At highway speeds, how far back is following one car length?

Following one car length at highway speeds is fundamentally about maintaining a safe distance that allows for adequate reaction time. As a general rule, a safe following distance is often measured in seconds rather than car lengths. At highway speeds, it's recommended to maintain a distance that can be covered in approximately 2 to 4 seconds.

When driving at higher speeds, the longer the vehicle takes to stop, the more time and distance a driver needs to react to sudden changes in traffic. Thus, looking at the choices, a following distance of 1/6 of a second would be insufficient for safe driving at highway speeds, as it does not account for the time needed for reaction and braking.

A good rule of thumb is the two-second rule: drivers should ideally allow for two seconds between their vehicle and the vehicle in front of them. This time allows for a margin to assess the road conditions, respond to unexpected stops, and prevent rear-end collisions. Therefore, the more accurate answer that reflects safe driving practices at highway speeds would be measured in seconds much greater than 1/6.