Gridlock is predicted by the Mt Victoria Residents Association in Wellington if two inner-city tunnels on State Highway 1 are closed for maintenance during the summer holidays.
The Terrace and Mt Victoria tunnels could be closed for up to five weeks so the Transport Agency can remedy fire risks as part of an $80 million upgrade.
The agency is looking at complete closure of the tunnels after Christmas, or shutting them at night.
It says the need for an upgrade follows an investigation that found below-standard ventilation, internal cladding, lighting, drainage, fire suppression and emergency systems.
However, the Mt Victoria Residents Association says the closure could mean increased use of the Hataitai bus tunnel.
Acting president Kent Duston says the tunnel is old and narrow, but cars and people still use it even though it is meant for buses only.
Other residents associations say they are disappointed the agency has not consulted them yet on the traffic implications.
The agency says it will meet residents associations before a timetable is finalised for starting the work.