The deal has finally been signed and work on the Manawatū Gorge replacement road will begin soon.
The original gorge track connecting Ashhurst and Woodville has been closed since 2017 because of multiple slips.
But after almost a year of consultation, the $620 million project has been signed.
Transport Minister Phil Twyford was in Woodville for the official signing between the Alliance group designing, constructing and delivering the project Waka Kotahi NZ Transport Agency, Fulton Hogan, HEB Construction, Aurecon and WSP.
The 11.5km highway between the two towns will reconnect the Manawatū with Tararua District, Hawke's Bay and northern Wairarapa.
Twyford said it would restore the vital link for locals, travellers and businesses across the North Island.
"It will also help with the region's economic recovery," he said.
"The project will create hundreds of jobs and has a target to employ more than 60 percent local workers.
"This will have huge benefits for the region, with their people being upskilled and getting money in their pockets when they need it most," Twyford said.
Manawatū District Mayor Helen Worboys said knowing the new road was going ahead and had a start date would come as a relief to locals.
Worboys said the neighbouring towns had been struggling and hugely disrupted since 2017.
"For the communities either side of the old gorge road, Ashhurst and Woodville, those are the communities that have been hit really hard economically," she said.
"This is like a light at the end of the tunnel for them.
"There is a lot of work to be done yet, but at least they can see there is an end to this in sight. "
As part of the project, the Alliance is working with iwi, stakeholders and local government to ensure the surrounding environment is protected.
It said it would plant 46 hectares of native forest, rehabilitate 32km of streams, protect 48 hectares of existing forest and manage the pest control of 300ha of forest reserve.
The new route between Ashhurst and Woodville will include seven bridges and structures, and a shared path for walkers and cyclists.
Subject to consents, the enabling works will begin in October, while the bulk of the construction will start in January 2021.
The highway is expected to be open to the public by the end of 2024.
Locals in the area will be relieved when the shovels hit the ground after years of disruption.
The alternative route, The Saddle Road has more than 6000 vehicles a day drive it, coming through the main thoroughfare of Ashhurst at all hours of the day and night.