First of all, I must make it clear that the person must have failed the roadside tests in order to be asked to come to the police station and undergo a breath analysis or a drug recognition expert's tests. If this person had taken a drug that makes him or her a better driver, the person will pass these tests without any problem.
Normally, the person's driving, for one reason or another, draws the attention of the police officer. The officer starts to discuss the problem he observed with the person. He will then notice something. It may be the smell of alcohol or of marijuana. It is possible that the person might start laughing or behaving bizarrely or unusually within the context of the discussion with the police officer. It is also possible that the person's eyes will not react normally.
That makes the police officer suspect that there may be drugs in the person's system. This legislation will allow police officers, under such circumstances, to do roadside testing. If the person fails these tests and the services of a drug recognition expert are available, the person will have to undergo that kind of test. This does not concern alcohol; you have to turn to an expert because that is needed to determine the presence of drugs. As far as mixtures are concerned, the seven drug families and their effects on a person, Corporal Graham should be able to tell us what the police officer would be looking for.