Currently they teach 2 to 3 seconds separation.  This is much easier to
judge on the road and takes into account variations in speed.
As a side note on this Washington State, a couple of months ago, tried this
trick to 'help' drivers.  On a section of I-5 that is heavily traveled they
put big white dots on the road as separation markers.  Two marks between
cars at 60 mph.  Worked fine for a couple of days, then heavy weekend
traffic came along.  As traffic slowed down drivers still tried to keep two
dots apart.  Caused an awful backup that day.  The dots were gone a couple
of days later.

On 10/16/06, Jake de Villiers <crescentbeachguitar@gmail.com> wrote:
>
> I believe it was one car length for every ten miles an hour.
> Can be difficult in major urban areas!
>
>