As part of California Vehicle Code Section 40804, any officer whose primary duty is maintaining traffic and enforcing the vehicle code must be in a marked car and in uniform. If the officer in charge of enforcing vehicle code is not in a marked car, their citation will not be valid and they may not be a witness in a trial for any citation they issue while in the unmarked car.
Section 40804 of California vehicle code is sometimes interpreted as meaning that no officers in unmarked cars can issue traffic citations, including speeding offenses. (ref4) This is not true, as officers in unmarked cars can perform this duty as long as their primary law enforcement duty is something other than enforcing the vehicle code.
Hermosa Beach – Unmarked Police Vehicle – What Is The Law ?