OAD engineers are blaming the weather for delays prolonging the journey of motorists using the A66.
Work started in March last year on a £14.3m contract to replace Surtees Bridge which carries 55,000 vehicles a day over the River Tees at Thornaby, with a new, wider three lane span.
The work was forecast to last 19 months and a 30 mph enforced speed limit has been in force both ways ever since.
But Arun Sahni, (COR) project manager for the Highways Agency, last night revealed the work will take longer than first anticipated.
He said: "Work on Surtees Bridge has been extended and completion which was due in late summer will now be in early Autumn.
"This is as a result of weather conditions impacting on the availability of equipment such as the large crane needed to manoeuvre new deck sections."
He says many drivers using the bridge will be unaware that the whole of the original structure has already been demolished and replaced.
Mr Sahni said: "People think they've been driving on the same bridge all this time
but in fact, it is now a completely new structure
"The way the new bridge has been designed has allowed us to completely dismantle the old structure whilst building the new structure alongside and keeping traffic flowing.''
Work began after studies showed problems with the old concrete bridge supports below the water line and with ground conditions on the east embankment.
The further delays will put a further month to the time to finish the bridge and open the slip roads to and from the new South Stockton.