"They [the Government] really have not done any due diligence on this at all and I really am at a loss to understand why they have come up with this system," said Murphy, who fronted a campaign for the Motor Trade Association (MTA) demanding that the status quo be maintained.
"We have an incredibly old fleet of cars on the road and we are now putting the responsibility squarely on the motorist to ensure that they get their vehicles safe.
"It's things like tyres, brakes and suspensions that are the key things that concern us most. These things are meant to keep people safe on the roads and restrict hopefully accidents in certain situations ... not enough New Zealanders are aware of these little things."
MTA spokesman Ian Stronach said New Zealanders had been sold short.
With fewer inspections to be carried out, up to 2000 jobs would go in the automotive industry, meaning greater risks for motorists and an increase in costs for vehicle checks.
Mr Stronach said New Zealand had one of the oldest fleets of cars in the world, with an average age of 13.03 years, and many vehicles would now be travelling twice the distance and going twice as long before undergoing the minimum safety checks.
"In an automotive environment like ours, that is too long and too far. Minor repairs will turn into major work, negating any theoretical savings."
Vehicle Testing New Zealand chief executive Mike Walsh said the Government had "hugely underestimated" the additional costs the changes would bring.
"The Ministry of Transport's own figures predict an increase in injury accidents and even deaths, but we believe these figures have also been greatly underestimated. Some estimates predict an extra 10 deaths and 100 injuries on our roads each year."
There are about three million registered cars in New Zealand. The changes will affect 900,000 cars that will go from twice-yearly checks to annual ones.
WoF costs vary widely, but generally start at $45 for cars.
But Vehicle Testing NZ, which does nearly a million WoF checks and about 230,000 truck and trailer inspections a year, said the changes meant testing prices would "very likely" go up.
Mr Walsh said some of its testing stations might close and others might reduce their services.
Mr Bridges said the new regime recognised that the quality of vehicles and their safety features and performance were improving.
He said New Zealand had one of the highest inspection frequencies in the world and the changes brought it in line with other countries.
Automobile Association spokesman Mark Stockdale said the changes reduced unnecessary costs without compromising safety and would benefit at least 900,000 motorists.
"The arguments for retaining a six-monthly inspection are no longer as valid today as they were decades ago when cars were less safe and reliable."
The Government will work through options relating to information and education campaigns and police enforcement activities in the coming months.
Changes to the warrant-of-fitness system are expected to be in place by July next year at the latest.
Easing drivers' burden
The key changes to the warrant-of-fitness system include:
*An initial inspection for new cars, followed by annual inspections once vehicles are 3 years old.
*Annual inspections for vehicles 3 years and older and first registered on or after January 1, 2000.
*Six-monthly inspections for vehicles first registered before January 1, 2000.
*Information and education to increase people's awareness of regular vehicle maintenance.
*Extra police enforcement activities.
