A flashing red signal light at an intersection indicates that drivers must:

Answer: D — Stop and proceed only when it is safe to do so.

A flashing red signal light at an intersection operates similarly to a stop sign. It requires drivers to come to a complete stop before proceeding. This means that drivers must first assess the situation to ensure it is safe to move forward. The requirement to stop ensures that all traffic participants, including vehicles and pedestrians, have the opportunity to cross the intersection safely. In this context, stopping at a flashing red light allows drivers to yield the right-of-way to others who may be approaching the intersection, similar to obeying a stop sign. The emphasis on safety means that proceeding only when it is deemed secure is critical to preventing accidents. As for the other options, they do not align with the traffic rules governing flashing red lights. A non-functional signal would not apply if the light is indeed flashing red, indicating a need for caution at the intersection. Yielding right-of-way without stopping is insufficient since the immediate requirement is to halt completely. Additionally, merely slowing down without a complete stop puts other road users at risk, contradicting the safety intent of the flashing red light.