Northamptonshire County Council says work on the A6 Desborough bypass is on track to be completed by the end of August.
Problems with the road first came to light in mid-January, when an inspection found foundation failures with the bridge crossing the River Ise.
That work has now been completed, but further inspections found issues with the stretch on the approach to the railway bridge.
That meant, much to road users’ frustrations, that the full re-opening was put back until the end of the summer holidays - although the southbound lane of the A6 from Braybrooke Road to the A14 is now open again.
A spokesman for Northamptonshire County Council said: “The problems found on the carriageway leading on to the railway bridge are more severe than at the River Ise Bridge and there are logistical problems in carrying out repairs over a live railway line.
“We are working closely with Network Rail and all associated parties, including specialist contractors, to develop and implement the repairs.
“The works require significant co-ordinated planning because of the proximity to the Midland Mainline.”
The spokesman added that the work schedule is still on target and thanked people for their patience.
He said: “Preparatory works are ongoing.
“We are amending the design of the repairs so we can operate within the times available to us – known as track possessions - to help eliminate any impact on rail users.
“The works are currently still on target to be completed by the end of August.
“We would like to take this opportunity to thank everyone for their understanding and patience while this work continues.”