Notwithstanding Section 29530 of the Government Code, the Metropolitan Transportation Commission shall, if an unallocated apportionment has been set aside for an operator for specific future expenditures, also set aside annually the interest earned on the unallocated apportionment that has been set aside until the unallocated apportionment is allocated, and shall include the set-aside interest in the amount apportioned to that operator. The interest amount shall be determined by the Metropolitan Transportation Commission based on its estimate of the average rate of interest earned by the unallocated apportionment during the prior fiscal
year.