What is the length of the M25

[Flyboy]

I have thought long and hard for the saddest question about the M25. What is the difference between the total distance of lane 1 traveling clockwise to lane 1 counter-clockwise

[rd14962]

I believe it is 117 miles all the way around, depending on the time of day it could take anywhere between 1 hour and 50 minutes to about 9 hours!!

Hope this helps

Rupert

[rd14962]

Therefore the answer to your question is about the same distance, give or take a few 100 yards for the tunnel/bridge etc.

[sddsddean]

I have just assumed that the M25 is circular (which it isn't) and used rd's figure of a circumference of 117 miles measured along the centre of the centre reserve. Assuming that it is 3 lane motorway the whole way (which it isn't) the carriageway width is 3 x 3.65m (3.65m per lane) and we will assume the centre reserve is 3m wide. This gives a centre line to rumble edge line distance of 12.5 m. The difference in length of each rumble strip, based on these assumptions, is 78.54metres, or about 5 articulated lorry lengths.

[lebesset]

well , the m25 is not a circle or even appoximately so ; it doesn't cross the thames at dartford! that has a different road number
so , at a guess , have a look at the road markers on each side of the river to find the start/finish points , which will give you the official distances , which will be on the outside of the hard shoulder ,one presumes

[JudgeJ]

I would say that you can assume the M25 is circular. I know there is nominally a break at the Dartford Crossing, where it becomes the A282, but for the purposes of this question I think we can assume it is continuous. The deviations from a true circle (which it obviously demonstrates) should not matter because the extra distance caused by deviations in one direction will cancel those in the other. The only problem with the assumptions to be made is that the distance between lane 1 clockwise and lane 1 anti-clockwise is not constant (because the motorway varies in width).

If you are prepared to ignore that problem then the soution is straightforward. The difference in the circumference of any two concentric circles (e.g. lane 1 clockwise and lane 1 anti-clockwise) can be calculated by the formula 2pi multiplied by the distance between circumference of each of the two circles. sddsddean has the calculation spot on. One interesting thing to note is that it does not matter how long the M25 is. This difference will always be the same.