Yes, it is. The tests are done roadside to elevate suspicion to reasonable and probable grounds.
As far as the Supreme Court ruling on whether or not it's incriminatory is concerned, if we're using it just to elevate the suspicion to grounds for a breath demand, we're not required to provide the charter warning. If we're trying to equate what we're seeing with a level of impairment, then the person has to be given the right to counsel, because it become incriminatory or self-incriminatory.
Weather-wise, it's certainly an issue in Canada, because of our climate. But of the studies done in the United States, one was done in Colorado year round. So they ran into exactly the same problems we'd run into here with snow, uneven road surfaces and inclement weather. And despite the poor weather conditions on some nights, the tests were still validated; they still showed that they worked.
And again, we're talking about elevating suspicion to reasonable and probable grounds for a breath demand. If the person comes back and either blows under the legal limit or there's no alcohol involved at all, then the person would be released.