Police have been issuing a maximum of 235 tickets a year to motorists whose cars have smoky exhausts.
According to figures obtained under the Official Information Act, between 200 and 235 tickets a year were issued between 2005 and 2008 to drivers whose vehicles emitted excessive smoke or vapour for more than 10 seconds.
And in 2009, just 138 people were given the instant fine of $150.
National Road Policing Manager Paula Rose says it isn't always appropriate to issue tickets for smoky vehicles and owners could be given a verbal warning instead, or a fine for other offences.
Superintendent Rose says smoky vehicles often have no warrant of fitness or certificate of fitness, and owners will be fined for that offence instead.
She says another option is to follow motorists to businesses that fix exhaust faults.
However, the Automobile Association and the Green Party say more fines should be imposed because there are a lot of smoky vehicles on the roads.