Which of these signs applies only to the lane above which it is mounted?

Explanation

Only sign Ա — the one beneath which the "lane" supplementary plate with a broad downward arrow is fitted.

A sign mounted overhead on a gantry applies by default to the whole carriageway in that direction. What limits a sign's effect to one particular lane is not the main sign itself; it is the supplementary plate beneath it. In the picture, only beneath Ա is there a white supplementary plate with a broad black arrow pointing down; that is the "lane" plate and it says the 50 restriction applies only to the lane directly above which the sign is placed.

The other two signs have no such companion: Բ is a solid blue circle with the figure 50, meaning "minimum speed", and Գ is a blue square with the figure 50, meaning "recommended speed". Both are without a supplementary plate and their effect spreads across the whole carriageway, not one lane.

The safety reason for this distinction is clear: on multi-lane roads sometimes only one lane has special conditions — a lane approaching a curve or a ramp, or one alongside which repair work is under way. If the restriction on that one lane extended to all lanes, drivers in the other lanes would brake for no reason and a speed difference between lanes would be created; the very thing that produces rear-end impacts and sudden lane changes.

The rule to memorise: the shape and colour of the sign say "what", the supplementary plate beneath it says "where". The exam trap is that all three signs carry the figure 50 and the candidate goes to the blue circle; whereas the criterion for choosing is the downward arrow.

• Բ is the blue "minimum speed" circle and there is no supplementary plate beneath it; having no lane marking, its effect is on the whole carriageway, not one lane. • Both signs are round and carry the figure 50, and that very similarity is tempting, but only Ա has the "lane" plate; Բ lacks it and cannot be confined to one lane.

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