What is primarily measured by following distance?

Following distance primarily measures reaction time. When driving, maintaining an appropriate following distance allows a driver to better assess the speed of the vehicle ahead and react appropriately to any sudden changes, such as abrupt stops or obstacles in the road.

By keeping a safe distance, drivers have more time to process their surroundings and their own responses, which is critical in avoiding rear-end collisions. It reflects a driver's ability to judge how much space is needed to ensure a safe stop in response to the actions of the vehicle ahead. A longer following distance provides more time to react, particularly in high-speed situations or when driving in less-than-ideal conditions.

The other factors mentioned, like speed, control, and road conditions, can influence safe driving but are not the primary focus of following distance. Following distance is specifically aimed at enabling proper reaction time, which is crucial for the safety of all road users.