>> Even at 150 km/h, four seconds is still a distance of 167 m - more than 
>> twice the distance at which you can be fined in Germany.
>
> So going substantially faster than any road in the USA allows, you think 
> you can stop your car in 4 seconds?

It's not the time, it's the distance.  As clipka said, leaving a 4 second 
gap when driving 150 km/hr is 167 metres.  Even if the car ahead instantly 
stops dead with no warning you have 167 metres to do something.  Given that 
a modern car can stop from 150 km/hr within 150 metres (and from 100 km/hr 
in 50 metres), allowing for reaction times at worst you're going to bump in 
to them at a low speed.

Of course in reality cars don't just instantly stop for no reason, and this 
is why the UK and German governments only suggest you leave a minimum of 
around half that gap.

> Here's the problem with that: The guy in 5 in front of you needs five 
> seconds to stop and only has four. Now the guy 4 in front of you has only 
> three seconds to stop. And the guy three in front of you has only 2 
> seconds to stop. Etc.

I don't follow your logic here, if you're leaving a 4 second gap to the car 
immediately ahead, you still have a 4 second gap no matter what the people 
are doing ahead of you.

> This is how you get 300 car pile-ups.

You get 300 car pile-ups because people drive closer (in distance) to the 
car ahead than they need to stop *and* don't pay attention to anything ahead 
of the car immediately in front.  If they fixed either of those two issues 
there wouldn't be any pile up.

> But yeah, if you're going that fast, it's a lot of distance. Just don't 
> get distracted for a second.

The key point is to be aware what is happening far enough ahead of you 
relative to your speed.  Doing 200 km/hr can be safe if you check far enough 
ahead of you that it is clear (not just the one car ahead of you).  If you 
can't for whatever reason then you need to slow down until you can see far 
enough for your speed.

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