I don't think we've done this one yet. In the case of Arizona State Route 260 it would be an Elk. I base this on the fact that there are numerous herds of Elk found on much of AZ 260.
colorado sh-14 = camel
PA 611 - American Bald Eagle
WI 29: Badger (for obvious reasons)
I-90: Buffalo (it goes through two of them)
I-180 WY: Cheetah (with a non-rhotic accent)
MA 2: Make Way for Ducklings
US 201: Moose
Florida's Turnpike: Alligator
US 1 in Maine: Lobster
M-22, VT 100, NC 12: Human
MD 528: Crab
US 83: Cattle (I've never been here; just guessing)
I-695 MD: Oriole
FL 854: Dolphin
ID 33: T-Rex
I-27: Elephant (most Republican Interstate in the country)
I-91: Donkey (pretty Democratic, but there are other contenders)
US 44: Turkey (for Plymouth, MA)
I-99: Cockroach
I-82: Snake (based on curvature)
MX 45: Chihuahua
NJ 495: Sloth
US 2: deer
I-19: scorpion
US 385: antelope
US 101: sea lion