I was referring to following distance. And yes, three seconds is the "too liberal" version that I was referring to. Once we have automated systems in place, then anybody cutting into a three second gap gets an automatic $xx fine or some type of penalty to discourage them from doing that.
I assure you, that if every driver on the road was a minimum of 4 seconds behind the car in front of them, with mechanisms to enforce that, certain classes of accidents (predominantly rear-ending events, and rapid-swerve events) would be significantly reduced.
The good news is that over the next 3-5 years, a large number of safety automation systems will start to make their way into high-end $50K+ vehicles. The three that I'm super impressed by (having driven in a bunch of vehicles with them) - are Crash Avoidance (your car hits the breaks to prevent it from running into the vehicle in front of you), Lane Control (Your car keeps you in the current lane), and Blind Spot Protection (Your car prevents you from ramming into a car in your blind spot). If, as I strongly suspect, there is a huge drop in car accidents as a result of these three technologies, then we'll start to see them being introduced into the $30K-$50K range over the following 4-6 years, and then, soon thereafter as the technology has been commoditized, the NHTSA will start requiring it. By 2030, all new cars sold in the United States will require those three technologies.
I can only begin to imagine what new technologies will be developed as the march towards self driving cars takes place.