Northamptonshire County Council says the partial re-opening of a stretch of the A6 has been effective.
The A6 Desborough Bypass was closed in mid-January after problems were found near the bridge over the River Ise.
Further problems near a railway bridge saw the closure extended firstly until the end of April and then the end of August.
On Thursday (March 23) one lane from the originally-closed section was opened southbound on a trial basis, and the council says feedback has been good so far.
A council spokesman said: “The partial re-opening of the A6 Desborough bypass southbound has so far been effective in helping alleviate some of the traffic pressures in Desborough and Rothwell and feedback has been generally positive.
“It must be noted that the main diversion is still in place for through traffic and this is via the A14, A43, A6003 and A427 and vice-versa.
“Additionally we are going to increase advisory signs to promote the official diversion, particularly to heavy vehicles.
“We will continue to monitor the situation.”