WELLINGTON A proposed zero blood alcohol limit for young drivers shouldnt pose problems for teenaged communicants driving home after Mass, the president of the Police Association says. Greg OConnor told NZ Catholic he would be very surprised if it was an issue.

Transport minister Steven Joyce announced last month that a plan to reduce the blood alcohol limit to zero for drivers aged under 20 would be taken to Cabinet for consideration.

The limit now for young drivers is 30mg/100ml. The adult limit is 80mg/100ml.

Mr Joyce referred to research showing even a small amount of alcohol meant young drivers had a higher risk of crashes. He expected legislation to be in place by the end of the year.

But Mr Joyce also said some leniency would be shown for young drivers with very small amounts of alcohol in their system.

After NZ Catholic asked the Police Association if police would have to exercise discretion in the matter, as they have to with anti-smacking laws, Mr OConnor said that would be the case.

It will generally be a Sunday morning issue and probably a police officer would be able to work out if someone had just come from Mass or if they were on their way home from an all-nighter, he said.

Mr OConnor said the matter could be raised by Church representatives when a parliamentary select committee considers future legislation.

But Parliament won't want to create a Catholic defence for any young driver whose blood alcohol is too high, he said.

Mr OConnor anticipates potential problems in detecting absolute zero alcohol measurements and notes that some medicines like cough mixtures contain small amounts of alcohol, too.

There are always unintended consequences of every law change and informed people going to select committee should give lawmakers the opportunity to reduce the unintended consequences, he said.

Mr OConnor said many countries have zero alcohol limits for young drivers and he wondered if a sip of wine from the chalice would register on measuring equipment.