U.S. Federal law encourages the use of fuel efficient vehicles in a number of ways. The first important concept is that of Corporate Average Fuel Economy (CAFE). Manufacturers are required to meet certain mileage requirements on the vehicles which they manufacture. Separate calculations are made for passenger cars and the manufacturers choice of separate 2WD and 4WD truck categories, or "combined" trucks. Separate calculations are made for domestic (75 percent domestic content) and imported vehicles. These standards, which may be modified by National Highway Traffic Safety Administration, currently are as follows:

Calculation is the same as for "labels" (see below), except that actual production figures are used in place of projected sales. The CAFE is the sales-weighted average of all model types sold.  The final average is adjusted to account for changes to the test procedures since the base year. All tests run for labels or other purposes are included in the calculation At the minimum the manufacturer must conduct sufficient vehicle testing to cover 90 percent of actual sales by configuration. Manufacturers conduct vehicle tests at their laboratories, and the EPA confirms about 30 percent of the vehicles at the EPA lab.

The penalties can be substantial. The fines are calculated at $5 per tenth of mpg above the target for each vehicle produced. The fines are collected by NHTSA which can grant exemptions and alternative standards. Credits can be carried forward or back in time for up to three years to offset fines calculated in other years.

The Gas Mileage Guide is published and distributed by DOE based on EPA's data. Manufacturers are required to label all cars and light trucks (less than 6500 pounds of gross vehicle weight rating (GVWR)) with the fuel economy values on a window sticker. New car dealers are required to have copies of the Guide available. Fuel Economy Guide data is derived from vehicle testing done at the EPA's National Vehicle and Fuel Emissions Laboratory in Ann Arbor, Michigan and by vehicle manufacturers who submit their own test data to EPA. Manufacturers are required to test one vehicle in each base level (combination of inertia weight classes (250 to 500 pound increments), transmission class (manual, automatic), and basic engine (size, cylinders, fuel system). Manufacturers test vehicles at their laboratories, and the EPA confirms about 30 percent of the vehicles submitted. See the Model Year 2000 Fuel Economy Guide Interactive Website

Vehicles are driven over identical driving patterns by professional drivers in controlled laboratory on a dynamometer. Road forces and aerodynamic forces are theoretically accounted for in the test. The city test is 7.5 miles long and is a stop and go trip with an average speed of about 20 miles per hour (mph). The trip lasts 23 minutes and has 18 stops. About 18 percent of the time is spent idling, as if waiting for traffic lights. A short freeway driving segment is included in the test. The engine is initially started after being parked overnight. The highway is a 10 mile trip with an average speed of 48 mph. The vehicle is started "hot" with little idling and no stops. Fuel economy values are calculated from the emissions generated during the tests using a carbon balance equation after measuring the carbon compounds expelled in the exhaust. Calculation techniques and data are available here.

The "label" calculation for combined fuel economy (not adjusted for reality) is used for determining liability for the Gas Guzzler Tax.  The following Tax Schedule is used to determine the amount of the tax, which is collected by the U.S. Internal Revenue Service:

49 CFR ß 580.5(c) requires that a transferor of a motor vehicle provide an odometer disclosure statement which must be "signed by the transferor, including the printed name." Similarly, 49 CFR ß 580.5(f) requires that the transferee must "sign the disclosure statement, print his name, and return a copy to his transferor." In accordance with these provisions, buyers and sellers must hand-print their names in the vicinity of their signatures when completing odometer disclosure statements, with typing not permitted. This hand-printing can be an important part of odometer fraud enforcement cases. Sometimes individuals involved in odometer tampering may use an unnatural signature attempting to defeat later handwriting analysis. The printed name may establish the necessary proof of identity in such cases.

Odometer disclosure requirements for repossessed and seized motor vehicles. Where a vehicle is repossessed by a lending institution or the like, which retains title in satisfaction of a lien, such repossession does not constitute a transfer of ownership. The lending-institution is merely protecting a preexisting interest in the vehicle. In such situations, the lending institution is not required to obtain a disclosure from the registered owner. However, when the lending institution sells the vehicle, it must make the required odometer disclosure statement to its buyer.

In cases of vehicles seized under state law, it is typically impossible to obtain an odometer disclosure statement from the person listed as the registered owner of the vehicle at the time of seizure. However, the inability to obtain this disclosure does not relieve a law enforcement agency that seizes and sells or auctions a motor vehicle of the requirement to make an odometer disclosure. Under these circumstances, where the operation of state law effects a vehicle transfer and excludes the original titleholder from participation in the transaction, the state must be deemed to have placed itself in the position of "transferor,"- within the meaning of NHTSA's regulation. Consequently, the state must provide an odometer disclosure to the buyer at the time of sale.

In both cases of repossession and seizure, sellers may not routinely certify that the odometer reading is not the actual mileage traveled by the vehicle, simply because they cannot attest to its accuracy. The certification portion of the disclosure statement asks the transferor to certify that, to the best of the transferor's knowledge, the odometer reading reflects the actual mileage. If the transferor has no independent reason to believe that the odometer reading is not the actual mileage, the transferor should certify that the odometer reading reflects the actual mileage.