Cjen1Nerd-sniped on my holiday :)
I saw a stat along the lines of going 2 mph faster than the car in front means you will travel 10m further.
The real question is: How fast would you hit them?
This is what this plot shows.
(60 mph front car, back car at [62, 64, 66, 68] mph reacting 1.5s later, braking at -6.5ms^-2)
