What do traffic signals indicate for vehicles?

Traffic signals serve a fundamental role in regulating the flow of vehicles and ensuring safety on the roads. When traffic signals are in operation, they manage how vehicles move at intersections and along roadways, which is essential for maintaining an orderly and safe transportation system.

The correct choice highlights that traffic signals facilitate the direct flow of traffic from two different directions, allowing for coordinated movement. This is particularly important at intersections where vehicles need to either yield, proceed, or stop based on the signal's indication. For example, a green light allows vehicles to proceed, while a red light commands them to stop, thereby managing the interactions between opposing traffic flows safely.

In contrast, the other options do not capture the full functionality of traffic signals. The first option suggests that signals only apply to one-directional traffic, which overlooks their role in managing interactions between vehicles traveling in different directions. The third option implies that signals only guide pedestrian movement, neglecting their primary role in regulating vehicular traffic. Lastly, the option regarding parking zones misrepresents the function of traffic signals altogether, as parking zones are typically indicated by signs rather than signals. Therefore, the correct answer reflects the comprehensive role that traffic signals play in directing and managing traffic flows, ensuring safety for all road users.