Cal. Pub. Util. Code § 103350

(a) A retail transactions and use tax ordinance may be adopted by the board in accordance with Part 1.6 (commencing with Section 7251) of Division 2 of the Revenue and Taxation Code and consistent with Article XIII C of the California Constitution.
(b) The board may impose a retail transactions and use tax pursuant to subdivision (a) that, in combination with all taxes imposed in accordance with Part 1.6 (commencing with Section 7251) of Division 2 of the Revenue and Taxation Code, exceeds the limit established in Section 7251.1 of the Revenue and Taxation Code, if both of the following requirements are met:
1. (1) The tax is set at a rate of no more than 0.5 percent.
2. (2) The board adopts the ordinance approving the tax before January 1, 2026.
(c) For purposes of a new tax imposed pursuant to subdivision (b), the board, in concurrence with the County of San Mateo, shall develop an expenditure plan of projects, programs, and services that may include, among other things, public transit, local streets and roads, state highways, bicycle and pedestrian facilities, intelligent transportation systems, and transportation planning.
(d) The board may administer the expenditure plan in its entirety, or may transfer proceeds of the tax to the San Mateo County Transportation Authority for administration by that authority consistent with the expenditure plan.
(e) The board shall not act pursuant to subdivision (b) if a transactions and use tax has been imposed pursuant to Section 7295 of the Revenue and Taxation Code.