A seized pin may have been to blame for the crack which forced the Forth Road Bridge to close, an investigation has revealed.
Engineers claim the crack on the bridge in Scotland would have appeared sooner were it not for the quality of the steel used to make the structure.
Engineering consultant Richard Hornby says the pin had probably been seized for years.
The suspension bridge was closed for almost three weeks after the problem came to light on 4 December, causing long delays for motorists.
It reopened to most traffic on 23 December, although HGVs are still not allowed to cross. Such vehicles will have to use alternative routes until at least mid-February.
No fault was found on the failed section despite 23 inspections since 2001.
Mr Hornby claims there was nothing in the inspection regime which would have discovered the seizure. He says o nly hi-tech structural health monitoring would have determined the fault.
The latest monitoring is to be used on the new Queensferry Crossing and is now in place on some sections of the Forth Road Bridge.
Installing the monitoring along the entire length of the structure from Edinburgh to Fife could cost up to £10 million.
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