How the Interstates got it's numbers
From ggwash.org: Why is I-95 named I-95? What about I-395, or I-270, or I-66? There’s a logical system behind it all, and it's easy to learn. The number of digits tells you whether an interstate connects multiple metro areas, or exists solely within a single metro area. One and two-digit interstates span multiple regions, while three-digit interstates are more local. The rest of the system flows from this most basic starting point. The one/two digit system: There are three factors that go into determining the number for a two-digit interstate: East-west roads get even numbers, while north-south roads get odd. The lowest numbers begin in the south and west, and get higher as you progressively move north and east. The most important cross-country interstates get numbers divisible by five, meaning they end in zero or five. Thus, for example, the name I-95 was reserved for the farthest east major national cross-country interstate that traverses a north-sout...