Veh. Code, § 35110

(a) Door handles, hinges, cable cinchers, chain binders, aerodynamic devices, holders for the display of placards warning of hazardous materials, and a tarping system and all nonproperty carrying devices or components thereof, may extend three inches on each side of the vehicle.

(b) For purposes of this section, “aerodynamic device” means a device that uses technologies that minimize drag and improve airflow over an entire tractor-trailer vehicle. These include gap fairings that reduce turbulence between the tractor and trailer, side skirts that minimize wind under the trailer, and rear fairings that reduce turbulence and pressure drop at the rear of the trailer, provided that these devices shall not adversely impact the vehicle’s swept width and turning characteristics and that the primary purpose of the device is not for advertising.

(c) (1) For purposes of this section, “a tarping system” means a movable device used to enclose the cargo area of flatbed semitrailers or trailers.

(2) Subdivision (a) applies to all component parts of a tarping system, including the following:

(A) The transverse structure at the front of the vehicle to which the sliding walls and roof of the tarp mechanism are attached, provided the structure is not also intended or designed to comply with Section 393.106 of Title 49 of the Code of Federal Regulations. The transverse structure may be up to 108 inches wide if properly centered so that neither side extends more than three inches beyond the structural edge of the vehicle.

(B) The side rails running the length of the vehicle.

(C) The rear doors, provided the only function of the rear doors is to seal the cargo area and anchor the sliding walls and roof.

(D) The “wings” designed to close the gap between a headerboard designed to comply with Section 393.106 of Title 49 of the Code of Federal Regulations and the movable walls and roof of a tarping system, provided they are add-on pieces designed to bear only the load of the tarping system itself and are not integral parts of the load-bearing headerboard structure.

(d) For purposes of this section, a “headerboard designed to comply with Section 393.106 of Title 49 of the Code of Federal Regulations” is load bearing and does not exceed 102 inches in width.