It would be unrealistic to bar drivers from having any trace of marijuana in their system when it becomes legal in Canada, as B.C. has suggested, because the drug can be detected long after a person is impaired, public-health experts say. The federal government’s task force on the future of legalization has highlighted impaired driving as one of the core issues it must address before making its recommendations by the end of this month. (See also: Drugged driving: Shaky science and uncertain laws)