California Code, Public Utilities Code - PUC § 100605

(a) Special benefit assessments for the payment of the principal of, and interest on, bonds issued for a benefit district or zone shall be levied in the benefit district or zone at rates that are sufficient in the aggregate, together with revenues already collected and available, to pay the principal of, and interest on, all bonds the VTA issued for the benefit district or zone.  Other revenues of the VTA shall be used for the payment of the principal of, and interest on, the bonds only to the extent set forth in any agreement of the VTA for the benefit of bondholders.

(b) Special benefit assessments in the benefit district and zones, if any, therein shall be calculated in accordance with the requirements set forth in Section 4 of Article XIII D of the California Constitution.