On the approach to a freeway entrance ramp, a yellow sign reads RAMP METERED WHEN FLASHING and its amber lights are going. What should you be ready for?

Correct answer: D. A signal partway along the ramp that will require you to stop before merging — the flashers mean metering is in effect now

To stop on the ramp. Book 6 says this sign "may be used at freeway ramp metering installations, to warn drivers when ramp metering is in effect", and gives the reason for warning at all: "drivers unfamiliar with ramp metering operations, or drivers not expecting ramp metering at a given ramp, may not be prepared to stop, and hence a warning is appropriate." A metered ramp carries a signal partway along it that releases vehicles onto the freeway a few at a time, so the queue in front of you will stop and start rather than accelerate away. The flashers tell you the metering is running now — with them dark, the ramp behaves normally.

Source: MTO Driver's Handbook: Ontario Traffic Manual, Book 6 — Warning Signs (July 2001), Section 6 — RAMP METERED WHEN FLASHING Sign (Wb-7, with amber flashers)