What did the driver fail to do at the red light?

The driver failed to obey the red light, which is a critical rule of traffic safety. "Obey" in this context refers to the requirement to adhere to traffic signals, which is essential for preventing accidents and ensuring smooth traffic flow. When a driver encounters a red light, they are legally and ethically obliged to stop the vehicle, and failing to do so can lead to dangerous situations for themselves and other road users. The emphasis on this answer highlights the importance of understanding and following traffic laws to maintain safety on the road.

The other options, while relevant to driving, do not capture the specific violation associated with a red light. The driver might have followed the traffic flow or checked their surroundings, and signaling is important for indicating intentions, but these actions do not directly address the responsibility to stop when facing a red light. Thus, "obey" specifically pertains to the disregard of the traffic signal that directly impacts road safety.