Does the Americans with Disabilities Act (ADA) limit subscription trips to 50% of available paratransit trips?

Under Department of Transportation (DOT) Americans with Disabilities Act (ADA) regulations at 49 C.F.R. Section 37.131(b), paratransit service must be provided to eligible individuals on a next-day basis (i.e., at any time tomorrow in response to a request made today). Section 37.133 permits the use of subscription service (i.e., trips provided to eligible ADA paratransit riders who make trips on a repeated or recurring basis, such as to school, work, religious services, dialysis treatment, etc.), as long as it does not absorb more than 50% of the available trips at a given time of day. Section 37.133(b) permits a transit operator to provide subscription service above the 50% ceiling if it finds it has excess capacity available (i.e., all requests for next-day service are met, and capacity to provide additional trips remains). If, after constant monitoring, it finds next-day requestors are being denied trips, the operator must either increase its passenger carrying capacity or reduce the number of subscription trips. Note that subscription service is discretionary and is not mandated by Section 37.133. Whether to provide subscription service beyond the 50% ceiling, or whether to provide subscription service at all, is entirely within the transit agency's discretion.