The main section of the new A59 Kex Gill route between Harrogate and Skipton is set to open within weeks.
North Yorkshire Council says the majority of the new 4.2km road is expected to open to traffic by early September.
The £68.8million scheme will replace a section of the A59 which has been repeatedly affected by landslips, causing closures and lengthy diversions.
Since 2000, the existing road at Kex Gill has suffered 15 landslips, resulting in more than £6million being spent on repairs.
The majority of construction work on the new route is now complete, with work remaining on connections to the existing road network and road markings.
Once this is finished, two of the three carriageways will be able to open to traffic.
Cllr Malcolm Taylor, North Yorkshire Council's executive member for highways and transportation, said:
“The opening of the main section of this new route will be a landmark moment for North Yorkshire and for the thousands of people who rely on the A59 every day.
“For decades, this stretch of road has been vulnerable to landslips, leading to costly repairs, lengthy diversions and significant disruption for local communities, businesses and visitors.
“Within weeks, road users will begin benefiting from a modern, resilient route that is designed to serve the county for generations to come.”
The project is the largest highways scheme ever undertaken by North Yorkshire Council.
Lauren Luck, regional engineer at Sisk Infrastructure, said:
“We are delighted to reach this crucial milestone at Kex Gill.
“The project has presented significant engineering challenges, which our team and supply chain partners have successfully delivered solutions in very difficult terrain with significant environmental considerations to manage.
“We hope that this achievement creates a lasting, positive difference for communities across North Yorkshire.”
More than 12,700 native trees have been planted as part of the scheme, alongside wildflower planting, new habitats, balancing ponds and other biodiversity measures.
New routes for walkers, cyclists and horse riders are also being created, along with four kilometres of natural stone walls.
Work is continuing on the eastern and western connections, including a redesigned junction at Church Hill and improvements to access around Fewston Reservoir.
Once fully complete, the new route will take traffic away from the landslip-prone section of the A59 and provide a more reliable connection between Harrogate and Skipton.
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