Normally, the distance from you to the vehicle ahead should he at least equivalent to:
1. The distance from you to the vehicle ahead should be at least equivalent to the stopping distance at your current speed.
2. The distance from you to the vehicle ahead should be at least equivalent to three seconds of following time.
3. The distance from you to the vehicle ahead should be at least equivalent to the length of two vehicles.
4. The distance from you to the vehicle ahead should be at least equivalent to the length of a city block.