The Transport Agency says better roading north from Wellington would make travelling out of the capital safer and more efficient.
On Monday the agency opened its case before a board of inquiry for consent to build a 13km, four-lane expressway from Peka Peka to Otaki on the Kapiti coast, bypassing the existing State Highway 1.
If built, the expressway would add to the already approved Kapiti expressway and contribute to the Government's plans for better links between Levin and Wellington Airport.
In seeking 49 resource consents for the $250 million project, the agency says the scheme is popular, will help efficiency and road safety, and will be shielded by trees where possible.
But opponents say it will blight the local environment and is being pushed through with inadequate consultation.
They say the four-laning of the highway further south makes extending the scheme to Otaki almost inevitable.
For the agency, lawyer Paul Beverly said it was a popular project. He said while 21 submissions opposed the development, 25 submissions supported it.
Mr Beverly said the existing SH1 doubled as a local access road and as a national through route, bringing congestion and compromising road safety.