From the US Customs web pages...
AUTOMOBILES, VEHICLES AND VEHICLE EQUIPMENT
Safety, Bumper, and Emission Requirements. As a general rule, all imported motor vehicles less than 25 years old and items of motor vehicle equipment must comply with all applicable Federal Motor Vehicle Safety Standards in effect when these vehicles or items were manufactured. A Customs inspection at the time of entry will determine such compliance, which is verified by the original manufacturer's certification permanently affixed to the vehicle or merchandise. An entry declaration form, HS-7, must be filed when motor vehicles or items of motor vehicle equipment are entered. The HS-7 can be obtained from customs brokers or ports of entry.
Certain temporary importations may be exempt from the requirements for conformance if written approval is obtained in advance from both the U.S. Department of Transportation and the Environmental Protection Agency. This includes vehicles brought in for research, demonstrations, investigation, studies, testing or competitive events. Also, EPA form 3520-1 and DOT form HS-7 must be submitted to Customs at the time entry is made for such vehicles.
Vehicles imported for temporary use by certain nonresidents or by members of foreign governments or foreign armed forces may not be required to comply with safety, bumper, emission, or theft-prevention standards. Nonconforming vehicles imported by nonresidents for personal use must be exported at the end of one year. Vehicles described in this paragraph may also require EPA and DOT declarations (forms 3520-1 and HS-7, respectively).
A DOT bond in the amount of 150 percent of the vehicle's dutiable value must be posted at the port of entry when a noncertified or nonconforming vehicle is imported for permanent use. The importer must also sign a contract with a DOT-registered importer, who will modify the vehicle to conform with all applicable safety and bumper standards, and who can certify the modification(s). A copy of this contract must be furnished to the Customs Service with the HS-7 at the port of entry. Furthermore, the vehicle model and model year must be determined to be eligible for importation.
For additional information or details on these requirements, contact the U.S. Department of Transportation, National Highway Traffic Safety Administration, Director of the Office of Vehicle Safety Compliance (NEF-32), 400 Seventh Street SW, Washington, DC 20590 Tel. (1-800) 424-9393.
The Clean Air Act, as amended, prohibits the importation of any motor vehicle or motor vehicle engine not in conformity with emission requirements prescribed by the U.S. Environmental Protection Agency (EPA). This restriction applies whether the motor vehicle or motor vehicle engine is new or used, and whether it was originally produced for sale and use in a foreign country or originally produced (or later modified) to conform to EPA requirements for sale or use in the United States. In addition to passenger cars, all trucks, multipurpose vehicles (e.g., all-terrain vehicles, campers), motorcycles, etc., that are capable of being registered by a state for use on public roads or that the EPA has deemed capable of being safely driven on public roads, are subject to these requirements. The term "vehicle" is used below to include all EPA-regulated vehicles and engines.
U.S.-Version Vehicles: Any person may import U.S.-version vehicles. All such 1971 and later models are required to have a label in a readily visible position in the engine compartment stating that the vehicle conforms to U.S. requirements. This label will read "Vehicle Emission Control Information" and will have a statement by the manufacturer that the vehicle meets U.S. EPA emission requirements at the time of manufacture. If this label is not present, the importer should obtain a letter of conformity from the manufacturer's United States representative--not from a dealership--prior to importation.
Non-U.S.-Version Vehicles: Individuals are not permitted to import non-U.S.-version vehicles (unless otherwise excluded or exempted; see next sections). These vehicles must be imported (entered) by an Independent Commercial Importer (ICI) having a currently valid qualifying certificate of conformity for each vehicle being imported. The ICI will be responsible for performing all necessary modifications, testing and labeling, as well as providing an emissions warranty identical to the emissions warranty required of new vehicles sold in the U.S.
A list of approved ICIs is available from the EPA. Vehicles at least 21 years old are exempt from these provisions and may be imported without modification.
WORDS OF CAUTION:
Not all nonconforming vehicles are eligible for importation, and ICIs are not required to accept vehicles for which they have qualifying certificates of conformity.
EPA certification of ICIs does not guarantee the actions or work of the ICIs, nor does it regulate contractual agreements and working relationships with vehicle owners.
EPA strongly recommends that prospective importers buy only U.S.-version (labeled) vehicles, because of the expense and potential difficulties involved with importing a non-U.S.-version vehicle.
EPA strongly recommends that current owners of non-U.S.-version vehicles sell or otherwise dispose of them overseas rather than ship and import them into the U.S., because of the expense and potential difficulties involved with importing a non-U.S.-version vehicle.
Before shipping a nonconforming vehicle for importation, EPA strongly recommends that the importer either make final arrangements with an ICI for modifications and testing or obtain EPA approval in writing for importation. Storage fees at the ports are costly, and the vehicle may not be eligible for importation.
The EPA policy that permitted importers a one-time exemption for vehicles at least five years old has been eliminated.
EPA considers a U.S.-version vehicle that has had modifications to its drive train or emission control system to be a non-U.S.-version vehicle, even though it may be labeled a U.S.-version vehicle.
For Further Information: Environmental Protection Agency, Investigation/Imports Section (6405-J), Washington, DC 20460;
Tel. (202) 564-9660; Fax (202) 565-2057.
Final Word of Caution. Modifications necessary to bring a nonconforming vehicle into conformity with the safety, bumper, or emission standards may require extensive engineering, be impractical or impossible, or the labor and materials may be unduly expensive. It is highly recommended that these modifications be investigated before a vehicle is purchased for importation.
