www.r17.me

 

"R is a velocity measure, defined as a reasonable speed of travel that is consistent with health, mental wellbeing and not being more than say five minutes late. It is therefore clearly an almost infinitely variable figure according to circumstances, since the first two factors vary not only with speed taken as an absolute, but also with an awareness of the third factor.

R17 is not a fixed velocity, but it is clearly far too fast."

Douglas Adams, "The Hitch-Hikers Guide to the Galaxy"