(a) As used in this section, a "local transportation fund" is a fund created under Section 29530 of the Government Code, or any successor to that statute.

  (b) All local transportation funds are hereby designated trust funds.

  (c) A local transportation fund that has been created pursuant to law may not be abolished.

  (d) Money in a local transportation fund shall be allocated only for the purposes authorized under Article 11 (commencing with Section 29530) of Chapter 2 of Division 3 of Title 3 of the Government Code and Chapter 4 (commencing with Section 99200) of Part 11 of Division 10 of the Public Utilities Code, as those provisions existed on October 1, 1997. Neither the county nor the Legislature may authorize the expenditure of money in a local transportation fund for purposes other than those specified in this subdivision.