You're driving well under the posted speed limit on a two-lane highway with no safety reason to go that slowly, and a line of traffic is backing up behind you. Can this be a traffic offence, even though you aren't speeding?

Correct answer: B. Yes — driving needlessly slowly enough to impede normal traffic flow is itself an offence, unless the slow speed is necessary for safety

HTA Section 132(1) makes it an offence to drive "at such a slow rate of speed as to impede or block the normal and reasonable movement of traffic" — unless the slow speed is actually necessary for safe operation given the circumstances (e.g. fog, an icy road, a mechanical problem). There's no numeric floor; the test is whether you're needlessly obstructing traffic flow, not just whether you're under the posted limit.

Source: MTO Driver's Handbook: Highway Traffic Act, Section 132(1) — unnecessary slow driving