Polydrug use is one of the biggest challenges for most of our drivers on the road. It's very rare in samples that come through my laboratory section in toxicology that we see an individual drug. There are generally two or three different drugs involved in the samples that come through.
Most of the studies looking into fatalities show polydrug use. The roadside survey studies indicate a lot of polydrug use as well. One of the benefits of the DRE program is that officers are trained to look for polydrug use. They're taught how the different combinations of drugs will present, and what they should be looking for. Alcohol is separated out within the DRE, the drug recognition evaluation, by doing a breath test first to determine whether or not alcohol is playing a major role. If the person is blowing over 100, shall we say, then we probably would move over and do an alcohol impaired with the individual.
It's very common to find individuals who are providing alcohol levels of 30, 40, or 50 milligrams per cent who also have additional impairing drugs on board. Alcohol and cannabis particularly are a poor combination for driving skills, in that sub-impairing levels of either drug...that is, if you have a certain level of the drug and it wouldn't be impairing by itself, you combine them and you show much more impairment than you would expect to see.