If a solid red arrow is displayed, what does it signify?

Answer: A — Full stop required

A solid red arrow signifies that drivers must come to a full stop and cannot proceed in the direction that the arrow indicates. This is similar to a solid red traffic light, which indicates that vehicles must stop and wait until the signal changes. The purpose of the red arrow is to control traffic and ensure safety at intersections by preventing vehicles from turning or proceeding when it is not safe to do so. This rule is crucial for maintaining order on the roads and preventing accidents, as it communicates a clear directive to drivers about when they may proceed. In contrast, the other responses suggest different actions that are not applicable when a solid red arrow is present.