Not less than 75 percent of the unallocated apportionment, as of June 30, 1978, and each June 30th thereafter, for the cities, and that portion of the County of San Diego, under the jurisdiction of the San Diego Metropolitan Transit Development Board shall be available to the board for exclusive public mass transit guideway purposes as specified in Article 4 (commencing with Section 120260) of Chapter 4 of Division 11.

On July 1 of the first fiscal year of implementation of Section 120265, this section shall no longer be effective except as to the prior year’s unallocated apportionment.