PassReduced Visibility
Where: Directly beneath another regulatory sign, on roads where fog, mist, smoke, dust or sea haze is a recurring problem — mountain passes, coastal stretches and valley roads in particular.
Purpose: To limit when the sign above it applies. A supplementary plate never carries a message of its own: it qualifies the sign it hangs beneath. This one says the restriction above applies when visibility is reduced.
Action Required by Driver: Read the pair together, never separately. If the sign above shows a lower speed limit and this plate hangs below it, that lower limit binds you whenever visibility is poor — and in clear conditions the ordinary limit applies instead. Judge the conditions honestly: the plate does not define a threshold, so if you cannot see far enough to stop safely, visibility is reduced.
How supplementary plates work
A plate below a sign can narrow it by time (day time, night time), by vehicle class, by distance, or — as here — by conditions. In the test, a question showing two signs stacked is almost always asking whether you read them as one instruction. You should.