Why does the Americans with Disabilities Act (ADA) limit paratransit service to areas where there is already a bus route?

Under the Americans with Disabilities Act (ADA), paratransit functions as a “safety net” for persons whose disabilities prevent them from using the regular fixed route system (bus or rail). It is not intended to meet all of the transportation needs of all persons with disabilities, all of the time. As such, the level of service provided is required to be comparable to that available on the fixed route system; the hours and days of operation must be the same, and service must be provided to origins and destinations within three-fourths of a mile of a bus route (or between points within a three-fourths of a mile radius of different rail stations). There is no obligation to provide service to points beyond the service area, or during times of day or on days of the week when the comparable bus route or rail line is not operating. Of course, nothing in the ADA prohibits a transit system from operating service above and beyond the minimum ADA requirements. It is also important to note that while the term "paratransit" is often used to mean any kind of demand-responsive transportation service, it has a specific meaning under the ADA. The ADA paratransit eligibility criteria and service requirements apply only to paratransit operated as a complement to a fixed route system operated by a public entity; there are separate provisions covering demand-responsive service provided for the general public.