California Code, Vehicle Code - VEH § 21655.1

(a) A person shall not operate a motor vehicle on a portion of a highway that has been designated for the exclusive use of public transit buses, except in compliance with the directions of a peace officer or official traffic control device.

(b) This section does not apply to a driver who is required to enter a lane designated for the exclusive use of public transit buses in order to make a right turn or a left turn in a location where there is no left-turn lane for motorists, or who is entering into or exiting from a highway, unless there are signs prohibiting turns across the lane or the lane is delineated by a physical separation, including, but not limited to, a curb, fence, landscaping, or other barrier.

(c) A public transit agency, with the agreement of the agency with jurisdiction over the highway, shall place and maintain, or cause to be placed and maintained, signs and other official traffic control devices, as necessary, indicating that a portion of a highway is designated for the exclusive use of public transit buses and to advise motorists of the hours of operation of the lane as an exclusive public transit bus lane.