In case this information helps anyone else dealing with this, I spoke to my attorney at TCTA last year because my district started hassling me to drive, but I have some medical conditions that would prevent me from doing so (also in general I didn't feel safe to drive late nights after sometimes being up for almost 24 hours). They kept coming back and pressuring me about it over and over, even after I told them that I didn't feel that I could safely drive. The TCTA attorney also advised me that "other duties assigned" does not apply to things that are substantially outside the normal duties you would be expected to perform in the course of your job, unless the district had previously made that a condition of my employment, which they had not. So, guess what? They wrote it into our contracts for the following year.

So on the advice of my attorney I had my doctor write a note which I submitted to our HR person. Then they said I had to see their doctor for a physical to verify my personal physician's opinion. I spoke to my attorney again, and he said absolutely not, and that they were going to be in violation of some aspects of the ADA, so I very professionally brought this to my superintendent's attention, and lo & behold they accepted the note from my personal physician (which by the way, due to protecting my privacy, did not have to specify what condition, only that it would prevent me from driving a bus).

So the moral of the story is 1) TCTA is awesome 2) it's great going into a meeting with your principal or super knowing exactly what your legal rights & contractual obligations are and 3) if you do have a medical condition that would preclude you from driving, you shouldn't have to see their doctor or be forced to do testing and/or drive.