Final answer:
A good following distance when driving behind another vehicle is the 3-second rule, which should be adjusted according to driving conditions to ensure sufficient stopping distance.
Step-by-step explanation:
When following another car, a good distance to keep is often referred to as the '3-second rule.' This means you should stay at least three seconds behind the vehicle in front of you at any speed. You can measure this by picking a fixed point that the car in front of you passes, then counting how long it takes for you to reach that same point. However, this distance should be increased in adverse weather conditions or when driving at higher speeds. This is important because it provides sufficient time for you to react and stop if the car in front suddenly brakes. The required stopping distance will depend on several factors including the speed of travel, the road conditions, and the driver's reaction time.