Some Kapiti Coast residents and local Maori are considering legal action to block the construction of an expressway.
The Environmental Protection Authority on Friday issued the independent Board of Inquiry's final decision approving the controversial road near Wellington after hearing more than 700 public submissions during a 27-day hearing.
Construction of the $630 million four-lane road linking Mackay's Crossing to Peka Peka is likely to start in July this year.
The Kapiti Coast District Council and local chamber of commerce support the proposal, but there has been widespread opposition from residents and iwi whose land the 16km expressway will run through.
Bianca Begovich, from the Save Kapiti group, said on Friday they will continue their campaign against the highway.
"The fight is not over - this project simply must not go ahead. It's such a bad idea and is of so little benefit to the majority of taxpaying New Zealanders. It only benefits a select few in the trucking, infrastructure and banking industries."
The Takamore Trust said local Maori are unlikely to ever give the road their blessing because it passes within five metres of a burial ground.
Environmental youth group Generation Zero says the project is a waste of taxpayer's money which would be better spent investing in public transport. The group says it will hold protests around the country next week opposing the decision.
A new road for the Kapiti Coast to ease congestion on State Highway 1 has been planned since the 1950s. The expressway is part of the Government's $11 billion Roads of National Significance programme and the Transport Agency wants to eventually extend it further north to Otaki.
Kapiti Chamber of Commerce chairman Mark Ternent says there are some valid concerns about the road.
"At the end of the day though, I think most people support the idea that the current road is inadequate. It's inadequate now, it's inadequate for future growth, it's unsafe and it'll be great to see a new road being built."
The Kapiti District Council says people now have 15 days to appeal against the decision in the High Court. Appeals can only be based on points of law, not on the decision itself.