The Transport Agency says a second tunnel under The Terrace in Wellington to help streamline inner city traffic is on the cards.
It would be in addition to a second tunnel under Mt Victoria, but would come later.
NZTA has applied for resource consent to build a flyover beside the Basin Reserve and revealed more details of its second tunnel under Mt Victoria.
There would also be wider roads from the Mt Victoria tunnel towards Wellington airport and the entire process would be done by 2022.
But the agency acknowledges there could be traffic bottlenecks in the city leading to the flyover.
It said fixing these would involve a second tunnel under The Terrace and clearways and improved intersections on Vivian St.
The agency said it has only just started investigating the project and work is scheduled at this stage for 2024.
Opponents vow to continue flyover fight
Opponents of a plan to build a flyover near the Basin Reserve in Wellington will continue to fight the project.
The Transport Agency announced on Tuesday it has filed a resource consent application for the bridge and hopes construction will be completed by 2017.
NZTA said the flyover and other roading projects in the city will cut travel times to Wellington airport and remove an obstacle to economic growth.
But Wellington City Council member Iona Pannett said the case for the flyover is deeply flawed and concerns about congestion are overstated.
Cr Pannett said building the flyover will only encourage more people to drive to the city when the agency should be promoting public transport, cycling and walking.