What is the minimum safe following distance in seconds for a 40-foot vehicle traveling at 35 mph under good conditions?

The correct answer is based on the principle that maintaining a minimum safe following distance is crucial for ensuring adequate reaction time and preventing collisions. For a vehicle that is 40 feet long traveling at 35 mph under good conditions, the recommended minimum following distance is indeed 4 seconds.

This 4-second rule allows the driver enough time to respond to unexpected events, such as sudden stops by the vehicle ahead. The formula often used for determining this distance is that for every 10 mph of speed, you should allow one second of following distance. Since 35 mph falls between the 30 and 40 mph marks, rounding to 4 seconds provides a buffer that covers not just the speed but also the length of the vehicle, which influences stopping distance.

The length of the vehicle is also relevant; larger vehicles typically require more distance to stop safely compared to smaller vehicles. Therefore, considering both the speed and the vehicle size, 4 seconds is a safe minimum to avoid rear-end collisions and allow for proper reaction time.