A road in Thrapston has had to be closed at short notice.
Scheduled repair work to the Nine Arches bridge between Thrapston and Islip was expected to take place with vehicles still able to use the road.
Traffic lights were to be put in place to control the flow.
However, once work started it became clear that the scaffolding was sticking out too far into the road and the decision was taken to close the road to traffic completely.
A spokesman for Northamptonshire County Council said: “Repair works are being carried out on the Nine Arches bridge between Thrapston and Islip.
“To carry out the works, permission had been obtained for a seven-day-a-week 24-hour road closure, to be used on occasion if necessary.
“To minimise disruption it had been decided to do the majority of the work under two-way traffic lights, allowing repairs to be done while keeping traffic flowing.
“However since work started, it has been recognised that the scaffolding that was required encroaches on to the highway and that, for the safety or the workforce and road users, it is not safe to continue to work in the original way.
“Diversions in place are to the east or west out of Thrapston and Islip respectively to then travel between junctions 12 and 13 of the A14.
“We are liaising with bus companies who will be following the diversion.
“Now the closure is in place 24 hours a day, this means that the work can be done more quickly and at weekends.”
Pedestrians can still use the footbridge.
The work is expected to last for seven or eight weeks.