A Timaru mechanic says 60 per cent of vehicles through his workshop do not pass their warrant of fitness (WOF) test.
Murray Kitchen is the Motor Trade Association South Canterbury branch president.
He said, speaking independently of the organisation, that he feared the Government's move to requiring annual checks only could lead to a higher road toll, although it was a "wait and see" scenario.
"It will be interesting to see whether there are any WOF-related [issues] causing more fatalities."
Under reforms announced on Sunday, six-monthly warrants are to be phased out for cars registered after January 1, 2000, with only annual checks required.
Older cars will still require six-monthly warrants.
There will also be a more lenient regime for new vehicles, which will need an initial WOF but will then not have to be re-tested for three years.
Mr Kitchen said 60 per cent of vehicles he tested failed their warrant of fitness test, "whether it's just a lightbulb or a nail in a tyre or something more major".
"My concern would be that [a vehicle] that only just passed a warrant of fitness for whatever reason could be a potential hazard down the track."
He acknowledged vehicle safety had improved.
"[But] there's still the normal wear and tear things."
Mechanics were at the "coalface" and had a better idea of vehicle safety, he said.
Mr Kitchen did not believe the change would hurt business at his "two-man" garage.
"We're busy as. I don't know that it's going to affect me at this stage."
Prime Minister John Key defended the changes at the weekend, saying they would save time and money.
The changes will affect about 1 million of the 3 million cars in the country, and will come into force in July 2014, or earlier.
"I think it's going to maintain safety standards and its just a sensible move forward," Mr Key said.
The Government has earmarked between $2.5 million and $5m extra for the police to implement the new warrant of fitness regime that will include stronger enforcement and roadside checks.
WOF testing was introduced in the 1930s and car design had come a long way since then, Mr Key told RadioLive.
Ministry of Transport research showed the changes would benefit motorists and businesses by $159 million a year, and by at least $1.8 billion over 30 years.
Labour spokesman Kris Faafoi has called for the Government to explain just what officers will be checking.
"I think Kiwis want to see police spending most of their time preventing and fighting crime, not checking indicator lights, wiper blades and tyre treads," the Mana MP said.
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