A stretch of the A6 will remain closed until the end of February, Highways have confirmed.
The road between the A14 at Rothwell and the B576 Harborough Road junction has been closed since Wednesday (January 18) after an inspection found safety issues with the bypass bridge.
It will now remain closed until the end of February following a review which has shown the issues to be more significant and the condition of the road is a safety risk.
A Highways spokesman said: “We are now starting works with all our partners and have specialist teams on site and plan to re-open the road at the end of February.
“The works we are undertaking will also be affected by adverse weather.
“All roadusers are advised to avoid the area or follow the signed alternative route.
“The diversion follows the most appropriate route and is for all vehicles as there are weight restrictions which must be observed.
“We would like to apologise for this extended closure and the inconvenience this is causing.
“Northamptonshire Highways is committed to safety and this route must remain closed until we feel it is safe to re-open.”
The signed route diverts traffic from the A6 onto the A427 junction towards Corby; traffic will continue along the A427 exiting at the A6003 roundabout. Traffic will continue along the A6003 (Uppingham road) to its termination at the A43 roundabout.
Traffic must then access the A43 (Southbound towards Kettering) and continue to junction 7 where traffic will leave the A43 and join the A14 travelling westbound towards Desborough and Rothwell.
Traffic will then exit the A14 at junction 3 to re-join the A6.