Standards (or lack thereof)

So, where I work, we have a variety of different school buses.  Newer, older.  Air brakes, hydraulic brakes. One handrail, two handrails.  You get my point. 

For those who don't know, school bus windows have a couple of stops they can be left open at: fully open, half open, and approximately 1" open.  

We have a driver who, because of a reported injury, "can't" use buses with only one handrail on a certain side.  Not quite sure how that driver is able to steer a 40', 15-ton vehicle, but whatever.

This morning, this driver asked for someone to close the windows on the bus, because said driver wasn't able to do it themselves.  These windows were at the 1" mark, but the seats were soaking wet because of the wind and rain.  The way to close the windows from this location is to lower the window, then slide it all the way up.  But apparently, this is beyond the capabilities of this driver.

At what point do we determine that a driver is not physically capable of driving a bus?  When they can't close the windows?  When they can't get into the bus without needing both arms to drag themselves up the stairs?  When they get into a collisions because they don't have the ability to use both arms to turn the steering wheel

What. The. Actual. Fuck?