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
49 CFR Part 37-Transportation Services for Individuals with Disabilities (ADA)
For additional information, take a look at the following resources: