Final answer:
The three-second rule is the standard for measuring a safe following distance under normal conditions, ensuring adequate time for reacting to sudden stops.
Step-by-step explanation:
Following other vehicles requires a safe following distance to allow for adequate reaction time in case the vehicle in front stops suddenly. Under normal conditions, a widely-accepted approach is to use the three-second rule for measuring safe following distance. This rule entails observing when the rear end of the vehicle ahead passes a fixed point, such as a sign or a tree, and then counting 'one thousand one, one thousand two, one thousand three'. If you reach the same point before you finish counting, you are following too closely.
To put this into perspective with the scenarios provided, let's consider Bridget's observation from her classroom window. If a car covers 50 meters in 3 seconds, it's adhering roughly to the three-second rule given a certain speed. This rule translates into different normal driving distances depending on the speed of the vehicles. Additionally, the stopping distance of a car involves factors such as reaction time and road conditions, so it's important to maintain a safe following distance beyond the calculated stopping distances to account for various uncertainties on the road.