MONTREAL - Drivers aged 21 and under are banned from motoring with even a drop of alcohol in their bloodstream as of midnight Saturday.

One expert who has helped sculpt the restriction said that the alcohol ban was initially proposed on all new drivers, but the government later amended it to aim only at the younger motorists.

"If we get on the site of an accident where there's been a fatality and it's a young driver, then in half of the cases this driver has alcohol in his or her blood," said Jean-Marie de Koninck, Quebec road safety expert.

The change was enacted as a way to deal with the fact that drivers under 24 account for approximately 10 percent of Quebec's driving population but are involved in about 25 percent of road accidents.

Those caught breaking the rule will lose their licenses for 90 days, face fines of $300 to $600 and lose four demerit points, a punishment which de Koninck considers a strong deterrent.

The group known as Mothers Against Drunk Driving applauded the measure.

"We know that it will save lives. We know that young people out there are driving impaired, they take higher risks," said Theresa-Ann Kramer, MADD spokesperson.

Similar other provinces already have youth motorist booze bans in place but the verdict is still out on their effectiveness, according to de Koninck.

And some youth organizations have denounced the measure, as it discriminates on people based on their age.

Kramer said that it's for their sake that the measure is being adopted.

"They represent a small percent of the population and are responsible for a large part of impaired driving crashes so therefore we have to target them because we want to keep them alive," she said.

CTV Montreal spoke to many people downtown, most of whom supported the measure.

"I think it's a good idea," said Kayla Pataki. "It gets younger drivers to wake up and realize that they're taking risks by drinking."

Correction: the original version of this story indicated that 21-year-old drivers were allowed to drink.