Five Car lengths, but only if you are on your toes. It depends on how alert you are at the time and if you can see and monitor the tail lights of the chain gang a lot further ahead than the car in front of you. If you are behind a car and it hits a stopped dump truck - can you stop? If you are tired - give yourself a lot of stopping room.
Actually, 9 car lengths if using 2-second rule. If follow 3-second rule, you should keep 13 car length.
2
1m
3 seconds
Six car lengths is a good distance.
6 feet
600 feet
at least ten feet away.
The driving distance is about 1,620 kilometers. One should be wary of safe driving practice, the change from miles per hour to kilometers per hour, and tolls.
It is a lot easier to count seconds than to estimate distance.
Safe driving is not dangerous driving
One car length per 10 mph
That will depend on the weather, road conditions, the loading in YOUR car and the speed you are driving at. At all times you must make sure that your distance behind the car inform is more than your safe stopping distance.