I thought I might chime in on this thread.
Over a year ago, I spent a few weeks playing telephone tag with some folks in DC about this topic, and the wording of the law. The law is currently written with boarding direction in mind for lift buses only. There is no law for ramps just yet, because they are "new" relativly speaking to the transit world.
With that in mind, Disney's policy is such:
Guests boarding the RTS standard floor bus, equipped with a lift may board in the direction of thier choice.
Guests boarding the Nova LFS low-floor bus may board in any direction, if they are using a manual push wheelchair.
If a guest is using any other electric mobility device (electric wheelchair, scooter, ecv, etc), they have the following options:
1.) Board the bus in Reverse.
2.) Step out of such device, and manually drive it in forward(with power is okay) up the ramp. (The key is that no one may be sitting in the device at the time it is going in forward up the ramp.)
3.) Wait for a different style bus.
Curb or no curb makes no difference.
Whether or not this policy is right or wrong, or whether it is too generalized, and not specific to certain types of mobility devices it is Disney policy, and drivers are required to sign a statement agreeing to abide by it. They are subject to disciplinary action if they do not.
I have argued it till I was blue in the face. I even had one of my managers come meet a guest using an electric wheelchair where it was by far better to go in forward. The policy remains, for liability reasons, and drivers do not have a choice in the matter. If a guest has an issue, they should realize that it is out of the drivers control, and they should request to speak to a member of the Disney Transport management team.
Now... here's the GOOD news.
Disney placed an order for 45 Gillig Advantage low-floor buses. About half of them have arrived, and will be entering service soon. The other half will be arriving towards the end of 2005, give or take.
(EDIT: All 45 are currently in service NOW! 
)
The Gilligs will be set up in a similar fashion, 2 positions, with the wheelchair ramp in the rear door. HOWEVER, the ramp is a flip-out style ramp, instead of the unreliable extendable ramp. This is good, because it can be easily operated manually, in the case of mechanical failure.
Because of the modified design of the Gillig, at the time of this writing, guests *WILL* be allowed to board the Gillig low-floor bus in any direction that they choose. (This applies
ONLY to the Gillig, and of course, is subject to change at any given moment without notice)
The reason why it is being allowed in the Gillig and NOT the Nova is that the Gillig was specially modified to reduce the boarding angle. There are also some other technical details that I cannot go into detail with.
As always, if anyone has any questions, please feel free to PM me.
