A fire department vehicle is responding to a fire alarm, well above the posted speed limit. Do HTA speed limits actually apply to it in that moment?

Correct answer: D. No — while responding to the alarm, it's exempt from the posted speed limits

HTA Section 128(13) says the speed limits set under this section (and any by-law or regulation made under it) do not apply to a fire department vehicle proceeding to a fire or responding to a fire alarm or other emergency call (but not while returning from one), a police vehicle in the lawful performance of duty, an ambulance responding to an emergency call or transporting a patient in an emergency, or a Ministry vehicle used by an officer carrying out the Act. The exemption is conditional on the specific circumstance — a fire truck returning from a call, for instance, is not covered.

Source: MTO Driver's Handbook: Highway Traffic Act, Section 128(13) — speed limit exemption for emergency vehicles