Not sure if this will be on topic but I'd like to know anyway:
Why do mileposts on US Interstates increase South to North instead of North to South?
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I assume the numbering of mileposts is to match the numbering of the U.S. Interstates themselves -- west to east interstates, which have even-numbers, are numbered from south to north (i.e. I-10 runs through southern states, and I-90 runs through northern states). Likewise, south to north interstates, which have odd-numbers, are numbered from west to east -- I-5 runs along the west coast, and I-95 runs along the east coast.
Note that this is the opposite of the US Highway system -- north to south routes grow larger from east to west. US Highway 1 is on the east coast, and the old US Highway 99 (which is now no longer a US Highway) ran along the west coast. Likewise, US Highway 14 runs through several northern states, and US Highway 82 runs across several southern states.
I believe the reason the Interstates were numbered opposite of the US Highways was to avoid confusion, i.e. when talking about route 5 along the west coast, you know the person is talking about an Interstate, not a US Highway.