He said minor mechanical details that were picked up at six-monthly checks could become big problems if left for a year.
"Instead of having a $100 bill, it's several hundred dollars."
Mr Head said the warrant changes were "bizarre" given the state of many Northland roads.
"It's not so bad driving in some places like Auckland, but I feel sorry for those guys driving on the roads somewhere like Panguru, for example."
But the Automobile Association says few accidents are caused by vehicle defects, and it is welcoming the WoF changes as cost-effective for motorists.
John Olley, manager of the AA in Whangarei, said the less-frequent warrants made sense for people who had newer cars. "Most new cars came with free servicing for the first three to five years anyway."
And there were older cars with few kilometres on the clock whose owners did service them regularly, who would fly through a yearly warrant check with no problems, Mr Olley said. Fears about car modifications happening in between yearly warrant checks were unnecessary, he said. "You're never going to stop the people that take their cars in for a warrant check and then change them."
But Mr Olley said there would need to be more education for motorists around checking for things such as tyre tread that needed to be kept up to scratch, and he hoped police would be given more support if they were expected to conduct roadside checks.
WoF changes from 2014
Vehicles more than 13-years-old will still need six-monthly Warrant of Fitness checks .
Vehicles aged from 3 to 13-years-old will only require annual WoF checks.
New cars less than 3-years-old won't require a WoF.
Police would carry out more vehicle roadside checks of things such as brakes, lights and tyres.
A refinement of the certificate of fitness and vehicle licensing.
What do you think of the proposal?
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