Cal. Veh. Code § 40802
(a) A “speed trap” is either of the following:
(b)
(1) For purposes of this section, a local street or road is one that is functionally classified as “local” on the “California Road System Maps,” that are approved by the Federal Highway Administration and maintained by the Department of Transportation. It may also be defined as a “local street or road” if it primarily provides access to abutting residential property and meets the following three conditions:
(c)
(1) When all of the following criteria are met, paragraph (2) of this subdivision shall be applicable and subdivision (a) shall not be applicable:
(C)
(2) A “speed trap” is either of the following:
(B)
(i) A particular section of a highway or state highway with a prima facie speed limit that is provided by this code or by local ordinance under paragraph (1) of subdivision (b) of Section 22352, or established under Section 22354, 22357, 22358, or 22358.3, if that prima facie speed limit is not justified by an engineering and traffic survey conducted within one of the following time periods, prior to the date of the alleged violation, and enforcement of the speed limit involves the use of radar or any other electronic device that measures the speed of moving objects: