These signs oblige you to keep distance from the car in front

Explanation

You must keep a distance of more than 70 metres, and this requirement continues for 900 metres.

The round sign with a red border showing two vehicles one behind the other and the figure "70 m" is the "minimum distance" sign: travelling at a distance less than the figure shown is prohibited. So the figure 70 is a floor for the distance, not a ceiling; if you keep 150 metres you have committed no offence. The plate beneath the sign, with two arrows and the figure "900 m", states the length of the zone in which this requirement applies.

This combination is usually posted on bridges, in tunnels and on long descents, and it has two safety reasons. The first is load: a tightly packed queue of vehicles on one bridge span imposes a large concentrated weight on the structure, and a compulsory gap spreads that weight. The second is the chain reaction: in a tunnel or on a descent, one vehicle's emergency braking ends in a multiple collision, and 70 metres means each driver has time to see and stop.

The point to memorise for the exam is that the two figures have entirely different roles: the figure inside the circle is a condition of travel, and the figure on the plate is the length of the territory in which that condition applies. Any option that swaps the two, or treats "less than 70" as the requirement, is the wrong answer.

• It inverts the sign's meaning: the sign prohibits a distance of less than 70 metres, so "less than 70 metres" is exactly what you are not allowed. • It reads the 900-metre plate as "the distance to the start of the restriction", whereas the plate's double-headed arrows show the length of the zone itself and the requirement is in force from here.

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