The Maungatapu underpass will open to traffic on Friday, the New Zealand Transport Agency has announced.
Construction on the $45 million project started in September 2015.
A temporary 50km/h speed limit will apply to the 120m long underpass, which connects
Welcome Bay and Turret roads underneath State Highway 29A and the Maungatapu roundabout.
New traffic lights will be operating at the Welcome Bay Road and Welcome Bay Link Road intersection.
A temporary stop sign will be installed at Hairini Street. Drivers will be encouraged to use the access from the Maungatapu roundabout.
The separate shared cycleway through the underpass will not open until the Hairini Street connection is complete.
The access to Hammond Street from SH29A will be closed and access will be from the new Welcome Bay Road intersection.
While the main underpass was complete, there was still work to be done on connections with nearby roads, including Welcome Bay Road, Welcome Bay Lane, Hammond Street, Turret Road, Hairini Street and the Maungatapu roundabout.
Project Manager John McCarthy urged road users to take care when travelling through the underpass.
"We are nearing project completion, however the area remains a construction site.
As such, I urge people to take care and stay focussed when travelling through the area, for their safety, and the safety of their passengers and all other road users and construction workers."
The agency would not say what time the underpass would open for safety reasons.