Increasing the distance between you and the car ahead can help give you the time you need to recognize a hazard and respond safely. The National Safety Council recommends a minimum three-second following distance.
Determining the three-second gap is relatively easy. When following a vehicle, pick an overhead road sign, a tree or other roadside marker. Note when the vehicle ahead passes that marker, then see how many seconds it takes (count 1-1,000; 2-1,000; 3-1,000) for you to pass the same spot. If it is not at least three seconds, leave more space and increase your following distance.
Think of following distance in terms of time, not space. With a standard of 2.5 seconds, highway engineers use time, rather than distance, to represent how long it takes a driver to perceive and react to hazards. The National Safety Council also uses this standard (plus a little extra for safety) when recommending the three-second rule for following distance.