The Government is investing £60 million in the A361, a key road linking Devon with the rest of the UK, with work expected to start this month.
The major project, which is being led by Devon County Council and will cost £67.6m in total, is expected to boost the local economy by supporting plans for 6,700 new homes in the region and increase cross-country connectivity by improving people’s ability to travel into and out of the south-west.
Works will focus on a 4.8 mile stretch between South Molton and Barnstaple.
The route will be modernised with a wider carriageway, which aims to improve overtaking opportunities, safety and resilience.
The road’s capacity and eight key junctions will be upgraded.
Facilities for pedestrians and cyclists will also be introduced along the route to encourage active travel.
Transport Secretary Grant Shapps said: "I’m delighted to announce this funding to upgrade a vital gateway between Devon and the rest of the country. These works will boost connections, cut congestion for drivers and improve people’s quality of life.
"It’s a clear indication of our commitment to levelling up and investing in transport infrastructure. Through these works, we’ll improve people’s ability to travel across the south-west while providing thousands with greater access to new homes and new jobs."
Councillor Andrea Davis, Devon County Council Cabinet Member for Infrastructure, Development and Waste, said: "This announcement is fantastic news for local residents and for Devon’s economy.
"The upgrade of this road is the biggest transport investment in north Devon for a generation.
"It will help unlock the true potential of the local economy in northern Devon, and with the ongoing impact of the coronavirus pandemic, that’s vital at this time.
"We’ve been working tirelessly on this project for a number of years so it’s great to see that effort rewarded with this government funding. We’ll now be looking to get work started as soon as we can."
Improvements to the A361 are the latest boost to transport in Devon, following the opening of the first phase of a new £80 million sea wall at Dawlish by Rail Minister Chris Heaton Harris in September.