Official papers show people using Mount Victoria tunnel in Wellington were at risk, until recently, of being hit or crushed by falling concrete.
A report prepared for the Transport Agency in July last year showed the risk of an false ceiling collapsing in the tunnel before the middle of next year was high.
Four areas were in poor condition, pieces of concrete could potentially break off at any time, and there had been a one in 60 chance of it failing between 1974 and 2010.
The false ceiling was taken down recently during an upgrade of the tunnel.
The Mount Victoria Residents Association says that if NZTA knew of major problems last year it should have told the public and closed the tunnel for repairs immediately.
President Elaine Hampton it's shocking that users were not told.
But NZTA Wellington state highways manager Rod James says there was no need to close the tunnel or tell the public, because the risk was not high enough.
He says other tunnels around New Zealand don't have the same type of false ceiling.
The 625 metre tunnel was built by Wellington City Council to link the central city with the eastern suburbs.
It was opened on 12 October, 1931 and is now part of State Highway 1 and the main route to Wellington airport.