Regulatory references: 28 CFR 35.151.
All facilities designed, constructed, or altered by, on behalf of, or for the use of a public entity must be readily accessible and usable by individuals with disabilities, if the construction or alteration is begun after January 26, 1992.
What is "readily accessible and usable?" This means that the facility must be designed, constructed, or altered in strict compliance with a design standard. The regulation gives a choice of two standards that may be used (see II-6.2000).