If Chicago is 53 miles away according to a green sign, where will I be 53 miles from now?
I've often asked myself this (especially during summer months of nomadic existance), but I didn't go looking for answers until an email asking the same question arrived in my inbox.
I started by trying to find out about highway signs in general. A collection of highway signs past and present (also near and far) lead me to a directory of all things streetwise by the same author.
From this directory, I exited onto a Manual of Traffic Signs run by a member of the National Committee on Uniform Traffic Control Devices who is a professional traffic engineer in his spare time (or is it the other way around?). While this site had lovely graphical examples of distance and mileage signs, it didn't explain the whys and wherefores (which are actually the same thing) of how the distances were measured.
So be it. I turned to the latest version of the the Manual on Uniform Traffic Control Devices, because the government, no matter what you may say and feel about its operation, likes to document minutiae in great, if cryptographic, detail. This case was no different.
Section 2E* of the Manual on Uniform Traffic Control Devices, subsection 36 (Distance Signs) reads in part:
The distances displayed on these signs should be the actual distance to the destination points and not to the exit from the freeway or expressway.
That is fascinating, wonderful information and rules out one possibility: distances are not to freeway exits. However, for a final, honest to goodness, salt of the earth explanation, we need to visit the midwest.
The mileage shown on distance signs, reads an Iowa Department of Transportation FAQ, is the distance to a point near the center of the community. A public building such as a post office, city hall or courthouse is used as a point of reference for the center of the community. The mileage is rounded to the nearest mile.
And that is the end of that.
* It's a PDF file, Leadfoot.
Thursday, May 16th, 2002
permanent url
