We’re all familiar with it being further round the outside of a bend than the inside – hence Strava lines, and running tracks with staggered starts. But exactly how much further is it then around the ‘M25’ (nws nickc above) if you were in the left hand lane going clockwise compared to the LH lane going anti-cw?
Must be miles, eh? Nope. Less than 200 metres
Approximate to a circle, with circumference C = pi x D where D = diam of the M25
But, assume that’s the inside diameter, now assume the outside is 8 x 3m lanes and a central reservation wider. Call it 30m but that’s per radius, at both ends = 60m.
So, distance round outside = pi x (D+60) = pi x D + pi x 60. Leaving a difference of only pi x 60 = 188m. 6s longer at a continuous 70mph.
And that’s probably overstated, lanes are typically 2.8m I read somewhere, there aren’t always 8 lanes and the central reservation isn’t 6m.
Bear that in mind if you have to join and exit at opposite sides, a wise choice could save you 2-3 seconds.