What rule helps estimate total stopping distance under ideal conditions?

The four-second rule is an essential guideline used to estimate total stopping distance under ideal driving conditions. This rule helps drivers maintain a safe following distance by suggesting that a driver should stay at least four seconds behind the vehicle in front. The timing starts when the vehicle ahead passes a stationary object, and the driver should count until they reach the same object. This method accounts for both the reaction time and the braking distance.

By using this rule, drivers can better react to sudden stops or slowdowns by ensuring they have adequate space to safely bring their own vehicle to a halt. The four-second rule is particularly effective because it provides a more conservative estimate of necessary stopping distance, giving drivers enough time to perceive a hazard, decide on a response, and implement that response.

In contrast, the other timing rules mentioned—such as the two-second, three-second, and five-second rules—are either shorter or longer than the optimal duration needed for ideal conditions, making them less applicable for estimating total stopping distance accurately and safely.