Four-way temporary traffic lights have been put in place at the Weedon crossroads as work progresses on the scheme to improve the busy junction.
The changes at the A45/A5 intersection include extending the carriageway, creating additional lanes and installing ‘smart’ traffic lights to improve traffic flows.
The £950,000 scheme has been funded by the Government’s Growing Places Fund, which is designed to help push forward housing and economic growth.
The temporary lights are due to be in place until the end of October and motorists are being asked to consider using alternative routes, if possible.
A spokesman for Northamptonshire County Council said: “We are trying to minimise disruption as much as possible but inevitably there will be some inconvenience while such a big project takes place.
“We do apologise for any inconvenience caused.”