The New Zealand Transport Agency (NZTA) is vowing to push on with the $1 billion Transmission Gully highway between Wellington and the Kapiti Coast.
The Environmental Protection Authority yesterday gave final approval for the 27km inland highway, from Linden to MacKays Crossing, which will improve access to Wellington's port, business district, airport and hospital.
"This project has been talked about for nearly a century and this decision means we can put words into action," NZTA State Highway manager Rod James says.
The route is part of the Wellington Northern Corridor, from Levin to Wellington Airport, which has been identified as one of seven roads of national significance by the government.
Construction is expected to start in 2015 and finish in 2021.
Mr James says freight volumes are projected to double in the next two decades, and Transmission Gully is needed to support the growing population the region.
The route will also will make transport links between Wellington and the north of the country more secure and resilient in the event of a natural disaster.
Transport Minister Gerry Brownlee says the capital deserves better than a two-lane highway which has trouble coping in peak times and is vulnerable to closure if there are crashes or natural disasters.
The Greens sounded a sour note, saying it would be bad for commuters and the environment.
"It will undermine commuter rail, increase overall traffic in Wellington City and increase greenhouse gas emissions," said transport spokesperson Julie Anne Genter.
NZN