Interstates? Routes?

If you really want to get into geek-dom, its pretty facinating to actually look at the different number systems.

For example, Interstates are numbered with even numbers on East/West Routes, starting with low numbers in the south and higher numbers in the north. Numbers ending in zero indicate the major cross country route. Odds are the North/South highways, with the major routes ending in the number 5.

US Highways are almost the opposite. East/West Highways end in odd numbers, with lower numbers in the north and higher numbers in the south. North/South routes are odd numbers, starting with route 1 in the East and ending with 101 in the West. One more slight difference from interstate numbering here is that the major routes end in "1" instead of "5"

Each state has their own way of labeling numbers, but they usually aren't quite as formal as the US and Interstate number. Each state also has their own symbols and signs. Some of them look quite close to the US highway shield, and those are the places where you'll often see the signs mis-marked. Thankfully, many states also take care not to double up numbers, so if their is a US-50 in the state, there often won't be a State-50.

And of course I didn't even get into 3-digit highways, which usually indicate an offshoot of a main highway: ie I-290 is a city bypass for I-90.

There are also some cases where the numbering system breaks the mold, but knowing those basic rules can be helpful at times.