This Bradley sponsored public service announcement from 1975 talks about some of the longstanding concerns for accessible restroom design.
Thirty six minutes is pretty long for a video if you're just surfing around, but this one might be worth watching if you're involved with restroom design. Just about the most surprising thing about this video is how similar the concerns for accessibility were over 30 years ago. Accessibility and usability for all restroom visitors has always had to be a conscious decision early in the design process, and patrons still have realitively the same needs as they ever have.
Most accessibility design considerations end up benefit to all restroom visitors. Just watching the opening introduction, you can see how a door that opens in a way that doesn't allow a wheelchair into the bathroom, would get in the way of anyone trying to enter or leave the restroom.
Other topics covered in the video that still ring true are the differences of opinions and regulations concerning accessibility. There's a general consensus for the idea of requiring simple activations for fixtures, adequate grab bars, and sufficient clearances. Specifying exact dimensions for these requirements can generate some disagreements though. Because of this, the official requirements can vary from location to location.
Since the making of this PSA, the Americans with Disabilites Act has at least created a national set of standards that everyone can use as a starting point for accessibility requirements. Many local codes actually supersede the ADA in certain situations though, and must be consulted. Often the best procedure is to designing with the best experience for all patrons in mind and then confirming those design decisions with your local codes.
You can do some further reading on the topic with Bradley's Accessibility Design Guide for other considerations for universal accessibility. Always be sure to review the requirements of local codes before committing to a particular layout.