Cal. Sts. & Hy. Code § 2552
When the Metropolitan Transportation Commission or the Sacramento Area Council of Governments functions as the service authority for two or more counties, the revenues which it receives pursuant to Section 9250.10 of the Vehicle Code, after retention of amounts necessary to reimburse the commission or the council for its reasonable and necessary administrative costs, shall be expended for implementation, maintenance, and operation of a motorist aid system within those counties. The amount expended for each of those counties shall be in the same proportion as the revenues generated within the county bears to the total revenues received by the commission or the council. Expenditures may be made in a county in addition to revenues proportionately generated if the expenditures are approved by all of the donor county representatives on the service authority.
Ca. Sts. and High. Code § 2552