A new £41m bypass which will divert traffic away from three villages has officially opened.
The A45 link road between Northampton and Daventry avoids Nether Heyford, Flore and Weedon.
It runs parallel with the M1 from junction 16, crossing the Grand Union Canal, the West Coast Mainline and the A5 before rejoining the old road.
Kamaljit Khokhar, from Highways England, said it would "unlock the potential for new jobs and homes".
The 3.5-mile (5.7km) route was supposed to open earlier this year, but was delayed due to poor weather.
Northamptonshire County Council said the "prolonged and very cold winter" in 2017, and torrential rain followed by extreme heat this summer, caused "unavoidable" disruption to the work.
Ian Morris, the councillor responsible for highways at the Conservative-controlled local authority said: "Not only does it [the new road] improve transport links but it also helps unlock housing growth in the Daventry area.
"But perhaps most importantly it is the people in the nearby villages who will be thrilled to have this road which will make their communities safer."
The work has been funded by the SEMLEP Local Growth Deal, the Highways England Growth and Housing Fund, Northamptonshire County Council, Daventry District Council and developers.