[rootusrootus]

> In Britain at least we call it "braking distance" and you're supposed to leave 2 seconds at least between you and the person in front. Count it off a lamp post/sign etc.

Indeed, that is the usual definition in the US for following distance. Along with a typical example of how to determine it for yourself.

We usually use the term braking distance to describe the distance that would be required to stop the car based on current conditions and speed. This is not necessarily going to be the same as the following distance.

[luxpir]

Thanks for the reply. So then how is following distance determined? It would have to be further than braking distance to be at least as safe?

[rootusrootus]

I do not know how they came up with the 2-4 second following distance recommendation. As you point out, this is in line with what the UK recommends as well. Probably it is a compromise between safety and practicality.

> It would have to be further than braking distance to be at least as safe?

Other way around. Following distance can be less, because the guy you are following cannot stop instantly unless he hits an immovable object or gets into a head-on crash. If he panic stops, then as long as your car performs similarly in braking you just need to have enough distance to allow for your own reaction time.

AFAIK braking distance for most cars is around 5 seconds at highway speed. Few people routinely set their following distance that long.