NZTA hopes a new road connecting Warkworth and Wellsford will reduce casualties from crashes on the route by 80 per cent.
It will also make travelling between Northland and Auckland safer, faster and easier, the agency says.
The motorway, to the west of the Dome Forest, will be completely separate from State Highway 1. It has been deemed a project of national significance.
Building a new road between the two regions is part of the Government's goal to create transport solutions that will help grow and support the Northland economy by connecting communities and moving freight efficiently.
The Dome Valley section of State Highway 1 was susceptible to flooding, slips and required ongoing repairs, NZTA's Northland director Ernst Zollner said.
Whereas the new road would "improve safety, reduce congestion and support Northland's economic growth".
Zollner said bends on the new road would be smoother than those on the existing highway - a design feature which the agency hoped would help to reduce the number of fatal and serious injury crashes by 80 per cent.
A barrier would divide north and southbound traffic and the road would have better passing lanes to improve safety and reduce congestion.
The route will allow trucks and heavy vehicles to bypass Warkworth and Wellsford, reducing traffic, noise and pollution.
Without the trucks 90 per cent less traffic will travel through the towns, making the roads safer for local road users.
Transport Minister Simon Bridges said improving the route between Auckland and Northland was part of the Government's plan to ensure the right infrastructure was in place to support and grow Northland's economy.
"It will reduce the overall travel time between Warkworth and Te Hana by bypassing town centres, and avoiding the steep and winding Dome Valley."
The planned route would connect local road network, joining the Pūhoi to Warkworth section of State Highway 1 near Kaipara Flats Rd, before continuing on the western side of the Dome Valley to Hoteo River.
At the river it would head east across the highway to an interchange at Wayby Valley Rd in Wellsford.
NZTA has also proposed that another interchange be built near Mangawhai Rd, so that the road can meet State Highway 1 north of Vipond Rd.
"Once the motorway is built travel will also be safer for local road users because 90 per cent of regional traffic, especially heavy traffic, can avoid townships making their main streets safer for motorists, pedestrians and cyclists," Zollner said.
Members of the public can provide NZTA with feedback about the proposed route and the agency will host five public information days in Warkworth and Wellsford.
People can also submit comments and feedback online at www.nzta.govt.nz/warkworth-wellsford.
If the project moves forward NZTA will apply for consent this year. The agency was yet to release a timeline for when the motorway will be constructed.
The public information days
• Saturday February 18 from 11am to 3pm at Warkworth Masonic Hall, Baxter St, Warkworth
• Tuesday February 21 from 3pm to 7pm at Wellsford District Community Centre, Matheson Rd, Wellsford
• Thursday February 23 from 3pm to 7pm at Warkworth Masonic Hall, Baxter St, Warkworth
• Saturday February 25 from 11am to 3pm at Wellsford District Community Centre,
Matheson Rd, Wellsford
• Tuesday February 28 from Te Hana Hall, Whakapirau Rd, Te Hana