The aeging Kopu Bridge has not been subjected to structural engineering checks since a 2001 report which said it could collapse in an earthquake.
The Transit study said "seismic deficiencies" would be "likely" to cause the single-lane bridge near Thames to suffer significant damage or "sudden collapse" even in a moderate quake.
Even though the 80-year-old structure - the gateway to the Coromandel for many holidaymakers - failed to meet modern safety standards, Transit said it was monitored by a "robust inspection strategy".
But it confirmed to the Herald on Sunday there had been no structural testing of the bridge or its piles since the critical 2001 report.
Coromandel MP Sandra Goudie obtained the report under the Official Information Act and asked further questions of Transport Minister Annette King in Parliament.
She said the Government should have funded a replacement bridge years ago.
"The longer the minister waits, the greater risk there is. How can Transit possibly say the bridge is structurally sound when it hasn't tested the structural integrity?
"The fact the 2001 report says a moderate earthquake would cause a collapse says it all."
Contemporary design standards require bridges to be able to withstand an earthquake of the magnitude experienced once every 2500 years.
Transit calculated the Kopu Bridge could withstand a quake felt once every 300 to 500 years but Waikato network operations manager Alan Burkett said the risk was "low".
He said inspections were designed to pick up any deterioration that would have an effect on the bridge's load-carrying capacity and safety.
The latest inspection report, from February, is only four pages long.
It says abutment bearings are corroded, timber handrails are in poor condition, with the deck cracking and steel corrosion throughout the superstructure.
Thames car dealer Ian Richardson raised concerns about the bridge after it was closed for urgent repairs in April.
Resulting publicity prompted Transit to commit to mid-2011 to start work on a $32 million replacement.
But the resource consents expire at the end of 2010, so Transit will have to ask the Waikato Regional Council to renew them.
Goudie and Richardson are calling on Transit to start sooner, but the agency says other projects are a greater priority.
Richardson said photos he had taken of the bridge's underside showed it was "falling apart".
He noted that while Transit had banned trucks from one of the clip-on lanes on the Auckland Harbour Bridge, the same trucks crossed at Kopu each day.
"Transit is just crossing its fingers and hoping that nothing happens. This could be a catastrophe, it's just nonsense," Richardson said.
King's office did not respond to Herald on Sunday questions before deadline. But in earlier reports, a spokesman said she was guided by engineering experts who said the bridge was sound. The spokesman said funding was allocated according to regional requests and the Waikato Regional Land Transport Committee had indicated the Kopu Bridge was not a top priority.
Transit was ready to build the replacement but the committee had indicated there were more important State Highway 1-related projects.