For purposes of this article:
(a) “Commissions” means the county transportation commissions of Los Angeles, Orange, Riverside, and San Bernardino Counties.
(b) “Region” means the multicounty region within the collective jurisdiction of the four commissions.
(c) “Regional transit service” means each existing and planned public transit service, including those which are privately owned and which either receive public funds or are operated under an agreement pursuant to Section 143 of the Streets and Highways Code, whether provided by rail or bus, which operates or is planned for operation between two or more counties within the region.