CA Veh Code § 21655.5 (2021)
2021 California Code|Vehicle Code - VEH|DIVISION 11 - RULES OF THE ROAD|CHAPTER 3 - Driving, Overtaking, and Passing|ARTICLE 1 - Driving on Right Side|Section 21655.5.

21655.5.  (a) The Department of Transportation and local authorities, with respect to highways under their respective jurisdictions, may authorize or permit exclusive or preferential use of highway lanes for high-occupancy vehicles. Prior to establishing the lanes, competent engineering estimates shall be made of the effect of the lanes on safety, congestion, and highway capacity.(b) The Department of Transportation and local authorities, with respect to highways under their respective jurisdictions, shall place and maintain, or cause to be placed and maintained, signs and other official traffic control devices to designate the exclusive or preferential lanes, to advise motorists of the applicable vehicle occupancy levels, and, except where ramp metering and bypass lanes are regulated with the activation of traffic signals, to advise motorists of the hours of high-occupancy vehicle usage. A person shall not drive a vehicle upon those lanes except in conformity with the instructions imparted by the official traffic control devices. A motorcycle, a mass transit vehicle, a blood transport vehicle that is clearly and identifiably marked as such on all sides of the vehicle, or a paratransit vehicle that is clearly and identifiably marked on all sides of the vehicle with the name of the paratransit provider may be operated upon those exclusive or preferential use lanes unless specifically prohibited by a traffic control device.(c) When responding to an existing emergency or breakdown in which a mass transit vehicle is blocking an exclusive or preferential use lane, a clearly marked mass transit vehicle, mass transit supervisor’s vehicle, or mass transit maintenance vehicle that is responding to the emergency or breakdown may be operated in the segment of the exclusive or preferential use lane being blocked by the mass transit vehicle, regardless of the number of persons in the vehicle responding to the emergency or breakdown, if both vehicles are owned or operated by the same agency, and that agency provides public mass transit services.(d) For purposes of this section, the following definitions apply:(1) “Blood transport vehicle” means a vehicle owned and operated by the American Red Cross or a blood bank that is transporting blood between collection points and hospitals or storage centers.(2) “Mass transit vehicle” means a transit bus regularly used to transport paying passengers in mass transit service.(3) “Paratransit vehicle” as defined in Section 462.(e) It is the intent of the Legislature, in amending this section, to stimulate and encourage the development of ways and means of relieving traffic congestion on California highways and, at the same time, to encourage individual citizens to pool their vehicular resources and thereby conserve fuel and lessen emission of air pollutants.(f) The provisions of this section regarding mass transit vehicles and paratransit vehicles shall only apply if the Director of Transportation determines that the application will not subject the state to a reduction in the amount of federal aid for highways.(g) The authority for a blood transport vehicle to use exclusive or preferential lanes in accordance with subdivision (b) shall only be operative under either of the following circumstances:(1) The Director of Transportation determines that the use of those lanes by those vehicles will not cause a reduction of federal aid funds for highways or otherwise be inconsistent with federal law or regulations, or with any agreement between the state and a federal agency or department, and the director posts that determination on the Department of Transportation’s Internet Web site.(2) The Federal Highway Administration of the United States Department of Transportation, upon the request of the director, makes that determination and the director posts the determination on the Department of Transportation’s Internet Web site.(Amended by Stats. 2017, Ch. 392, Sec. 2. (SB 406) Effective January 1, 2018.)