@Voland's right hand
"You need 75m braking distance for 70mph. Nobody does that. "
I do actually try and leave a nice safe gap on British motorways - usually without success.
.. Because there.s always some driver who cant resist that stretch of empty space and so has to pull into it.
Only time I get to have a "safe" distance is when MWay is very quiet.
.. I;m a realist (& keen on myself & other road users staying alive) & acknowledge my concentration will not always be 100% when suffering monotonous MWay driving, hence I like a nice safe distance as I expect sub optimal response time if I happen not to be fully focused and so extra reaction time needed.