[hexane360]

And you can tell that it's a loop because it has an even first number.

#: Main Highway ##: Main Highway [Even]##: Loop [Odd]##: Spur

One of the great things about the interstate system.

[madcaptenor]

That's sort of true, but "loop" just means that both ends are at interstates. See for example I-675 south of Atlanta, which runs from I-285 to I-75 in roughly a straight line.