The A6 won’t fully re-open until the end of August, after damage to the carriageway leading to a railway bridge was found to be worse than expected.
But motorists who have faced huge diversions will get some respite from tomorrow with one lane set to open on a trial basis.
The stretch over the River Ise has been closed since mid-January and was set to open by the end of February, until further investigations revealed more problems and voids near the railway bridge.
Northants County Council – which has spent £500,000 so far on repairs – extended the closure and delayed the opening date to the end of April, but that has now been extended until the end of the summer school holidays.
Cllr Ian Morris, cabinet member for transport, highways and environment, said: “Extensive survey work has been carried out and carrying out repairs on the road where it joins the railways bridge is much more complicated than initially thought.
“We have no option but to keep the closure in place for longer than we initially anticipated so that the work can be done properly.”
The southbound lane of the A6 from Braybrooke Road to the A14 will now re-open to the public tomorrow after the morning rush hour to relieve traffic pressure in Desborough and Rothwell.
This will be on a trial basis and will be monitored by the council.
Cllr Morris added: “We are aware of the effect that the closure has had on the local community and that is why we have decided to trial the opening up of a section of the A6 in an attempt to alleviate some of the traffic pressure.
“We would like to thank people and businesses in the local communities for their patience while this situation continues.”
The official diversion will remain in place but none of the work near the railway line will affect passenger trains.
Operations manager Leon Jolly said they have explored all possibilities to re-open the road, even partially, but the voids are too significant.
He added that they are doing everything they can to open the road fully before their target of the end of August.
He said: “We are looking at every possible option to open it earlier.
“Every solution has been looked at.”
The council has been in discussion with the Government over funding and is still waiting for feedback.
Mr Jolly said they cannot put a figure on the overal cost of repairing the road yet – but their focus is just on getting it open.
He said: “It’s difficult to tell you the exact cost.
“At the moment we are focusing on getting the road open to the public.”