<P> The two - second rule (also known as the three - second rule in some states) is a rule of thumb by which a driver may maintain a safe trailing distance at any speed . The rule is that a driver should ideally stay at least two seconds behind any vehicle that is directly in front of his or her vehicle . It is intended for automobiles, although its general principle applies to other types of vehicles . </P> <P> The two seconds is not a guide to safe stopping distance . It is more a guide to reaction times . </P> <P> The two - second rule is useful as it can be applied to any speed . It is equivalent to one vehicle - length for every 8 km / h (5 mph) of the current speed, but drivers can find it difficult to estimate the correct distance from the car in front, let alone to remember the stopping distances that are required for a given speed, or to compute the linear equation on the fly . The two - second rule gets around these problems, and provides a simple and common - sense way of improving road safety . </P> <P> The practice has been shown to considerably reduce risk of collision, and also the severity of an accident, if an accident occurs . It also helps to avoid tailgating and road rage for all drivers . </P>

What is the safe distance to keep when following another vehicle