Understanding the 4-second rule
Previously, drivers were taught that, between your car and the one in front of you, you should maintain a car length of distance for every 10 mph you are traveling. However, most people can’t tell you how long their car is while they are looking at it standing still – much less when it is moving and they are in the driver’s seat. For this reason, the 4-second rule was developed.
The 4-Second Rule
Pick a point on the road. Use a line, sign, pothole, bridge, shadow, etc.
Begin counting. ("One Thousand One, One Thousand Two,” etc.) when the car ahead passes this point. Count slowly and steadily.
If you did NOT reach 4 before the point passed your front bumper, then you are too close to the car ahead. At 55 mph, you should be almost 323 feet behind the car ahead. People complain that it is impossible to maintain this following distance. If you maintain the speed limit, then most cars will be pulling away from you, so it is actually easy to maintain the following distance.
Variation from the 4 Second Rule
Increase following distance to allow for greater stopping distance. When driving in rain or snow, always allow yourself extra room to make any emergency stops.
Following a motorcycle
Motorcycles have much shorter stopping distances than most autos. Motorcyclists have much less protection than drivers of autos.
Increase following distance to prevent the driver behind from being surprised if you have to stop. It also encourages them to pass you. NEVER slam on your brakes to discourage tailgaters.