What does a red traffic signal indicate?

Answer: B — Vehicles must stop

A red traffic signal indicates that vehicles must stop. This signal is a critical component of traffic control systems and plays a vital role in maintaining safety and order at intersections. When a red light is illuminated, it communicates to drivers that they are required to halt their vehicles before the stop line or intersection. This rule applies universally to maintain a standard understanding of traffic signals, ensuring that all road users can predict the actions of others, leading to safer driving conditions. Stopping for a red light allows cross traffic to proceed and provides a safe environment for pedestrians to cross when the signal indicates it is safe to do so. The significance of a red signal is underlined by its visibility and the universal training and regulations surrounding traffic signals that emphasize complete stopping at red lights.