MTA says Government needs to be aware that average age of cars varies widely from region to region.
Motor industry lobbyists are citing "huge" regional variations in the ages of vehicles on New Zealand roads in their campaign against any loosening of the existing warrant of fitness system.
Although the average age of the national fleet is 13.03 years, Government statistics reveal a wide range from 10.3 years in central Auckland to 16.8 years in Waimate in south Canterbury.
That has prompted the Motor Trade Association, representing repair workshops and service stations, to warn policy-makers to think twice before changing the existing requirement for six-monthly warrants of fitness for any vehicle more than six years old to be allowed to stay on the road.
The warning comes as the Government is expected to choose in the next fortnight from four potential alternatives, such as annual inspections for the first 12 years of a vehicle's life, as favoured by the Automobile Association and about 70 per cent of its members.
Although Australian university researchers believe that could save motorists up to $250 million a year, the MTA warns it could be at the cost of 80 more annual road deaths.
That is strongly disputed by the AA, which says mechanical defects are implicated in only 2.5 per cent of vehicle crashes and are the sole cause of just 0.4 per cent.
MTA spokesman Ian Stronach says the national average vehicle age of 13 years, high as it is by international standards, did not disclose the true state of the fleet outside the main centres of Auckland and Wellington, where many people use company cars "and most of the drive for regulatory reform comes from".
"There is some very old iron out there," he said yesterday.
"New Zealand's average vehicle age belies regional variations and many of the vehicles outside of the main cities are much older and have many fewer modern safety features.
"This isn't just about driving a new car with all the mod-cons - the increasing number of old, often poorly-maintained, vehicles has serious safety implications for anyone who travels on the roads of New Zealand."
Mr Stronach said vehicle ages tended to increase the further south they were found, although the average for the Kaipara, north of Auckland, is 14.5 years, and Hauraki is 14.8.
"I think what you are seeing here is a lack of buying power of New Zealanders - we are not a high-wage economy and you can see that outside the main centres."
He noted that even the national average was too high by international standards, ranking against 10 years in Australia, 10.8 in the United States, 7.4 in Britain and 11.8 in "that hotbed of modernism, Russia".
But AA spokesman Mark Stockdale said that regional variations were not the whole story.
"We've got to keep in mind that in the last few decades the quality and reliability of the fleet has improved out of sight.
"Back in the 1970s, people were driving around in 20 or 30-year-old cars routinely."
He said the national average was "skewed" by a high number of cars made in 1996, to beat looming changes at that time to vehicle emission standards.
These were nearing their end of life "so when they leave the fleet the average age will drop noticeably".
They would meanwhile continue to be covered by six-monthly checks if the Government adopted the AA's preference for an annual inspection cut-off at 12 years.