Hundreds of homes, businesses and rural properties are in the path of the $1.4 billion Mill Rd highway in South Auckland.
Engagement with about 600 landowners is to begin shortly on a preferred route between Papakura to Drury, according to a briefing paper from the NZ Transport Agency to incoming Transport Minister Michael Wood.
One of the landowners is Kāinga Ora, which owns land and homes in the vicinity of the route through Papakura.
A spokesman for the housing agency said it was aware of the highway when it bought land in 2019 and saw the transport project working well for its current and future developments.
Kāinga Ora could not comment on the possibility of losing some of its land, the spokesman said.
Those details would need to come from NZTA when its plans were finalised, he said.
Papakura local board chairman Brent Catchpole said the board supported the highway, but said it was going to be very difficult for NZTA to deal with property owners.
From what he knew, Catchpole said, the highway would have a big impact for homeowners in Papakura east, and was likely to affect a new subdivision at Twin Parks, where about 150 homes were completed in 2016, and a nearby early childhood centre.
It could also cut through Kerri Downs park in Papakura where kilikiti - a form of cricket popular among Pacific Islanders - was played, Catchpole said.
He said the project had been on the books since before the Super City was formed in 2010, and a firm decision on the designation was needed to give homeowners certainty.
The northern section of the highway between Redoubt Rd in Manukau and Alfriston Rd north of Papakura had already been designated, but there would be a "significant impact on private property" on the southern section, an NZTA spokesman said.
The southern section runs from Takaanini, around the east of Papakura to Opaheke and Drury where it connects to the Southern Motorway.
The project, which upgrades Mill Rd from two to four lanes with separate walking and cycling facilities, is part of a $2.4b Government investment in new roads and rail in South Auckland.
The quiet community of Drury, population 4960, will be turned into a city bigger than Napier, with tens of thousands of new residents, two new railway stations and an electrified rail line from Papakura to Pukekohe.
All up, the 21.5km highway will support an extra 120,000 people in South Auckland over the next 30 years.
The plan is for Mill Rd to be used for local trips and reduce traffic on the Southern Motorway, running parallel to the new four-lane highway scheduled as a "Road of National Significance" by the former National Government.
The NZTA spokesman said Mill Rd was a complex project and work was still going on to confirm where the Takaanini, Papakura and Drury sections would go.
"The size and scale of this new corridor, combined with the fact we are building large sections through established areas means that no matter the route chosen, there will be significant impact on private property.
"We are taking the time to ensure we make the right decisions, and that means we have not confirmed the preferred route south of the Manukau section, including the number of properties potentially impacted," the spokesman said.
He said engagement had not begun, but NZTA had written to landowners in the Mill Rd area to update them and let them know there would be a further update in 2021.
"Currently, the project team is undertaking site investigations in the area, which includes ecological, topographical, geotechnical and general surveys and this work will continue for several months. We had planned to carry out these investigations earlier in the year but had to delay this work due to Covid-19," the spokesman said.
Mill Rd is part of the Government's NZ Upgrade Programme released earlier this year. Construction is due to start in late 2022, and the highway will be built in stages through to 2028.