What are the ADA's requirements for public transit buses?

The Department of Transportation has issued regulations mandating accessible public transit vehicles and facilities. The regulations include requirements that all new fixed-route, public transit buses be accessible and that supplementary paratransit services be provided for those individuals with disabilities who cannot use fixed-route bus service.

49 CFR Part 38 – Americans with Disabilities Act Accessibility Specifications for Transportation Vehicles
https://www.law.cornell.edu/cfr/text/49/part-38
49 CFR Part 37-Transportation Services for Individuals with Disabilities (ADA)
https://www.law.cornell.edu/cfr/text/49/part-38