The green light has been given for the Transmission Gully roading project, as part of improvements to the Wellington northern corridor.
The corridor, identified by Government as one of seven roads of national significance, will be developed as a four lane expressway from Levin to Wellington international airport over the next decade.
The Transport Agency says the proposed 27km route from MacKays Crossing - Linden, is a better choice than an upgrade of the Coastal Highway.
Chair Brian Roche says Transmission Gully is less expensive, will provide a safer four lane route, is better for local communities and the environment, and will reduce travel times between Kapiti and Wellington.
The $1 billion route has been mooted for more than 50 years.
The agency says it's investigating options for alternative funding, including tolling.
The agency also announced the preferred option for the route of an expressway at Kapiti route, which is also part of the northern corridor.
The Western Link option, which was initially not considered, has been chosen because it's the least expensive option.
Mr Roche says it will deliver the best results and will require the purchase of the smallest number of houses. It also avoids town centres.
The agency says the focus for the Wellington northern corridor over the next three years will be on designating land for improvements and providing certainty about what is to be done and when.
Some 650 jobs are expected to be generated as a result of the projects.
The agency also announced a preferred route for a four lane Kapiti expressway, second tunnels for Mount Victoria and the Terrace and an additional lane at Ngauranga Gorge.
Work will also be undertaken to separate lanes at the Basin Reserve as well as a dual carriageway from Peka Peka to Levin.
Senseless, say Greens
The Green Party says it makes no sense to go ahead with Transmission Gully.
The green light has been welcomed by Labour and United Future. who say it will provide a much-needed alternative route in and out of the capital.
But the Greens' Wellington transport spokesperson Sue Kedgley says it won't provide Wellington with a secure alternative route in the event of an earthquake.
She says part of the new motorway would be built on a fault, and if there is an earthquake, it could take three weeks to clear.
Ms Kedgley says the roading upgrades as announced on Tuesday will increase traffic congestion and result in a drop-off in passengers using public transport.
United Future leader Peter Dunne says Transmission Gully is the best, and only, option for improving access to the capital.
Mr Dunne who is the MP for the Wellington electorate of Ohariu, has campaigned for Transmission Gully, and says it's a red-letter day for the Wellington region.