[iggldiggl]

> You should be able to safely not rear end the car in front of you even if it immediately hits a brick wall and stops completely, […]

I don't think that's the usual expectation. Maintaining absolute braking distance is what railways do, whereas cars commonly operate on relative braking distance plus a safety margin accounting for your reaction time.

Over here, both driving schools and other general road safety education talk about keeping 2 seconds following distance (or half your kph-speed in metres, which corresponds to 1.8 seconds following distance), and traffic engineers commonly give the capacity of a single lane of traffic as 1800 vehicles/hour, which again corresponds to 2 seconds distance (this time as measured vehicle front to vehicle front, instead of tail to front of following vehicle).