Many states have passed laws that require that transgender persons use the bathroom based on their birth gender as shown on their birth certificates, some states permit transgenders to use the bathroom for the sex that they currently associate themselves with, and some states just don't give a crap. (Possibly a poor choice of words, in retrospect.)
Luckily, I was able to interview two of the most famous transgender persons to get their views on the issue. First, I spoke to Chaz Bono, born Chastity Bono. Asked which public bathroom she-he uses, Chaz said that she uses a men's room, but always goes to the privacy of a stall with a door. "I once tried peeing at a urinal, but lacking the necessary physical appendage, the urine just ran down my thighs. It stained my pants, and I got a lot of strange looks from some black guy at the next urinal."
Next, I happened to run into Caitlyn Jenner at a Rexall Drug Store, where he-she was shopping for condoms and sanitary pads. "Caitlyn", I said, "where do you go to pee?" With a deep-throated laugh, the he-she told me that she always uses a woman's room restroom when out in public, since everyone has the privacy of a stall. "At home", he-she continued, "I am just like every other guy. I pee standing up, except at night, when I sit down to pee. In the privacy of my backyard at home, I just raise my dress, pull down my panties, and whip it out. Its habit."