Miles per gallon gasoline equivalent

Miles per gallon gasoline equivalent is a measure of the average distance traveled per unit of energy consumed. MPGe is used by the United States Environmental Protection Agency to compare energy consumption of alternative fuel vehicles, plug-in electric vehicles and other advanced technology vehicles with the energy consumption of conventional internal combustion vehicles rated in miles per U.S. gallon.
The unit of energy consumed is deemed to be 33.7 kilowatt-hours without regard to the efficiency of conversion of heat energy into electrical energy, also measured in kilowatt-hours.
MPGe does not necessarily represent an equivalency in the operating costs between alternative fuel vehicles and the MPG rating of internal combustion engine vehicles due to the wide variation in costs for the fuel sources regionally since the EPA assumes prices that represents the national averages. Miles per gallon equivalent cost for alternate fuel can be calculated with a simple conversion to the conventional mpg. See conversion to MPG by cost below.
The MPGe metric was introduced in November 2010 by EPA in the Monroney sticker of the Nissan Leaf electric car and the Chevrolet Volt plug-in hybrid. The ratings are based on EPA's formula, in which of electricity is equivalent to one gallon of gasoline, and the energy consumption of each vehicle during EPA's five standard drive cycle tests simulating varying driving conditions. All new cars and light-duty trucks sold in the U.S. are required to have this label showing the EPA's estimate of fuel economy of the vehicle.
In a joint ruling issued in May 2011 the National Highway Traffic Safety Administration and EPA established the new requirements for a fuel economy and environment label that is mandatory for all new passenger cars and trucks starting with model year 2013. This ruling uses miles per gallon gasoline equivalent for all fuel and advanced technology vehicles available in the U.S. market including plug-in hybrids, electric vehicles, flexible-fuel vehicles, hydrogen fuel cell vehicle, natural gas vehicles, diesel-powered vehicles, and gasoline-powered vehicles. In addition to being displayed on new vehicles, fuel economy ratings are used by the U.S. Department of Energy to publish the annual Fuel Economy Guide; the U.S. Department of Transportation to administer the Corporate Average Fuel Economy program; and the Internal Revenue Service to collect gas guzzler taxes.
Fuel economy estimates for window stickers and CAFE standard compliance are different. The EPA MPGe rating shown in the Monroney label is based on the consumption of the on-board energy content stored in the fuel tank or in the vehicle's battery, or any other energy source, and only represents the tank-to-wheel energy consumption. CAFE estimates are based on a well-to-wheel basis and in the case of liquid fuels and electric drive vehicles also account for the energy consumed upstream to produce the fuel or electricity and deliver it to the vehicle. Fuel economy for CAFE purposes include an incentive adjustment for alternative fuel vehicles and plug-in electric vehicles which results in higher MPGe than those estimated for window stickers.

Background

1988: Alternative Motor Fuels Act

The Alternative Motor Fuels Act enacted in 1988 provides Corporate Average Fuel Economy incentives for manufacturing alternative fuel vehicles that are powered by ethanol, methanol, or natural gas fuels, either exclusively or in conjunction with gasoline or diesel fuel. These dual-fuel vehicles also are known as flexible-fuel vehicles. To provide incentives for the widespread use of these fuels and to promote the production of AFVs and FFVs, AMFA grants AFV/FFV manufacturers CAFE credits, which allows them to raise their overall fleet fuel economy levels to comply with the CAFE standards.
Beginning in 1993, manufacturers of qualified AFVs can improve their CAFE estimation by computing the weighted average of the fuel economy when operating on conventional fuel and when operating on alternative fuel. AMFA provides the following energy content-based equivalency factors:

