What must you do when traffic control lights are not functioning at an intersection?

When traffic control lights are not functioning at an intersection, the appropriate response is to come to a full stop. This action is essential because non-functioning traffic lights can create confusion and increase the potential for accidents, as vehicles may approach the intersection without a clear understanding of who has the right of way. By stopping, drivers can assess the situation, check for other vehicles and pedestrians, and determine how to proceed safely through the intersection.

This approach aligns with the principle of caution and defensive driving, ensuring that all road users can react appropriately to the absence of signals. After coming to a full stop, drivers should treat the intersection as a four-way stop, allowing vehicles that arrived first to proceed before them, which helps maintain order and safety in the absence of functioning traffic signals.