What prohibition does this vertical regulatory sign establish?

Question

DentroTest · Accepted Answer

Sign R-300 (“Minimum separation”) prohibits traveling without keeping, from the vehicle ahead of us, a separation equal to or greater than the figure shown in meters on the sign itself or, if no number appears, serves as a generic reminder of the safety distance that must be kept between vehicles. It does not prohibit traveling side by side with other vehicles: this sign does not regulate side-by-side traffic. Nor does it prohibit overtaking: the prohibition of overtaking is specifically signaled by sign R-305, and R-300 even makes an exception for the case where an overtaking maneuver is about to be carried out.

What prohibition does this vertical regulatory sign establish?

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