An internal government study is warning that lowering the bar for drunk driving convictions could overwhelm the justice system.

The Justice Department study says courts, police forces and jails could be pushed to the breaking point if the federal government ever lowered the criminal drunk-driving threshold.

Ottawa is being pressed by Mothers Against Drunk Driving, the Centre for Addiction and Mental Health and others to tighten Canada's blood-alcohol limits for impaired driving.

But the department's criminal law policy section warns cutting blood-alcohol limits to level established in many other countries would likely double the number of cases in a justice system already struggling with a heavy caseload.

The current drunk-driving threshold is 80 mg of alcohol per 100 millilitres of blood, or point-08 per cent.

Drivers with levels above this threshold are subject to criminal charges and severe penalties, including jail time.

But the standard, set in 1969, is out of step with much of the world.

Australia, Germany, Italy and more than a dozen other states set it lower at point-05 per cent.

A copy of the draft report was obtained by The Canadian Press under the Access to Information Act.