Which of the following signs prohibits traffic with a smaller space than the one shown on the sign?

Explanation

Sign number 3 — the minimum distance sign, 70 metres.

Sign 3 shows two vehicles one behind the other with the figure 70 m above them; it means that entering this section of road at a longitudinal distance of less than 70 metres from the vehicle in front is prohibited. This sign speaks about "the distance between two vehicles", not about the dimensions of the vehicle itself; and that distinction is the whole question.

Such a restriction is usually posted on bridges, in tunnels, on structures of limited load capacity and on long mountain descents. It has two safety reasons: first, reducing the simultaneous load on a single span of the structure, and second, guaranteeing braking distance where a sudden halt of the queue ends in chain collisions. On a descent, a heavy vehicle's braking distance is several times the normal, and a short gap means a certain impact.

For quick recognition in the exam, separate the families of signs: signs that limit one dimension of the vehicle itself with facing arrows (width, height, length) versus the sign that depicts two separate vehicles. Wherever you see two vehicles on a sign, it is about distance.

• Sign 1, with facing arrows and the figure 2.7 m, limits the permitted width of the vehicle; it has nothing to do with the gap between vehicles. • Sign 2, with a lorry and the figure 10 m, limits the length of the vehicle; again one dimension of the vehicle itself, not a distance. • Sign 4 is a supplementary plate showing the length of the zone in which the main sign applies; on its own it creates no prohibition. • Sign 5 is a blue square with the figure 50, that is a recommended speed; its nature is informative and it creates no prohibition at all.

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