It's a nice thought, but it has so many modifiers it's pretty much worthless. Everything from road conditions, to time of day or night, to the size and weight and type of vehicle you are driving, to how old you are affects stopping distance and the interval you should be leaving.
Remember children - Driving should never be "relaxing." It's real work and demands your total concentration to protect yourself and everyone around you. So put the phone down and even turn off the radio. Put your head on a swivel like a fighter pilot. And have an escape plan for every inch you drive.
I don't know why you are being downvoted since the distance from other cars should absolutely reflect the current conditions. I also agree that to drivers need to proactively look for possible collisions in mirrors and blind spots, though they should be generally calm and patient when driving.