Here's what I've been told at WDW, which may not be the same at the other parks (if it's not correct, those of you who are CMs, please correct it):
- When someone boards at the exit, the CMs keep a log of the car (each ride car is numbered) they were loaded into, so that they know which ride cars have people with special needs in them.
- Only a certain number of people with special needs who would have to be evacuated are allowed into each attraction at a time (so that they don't exceed the number who can be evacuated in a reasonable amount of time). In some attractions, they might be able to let another special needs party on after the first party gets past the hard to evacuate point.
- There are many cameras inside each attraction so that the CMs can have a look at what is going on. They can also find a particular car by number and know wherre it is.
- If you can't walk and evacuation is necessary, you will have to wait to be evacuated (as was already mentioned, by the fire department).
- At WDW, the rides with steps do allow people who can't climb steps or walk to ride, it just says you will have to wait to be evacuated. Even if a ride breaks down, an evacuation down steps might not be necessary.
- And, as was already mentioned, a lot of stops that people think are ride malfunctions are just temporary stops to let people with special needs on.