1 gal = 0.15 gal
100 ft³ = 0.823 gal-equivalent
* 1 gal-equivalent = 0.15 gal

A dedicated AFV which operates solely on alcohol would divide the alcohol fuel economy by the energy-equivalency factor of 0.15. As an example, a dedicated AFV that achieves 15 mpg fuel economy while operating on alcohol would have a CAFE calculated as follows:
For FFVs, an assumption is made that the vehicles would operate 50% of the time on the alternative fuel and 50% of the time on conventional fuel, resulting in a fuel economy that is based on a harmonic average of alternative fuel and conventional fuel. For example, for an alternative dual-fuel model that achieves 15 miles per gallon operating on an alcohol fuel and 25 mpg on the conventional fuel, the resulting CAFE would be:
Calculation of fuel economy for natural gas vehicles is similar. For the purposes of this calculation, the fuel economy is equal to the weighted average of the fuel economy while operating on natural gas and while operating on either gasoline or diesel fuel. AMFA specifies the energy content of 100 cubic feet of natural gas to be equal to 0.823 gallons-equivalent of natural gas, and the gallon equivalency of natural gas is considered to have a fuel content, similar to that for alcohol fuels, equal to 0.15 gallons of fuel. For example, under this conversion and gallon equivalency, a dedicated natural gas vehicle that achieves 25 miles per 100 cubic feet of natural gas would have a CAFE value as follows:
The Energy Policy Act of 1992 expanded the definition of alternative fuel to include liquefied petroleum gas, hydrogen, liquid fuels derived from coal and biological materials, electricity and any other fuel that the Secretary of Transportation determines to be substantially non-petroleum based and has environmental and energy security benefits. Beginning in 1993, manufacturers of these other alternative fuel automobiles that meet the qualifying requirements can also benefit for special treatment in the calculation of their CAFE.

1994: Gasoline gallon equivalent

In 1994 the U.S. National Institute of Standards and Technology introduced gasoline gallon equivalent as a metric for fuel economy for natural gas vehicles. NIST defined a gasoline gallon equivalent as 5.660 pounds of natural gas, and gasoline liter equivalent as 0.678 kilograms of natural gas.

2000: Petroleum-equivalent fuel economy

During the late 1990s and early 2000s several electric cars were produced in limited quantities as a result of the California Air Resources Board mandate for more fuel-efficient zero-emissions vehicles. Popular models available in California included the General Motors EV1 and the Toyota RAV4 EV. The U.S. DoE and EPA rating for on board energy efficiency for these electric vehicles was expressed as kilowatt hour/mile, the most commonly known metric in science and engineering for measuring energy consumption, and used as the billing unit for energy delivered to consumers by electric utilities.
In order to address the Corporate Average Fuel Economy regulations mandated by the U.S. Congress in 1975, the U.S. Department of Energy established in July 2000 a methodology for calculating the petroleum-equivalent fuel economy of electric vehicles on a well-to-wheel basis. The methodology considers the upstream efficiency of the processes involved in the two fuel cycles. The energy content of gasoline is reduced from 33,705 Wh/gal to 83% of that, or about 27,975 Wh/gal well-to-tank, to account for the energy used in refinement and distribution. Similarly, the energy value for electricity produced from fossil fuel is reduced to 30.3% due to energy lost in generation and transmission, according to the national average. This is normalized to the previous gasoline value, resulting in a well-to-vehicle gasoline-equivalent energy content of electricity of only 12,307 Wh/gal.
The formula also includes a "fuel content factor" of to benefit electric vehicles, raising the value from 12,307 to 82,049 Wh/gal. This reward factor is intended provide an incentive for vehicle manufactures to produce and sell electric vehicles, as a higher equivalent fuel economy for EVs improves the carmaker overall fleet fuel economy levels in complying with the CAFE standards, and Congress anticipated that such an incentive would help accelerate the commercialization of electric vehicles. The incentive factor chosen by DoE for EVs is the same factor already applied in the regulatory treatment of other types of alternative fuel vehicles. When all factors are considered in DoE's formula, the energy efficiency or equivalent fuel economy of electric vehicles increases, being calculated in miles per the petroleum-equivalency factor of 82,049 Wh/gal rather than miles per the usual gasoline gallon equivalent of 33,705 Wh/gallon, for the purposes of CAFE credits to manufacturers.

2007: X Prize

The Automotive X Prize competition was intended to encourage development of automobiles that would be capable of operating 100 miles on a gallon of gasoline. Comparison of electric vehicles to vehicles that carried their own engine was debated, since the notion of a miles per gallon equivalent as a metric for electric vehicles made the competition trivial for electric vehicles and a corresponding miles per gallon as a metric for the others extremely difficult for the others. Miastrada Company made the case that this defeated the purpose of the competition, to no avail. In April 2007, as part of Draft Competition Guidelines released at the New York Auto Show, MPGe was announced as the main merit metric for the Progressive Insurance Automotive X Prize, a competition developed by the X Prize Foundation for super-efficient vehicles that can achieve at least 100 MPGe. In February 2009, Consumer Reports announced that, as part of a partnership with the X Prize Foundation, they planned to report MPGe as one of several measures that will help consumers understand and compare vehicle efficiency for alternative fuel vehicles.