You are responsible for maintaining a safe following distance — one which provides you with sufficient time to stop in an emergency.
Use a four-second following distance when following under ideal driving conditions — allow more time under adverse conditions.
Calculating safe following distance:
1. The rear of the vehicle ahead has just passed the sign you have decided to use as your marker. Begin counting.
2. Count: One thousand and one, one thousand and two, one thousand and three.
3. Count: One thousand and four (four seconds). If it takes less than four seconds for the front of your vehicle to reach the marker, you are too close. Four seconds is correct. The safety factor is even greater if it takes more than four seconds.
If you are being followed too closely, slow down gradually to give the driver behind you time to react. This can reduce your chances of being struck from behind should you need to stop.