When driving at highway speeds, how many seconds back do you need to follow to ensure enough room to stop in an emergency?

Answer: C — 4 seconds

When driving at highway speeds, maintaining a following distance of 4 seconds is recommended to ensure enough room to stop in an emergency situation. This guideline is based on the perception-reaction time of drivers, which can take about 1.5 to 2 seconds, and the necessary braking distance, which increases significantly at higher speeds. By allowing for a 4-second gap, drivers have a better opportunity to react to sudden stops or hazards. This distance provides a buffer for various factors such as weather conditions, road surface, and vehicle load, all of which can affect stopping distances. The 4-second rule is widely accepted for safe driving practices on highways, giving you the time to react and brake effectively in case of an emergency.