This policy brief is one of a series on current topics related to impaired driving in Canada. Other topics include oral fluid drug screening, administrative sanctions and drug per se laws. The briefs are not intended to provide a comprehensive and critical review of the literature. Rather, their purpose is to provide a balanced overview of the issue, including a description of any procedure or process involved, an indication of similar measures in other countries, evidence of the effectiveness of such measures, and potential limitations and alternatives. The policy briefs are intended for a broad audience of persons interested in impaired driving issues. Those interested in learning more are encouraged to consult the additional resources listed at the end of the report.