page_title: Fuel economy in automobiles
section_title: Electric vehicles and hybrids
hierarchical_section_title: Fuel economy in automobiles / Fuel economy standards and testing procedures / United States / Electric vehicles and hybrids
caption_attribution_description: English: EPA fuel economy and environmental comparison label for the 2011 Chevrolet Volt (Dual fuel vehicle electricity-gasoline)
context_page_description: The fuel economy of an automobile relates distance traveled by a vehicle and the amount of fuel consumed. Consumption can be expressed in terms of volume of fuel to travel a distance, or the distance travelled per unit volume of fuel consumed. Since fuel consumption of vehicles is a significant factor in air pollution, and since importation of motor fuel can be a large part of a nation's foreign trade, many countries impose requirements for fuel economy. Different methods are used to approximate the actual performance of the vehicle. The energy in fuel is required to overcome various losses encountered while propelling the vehicle, and in providing power to vehicle systems such as ignition or air conditioning. Various strategies can be employed to reduce losses at each of the conversions between the chemical energy in the fuel and the kinetic energy of the vehicle. Driver behavior can affect fuel economy; maneuvers such as sudden acceleration and heavy braking waste energy.
  Electric cars do not directly burn fuel, and so do not have fuel economy per se, but equivalence measures, such as miles per gallon gasoline equivalent have been created to attempt to compare them.
context_section_description: Following the efficiency claims made for vehicles such as Chevrolet Volt and Nissan Leaf, the National Renewable Energy Laboratory recommended to use EPA's new vehicle fuel efficiency formula that gives different values depending on fuel used. In November 2010 the EPA introduced the first fuel economy ratings in the Monroney stickers for plug-in electric vehicles.
  For the fuel economy label of the Chevy Volt plug-in hybrid EPA rated the car separately for all-electric mode expressed in miles per gallon gasoline equivalent (MPG-e) and for gasoline-only mode expressed in conventional miles per gallon. EPA also estimated an overall combined city/highway gas-electricity fuel economy rating expressed in miles per gallon gasoline equivalent (MPG-e). The label also includes a table showing fuel economy and electricity consumed for five different scenarios: 30 miles (48 km), 45 miles (72 km), 60 miles (97 km) and 75 miles (121 km) driven between a full charge, and a never charge scenario. This information was included in order to make the consumers aware of the variability of the fuel economy outcome depending on miles driven between charges. Also the fuel economy for a gasoline-only scenario (never charge) was included. For electric-only mode the energy consumption estimated in kWh per 100 miles (160 km) is also shown.
  For the fuel economy label of the Nissan Leaf electric car EPA rated the combined fuel economy in terms of miles per gallon gasoline equivalent, with a separate rating for city and highway driving. This fuel economy equivalence is based on the energy consumption estimated in kWh per 100 miles, and also shown in the Monroney label.
  In May 2011, the National Highway Traffic Safety Administration (NHTSA) and EPA issued a joint final rule establishing new requirements for a fuel economy and environment label that is mandatory for all new passenger cars and trucks starting with model year 2013, and voluntary for 2012 models. The ruling includes new labels for alternative fuel and alternative propulsion vehicles available in the US market, such as plug-in hybrids, electric vehicles, flexible-fuel vehicles, hydrogen fuel cell vehicle, and natural gas vehicles. The common fuel economy metric adopted to allow the comparison of alternative fuel and advanced technology vehicles with conventional internal combustion engine vehicles is miles per gallon of gasoline equivalent (MPGe). A gallon of gasoline equivalent means the number of kilowatt-hours of electricity, cubic feet of compressed natural gas (CNG), or kilograms of hydrogen that is equal to the energy in a gallon of gasoline.
  The new labels also include for the first time an estimate of how much fuel or electricity it takes to drive 100 miles (160 km), providing US consumers with fuel consumption per distance traveled, the metric commonly used in many other countries. EPA explained that the objective is to avoid the traditional miles per gallon metric that can be potentially misleading when consumers compare fuel economy improvements, and known as the "MPG illusion" – this illusion arises because the reciprocal (i.e. non-linear) relationship between cost (equivalently, volume of fuel consumed) per unit distance driven and MPG value means that differences in MPG values are not directly meaningful – only ratios are (in mathematical terms, the reciprocal function does not commute with addition and subtraction; in general, a difference in reciprocal values is not equal to the reciprocal of their difference). It has been claimed that many consumers are unaware of this, and therefore compare MPG values by subtracting them, which can give a misleading picture of relative differences in fuel economy between different pairs of vehicles – for instance, an increase from 10 to 20 MPG corresponds to a 100% improvement in fuel economy, whereas an increase from 50 to 60 MPG is only a 20% improvement, although in both cases the difference is 10 MPG. The EPA explained that the new gallons-per-100-miles metric provides a more accurate measure of fuel efficiency – notably, it is equival
caption: 2010 Monroney sticker for a plug-in hybrid showing fuel economy in all-electric mode and gas-only mode.
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