Lowered Vehicles
State agencies and legislatures sometimes pursue vehicle height restrictions. A compromise between regulators and modifiers who lower vehicles from the original height can apply the standard of the "scrub line." A scrub line is an imaginary surface created if lines were drawn from the bottom of the wheel rim on one side to the bottom of the tire on the other side. When lines are drawn from both sides using a taut string, an ''X'' under the vehicle's suspension is created. A suspension or chassis component, excepting exhaust systems and sheetmetal, may not be below the top portion of this "X."

Many states choose simply to place limitations on maximum vehicle height. Others prohibit modification of a vehicle in a way that would cause the vehicle body or chassis to come into contact with the ground, expose the fuel tank to damage from collision, or cause the wheels to come in contact with the body.

Street Rod & Custom Vehicle Registration and Titling Process
Special titling and registration designation and recognition of specialty cars including antique, street rod, custom, classic, collector, modified, replica, and kit car vehicles has led to an easing of certain equipment standards and exemptions from stringent emission testing, allowing enthusiasts to enjoy the auto hobby legally and provide more business opportunities to industry. The SAN supports initiatives to establish distinctive license plates and separate vehicle code definitions for these cars to increase awareness and allow special consideration during emission testing and equipment inspections. The SAN also supports initiatives to create classic motor vehicle project titles that apply to vehicles undergoing restoration that are at least 25 years old, not roadworthy, and currently without a title or with a title from another state. Additionally, the SAN also supports initiatives to establish minimal one-time registration fees for specialty vehicles.

So, what exactly are street rods and custom cars and what are the differences between the two? The street rod group is made up of vehicles with body types from manufacture years prior to 1949. Unlike antiques or vehicles found in the restoration niche, street rods have been altered with new equipment and usually take advantage of the many technological advances and upgrades. Street rod builders also commonly use other make or model components to tweak existing parts. Although custom cars are modified with similar materials as street rods, there is a key difference: customs were built from 1949 through the present day. Most of the classic truck market falls into the latter category.

However, beloved street rods and customs (including kit cars and replicas) have long struggled to find their place in the law. Almost all states have processes through which antiques can be registered, but fewer provide adequately for modified cars. Hobbyists attempting to title and register vehicles that they have built from the ground up must often find loopholes in their state's code to get it out on the road. The steps can be so time-consuming and confusing that many throw in the towel.

Summary of the SEMA Street Rod Custom Vehicle Bill
Defines a street rod as an altered vehicle manufactured before 1949 and a custom vehicle as an altered vehicle manufactured after 1948.

Provides specific registration classes and license plates for street rods and custom vehicles.

Provides that replica vehicles and kit cars will be assigned the same model-year designations as the production vehicles they most closely resemble and allows the use of non-original materials.

Exempts street rods and custom vehicles from periodic vehicle inspections and emissions inspections.

Provides that vehicles titled and registered as street rods and custom vehicles may only be used for occasional transportation, exhibitions, club activities, parades, tours, etc. and not for general daily transportation.