Safe driving guidelines advise drivers to keep a safe distance between themselves and the car ahead. Drivers need enough time to react if that car makes a sudden turn or stop. It can be too difficult to estimate the recommended distances while driving and the exact distance would have to be adjusted for speed, so most experts recommend a "three-second rule."
The three-second rule is simple. Find a stationary object on the side of the road. When the car ahead of you passes it, start counting seconds. At least three seconds should pass before your car passes the same object [source: SmartMotorist]. Once you have some driving experience and have practiced keeping this minimum distance, you'll develop an instinct for it and know how close to follow without having to count. However, even experienced drivers should count off the three-second rule now and then to make sure.
At night or in inclement weather, double the recommended time to six seconds.