Douglas Harper's Etymology Dictionary
ridership
mid-15c., "position of a rider," from rider + -ship. From 1962 as "number of passengers" (on public transportation, etc.).
Wiktionary
ridership
n. The people who ride a form of transportation.
Usage examples of "ridership".
Twelve carriers left of the fourteen that had come in, a cloud of riderships and dart-ships, bore away from station and into their two outrunners that were distance-blind and alone out there.
The bond payments are to be guaranteed by future revenues from ridership, which is a complete joke.