Police officers across Canada are undergoing intensive training on how to spot drug-impaired drivers.
While police can conduct a breathalyzer test to determine whether a driver is drunk, there is no proven scientific test to measure drug use that would hold up in court.
Drug tests are also inaccurate -- studying a driver's blood sample may reveal traces of marijuana, but it cannot offer specific details on when the drug was inhaled.
To overcome that problem, police are now turning to an enhanced version of and old-fashioned method: the walk-the-line test.
At a training program in Ottawa this week, officers watched as a group of volunteers drank alcoholic beverages.
They then studied the visual signs of impairment, as the inebriated participants performed actions like tracking a moving object with their eyes.
"The program we're doing now will enable us to deal with drug-impaired drivers the same way we deal with alcohol-impaired drivers," RCMP Cpl. Evan Graham told Â鶹´«Ã½.
But critics said the tests could still be problematic in court, if justice officials decide they only provide weak evidence of drug use.
"I think there's going to be a large area of uncertainty, until we see the quality of the graduates and how it's actually going to be enforced in the field, as opposed to the classroom," said defence lawyer Bruce Daley.
Under legislation proposed by the Conservatives in the last session of Parliament, police would be able to force drivers to take the test.
But because Prime Minister Stephan Harper prorogued Parliament, the bill will now have to be re-introduced.
The Canadian Safety Council estimates that 500,000 Canadians in any given year smoke marijuana and drive.
With a report from CTV's Graham Richardson in Ottawa
