Federal Aviation Administration Draft Advisory Circular 150/5360-14A, Access to Airports by Individuals with Disabilities

1.6.10 Fixed Route System.
A system of transporting individuals (other than by aircraft), including the provision of designated public transportation service by public entities and the provision of transportation service by private entities, including, but not limited to, specified public transportation service, on which a vehicle is operated along a prescribed route according to a fixed schedule. (49 CFR § 37.3).