Traffic injury researchers say they aren't convinced lowering the legal blood-alcohol limit will keep drunk drivers off the road.

Federal Justice Minister Jody Wilson-Raybould has been floating the idea of changing the law to only allow 0.05 milligrams of alcohol per 100 millilitres of blood, down from the current limit of 0.08 milligrams.

In a letter to provincial ministers, Wilson-Raybould said the change would help keep drunk drivers off the road, but an Ottawa-based traffic fatality expert says it may not be that simple.

"A lot of the drinking drivers in fatal crashes, more than half of them, have a BAC (blood-alcohol concentration) of 0.16, so double the legal limit," said Robyn Robertson, president of the Traffic Injury Research Foundation.

Robertson told CBC Radio's All In A Day that one per cent of all drunk drivers cause half of alcohol-related fatalities on the roads, and that it's the "persistent drunk drivers" causing the majority of collisions.

"We have to understand where the largest proportion of our fatalities are coming from," she said.

The traffic research Robertson's foundation conducts has found that about 75 per cent of drunk drivers are well over the current legal limit when they're stopped.

Police presence is key

In order to really clean up the roads, Robertson said it would take more than changing the law.

"Impairment begins at a much lower BAC level than .05," she said, adding that a significant police presence is one of the best ways to deter impaired drivers.

"Enforcement has such a difficult job. We have a limited number of officers, [but] we have to be able to enforce it. We have to be able to follow it through the criminal justice system," she said.