I found this online. It may answer some questions.
CALIFORNIA DEPARTMENT OF TRANSPORTATION (CALTRANS)
TRAFFIC OPERATIONS PROGRAM
OFFICE OF TRUCK SERVICES
Note: This fact sheet is subject to revision. Please revisit this web site for updates.
What is the purpose of this fact sheet? Single-unit vehicles in California, including motorhomes, may be up to 40 feet in length. Single-unit motorhomes that are over 40 feet, up to 45 feet, are legal in California, but only on certain routes. (For simplicity, we refer to these as 45-foot motorhomes.) This fact sheet addresses 45-foot motorhomes. (Note: A vehicle combination, e.g. a motorhome towing a vehicle or trailer, may be up to 65 feet length. If the single-unit motorhome is 40 feet or less in length, the combination is not subject to the 45-foot motorhome restrictions.)The primary purpose of this fact sheet is to enhance communication between Caltrans, the motorhome industry, and motorhome customers regarding legal, engineering, and safety issues.
Are 45-foot motorhomes legal in California? Yes. On October 9, 2001, Governor Davis signed Assembly Bill 67 which legalized motorhomes over 40 feet in length, up to 45 feet, on certain routes, effective immediately.
What is a motorhome? A motorhome is a noncommercial passenger vehicle defined in the California Vehicle Code (CVC) Section 465 as a "house car" and commonly referred to as a recreation vehicle. CVC 362 defines "house car" as "a motor vehicle originally designed, or permanently altered, and equipped for human habitation, or to which a camper has been permanently attached." A motorhome should not to be confused with a bus (CVC 233) or a tour bus (CVC 612), also called "motorcoach," which is used for commercial passenger transportation and requires a commercial driver license to operate. See also Public Utilities Code 5360-5379.5 and 226.
What driver license is required to drive a 45-foot motorhome? AB 67 requires a motorhome endorsement on a noncommercial class B driver license issued by the California Department of Motor Vehicles (DMV).
How do I apply for the noncommercial class B license? Click on this DMV web site for commercial vehicle licensing and scroll down to these three topics: "How to apply for a noncommercial driver license," "Requirements for a Noncommercial Class B driver permit," and "Requirements for a Noncommercial Class B driver license." The driver must pass a written and skills examination (i.e. a driving test), submit a specified medical form, and pay a $34 fee. You may use the DMV booklet Recreational Vehicles & Trailers (DL-648) to prepare for the exam. The booklet is available at the local DMV field offices that test motorhomes. To set up an appointment, or locate a booklet, you may call DMV at 1-800-777-0133.
How long is the license valid? The medical exam must be repeated every two years. The license is valid for approximately five years.
What about out-of-state drivers?Non-residents visiting California may not operate a 45-foot motorhome unless in possession of an out-of-state driver license authorizing the operation of that vehicle. Possible additional requirements are under review; you may read the Vehicle Code on-line (see "California Law" section below) or you may call the California Highway Patrol at (916) 445-1865 to discuss non-resident license requirements.
For more information on service access, see the fact sheet Service Access Routes.
Where can I read AB 67? AB 67 is on the web site of the Legislative Counsel of California at this link: AB 67.
What is the California Vehicle Code? California Law consists of the State Constitution, Statutes, and 29 codes covering various subject areas. Legal requirements for vehicles are included in the California Vehicle Code (CVC).
How did AB 67 change the CVC? AB 67 changed or added the following CVC sections:
Class B driver license.
Class B driver license. House car endorsement -- written exam, driving test, and medical exam.
Nonresident requirements. Endorsement requirements, fees and license expiration date.
35400 ( (10)
Route access. Service access.
Where can I read the CVC? The CVC is on the Internet at this link: CVC - Table of Contents. Scroll down to see the section numbers on the right, and click on the appropriate links.
HISTORY of ROUTE RESTRICTIONS
How was the bus and motorhome route network developed? Federal legislation enacted in 1991 allowed 45-foot buses on the National Network of federally funded highways, primarily the Interstates. In 1995, as a result of an engineering analysis, many additional miles of California State highway opened to 45-foot buses. (See Caltrans’ fact sheet "45-Foot Buses" for more information.)
Why are some state routes restricted? Caltrans has authority to limit certain State routes to certain types of vehicles "on the basis of safety and an engineering analysis," per CVC 35401.5(d). Safety is the primary concern when considering vehicle performance on a route. Larger vehicles need a wider area to maneuver safely. If space is limited, it creates an unacceptable safety hazard for adjacent property, vehicles, and pedestrians, but especially for oncoming traffic. Engineers must take all factors into account, but generally will allow long vehicles only on routes that can accommodate the entire body of the vehicle on all turns without crossing the centerline with any part of the vehicle.
Why would the bus analysis apply to motorhomes? From an engineering standpoint, 45-foot motorhomes have similar turning characteristics to 45-foot buses, especially motorhomes created from tour bus conversions. Therefore, now that AB 67 has became law, 45-foot motorhomes are allowed on the same routes as 45-foot buses.