these new measures are being introduced to avoid any further damage to the flyover while TfL works to resolve the issue as quickly as possible.”
He added: “This includes work on a project that will renew a number of major structures in the area.
“TfL continues to work closely with the Department for Transport to secure up to £50m funding for this project from its Major Road Network Programme. ”