A zero-alcohol limit for anyone under 20 who drinks and drives comes into force at midnight on Saturday night, and the police are confident it will alter the drink-driving behaviour of teenagers.
It is being introduced because teenagers are over-represented in crash statistics: in 2010 there were 60 road deaths involving drivers aged between 15 and 19.
The Government expects the new limit will save lives and lessen the burden on the health system.
National Road Policing Manager Paula Rose says the new law will reduce the number of teenagers who drive after drinking, and the Automobile Association agrees.
She says police will be out around the country on Saturday night conducting drink driving operations.
Ms Rose says devices have been changed to detect lower levels of alcohol, and police will take very firm action against anyone who is found to be over the limit for their age and stage of driving.
She says given the exposure the zero alcohol limit law has had, the police do not anticipate catching many teenagers.
Call for adult limit to come down too
The Public Health Association says the adult driving limit should also be lowered, as too many people die or are injured in alcohol-related crashes.
The association's national executive officer, Gay Keating, says: "Most of the high alcohol use and high alcohol damage is from old people.
"We see this as a step along the way to New Zealand understanding that alcohol produces damage no matter what your age is."
The Government has committed to two years of New Zealand-specific research into the level of risk posed by drivers with a blood-alcohol limit of between .05 and .08 - the current adult limit.