Equipment Standards & Inspections
Understanding how vehicles and car parts are regulated can be a bit confusing. Here is a quick overview.
The Federal government, through the National Highway Traffic Safety Administration (NHTSA), has the right to set, enforce and investigate safety standards for new motor vehicles and motor vehicle equipment. These "Federal Motor Vehicle Safety Standards" (FMVSS) are performance-based. They do not dictate design elements. For example, the federal lighting standard prescribes the photometric requirements for a headlamp but does not dictate shape or size.
The FMVSS covers basic types of equipment (e.g. tires, rims, headlamps/tail lamps, brake hoses, etc.) and establishes vehicle crashworthiness requirements (front and side impact, roof crush resistance, fuel system integrity, etc.).
Emissions and emissions-related parts are regulated by the U.S. Environmental Protection Agency (EPA) and various state agencies, primary of which is the California Air Resources Board (CARB). For products sold in California (and states that have adopted the California standards), manufacturers must conform to standards issued by the CARB.
Federal law prohibits states from issuing motor vehicle safety regulations that conflict with federal standards. This is called federal preemption. However, states are free to enact and enforce safety and equipment regulations which are identical to the FMVSS or, in the absence of a federal rule, establish their own laws and regulations. The most frequent examples of individual state rules cover parts like "optional" or "accessory" lighting equipment, noise levels for exhaust and stereo systems, suspension height and window-tinting. States also establish rules on how a vehicle is titled and registered. State and local jurisdictions have authority to regulate inoperable vehicles or determine whether an enthusiast is engaged in a business vs. private activity. State and local law enforcement officials issue tickets and inspect cars.
State laws have evolved over many generations and they continue to change. Some laws are better than others, and there is a constant need to remind state policy makers not to be biased in favor of the vehicle's original equipment, such as lighting, tires and wheels, suspension components, and bumper/frame height. For example, some state laws allow motorists to be ticketed when an officer has made a subjective noise level determination that the exhaust system is "louder than what came with the car." To cite another example, bills have been introduced in state legislatures to ban spinners even though they are legal at the federal level. Opposing arbitrary and unnecessarily restrictive equipment and inspection laws is a constant challenge.