Glossary of Terms
Air Pollution Score
The Air Pollution Score is based on the government emission standards for which the vehicle was certified to comply with and reflects vehicle tailpipe emissions that contribute to local and regional air pollution, creating problems such as haze, and health issues. (Note: see About the Ratings for more information).
Certification Sales Region
The area of the country where the vehicle can legally be sold. New federally certified vehicles can be sold in all states except California and those states that have adopted California emission standards. New California vehicles can be sold in California and in states that have adopted the California emission standards as well as bordering states. Manufacturers are not required to offer vehicles for sale in those areas, however, so check with local dealers for availability.
City Fuel Economy
Estimated miles-per-gallon in the city. City Fuel Economy represents urban driving, in which a vehicle is started after not running for 12 hours and driven in stop and go traffic.
Combined Fuel Economy
Combined Fuel Economy means the fuel economy from driving a combination of 55% city and 45% highway miles and is calculated as follows:
1 / [(0.55/city mpg) + (0.45/highway mpg)]
Some transmissions can disengage from the drive-shaft in the event the drive-shaft speed is greater than the transmission output speed. This freewheeling, if applicable, may have safety lock out features.
The manner in which mechanical power is directly transmitted from the drive shaft to the wheels. The following codes are used in the drive field:
- AWD = All Wheel Drive: four-wheel drive automatically controlled by the vehicle powertrain system
- 4WD = 4-Wheel Drive: driver selectable four-wheel drive with 2-wheel drive option
- 2WD = 2-Wheel Drive
Emission Certification Standard
EPA and California-required standards. The names refer to tables of numerical limits for the various air pollutants allowed by the standards. (Note: see About the Ratings for more information).
Descriptions provided to EPA by manufacturers to differentiate models with different mpg values but otherwise identical. One common entry is the driving range on a tank of E85 fuel (ex. "RNG=340")
A vehicle’s engine size is measured by displacement, normally given in units of liters (3.2L = 3.2 liters) or number of cylinders. Larger, more powerful engines usually have more cylinders than smaller engines.
EPA Fuel Economy Estimates/MPG Estimates
EPA estimates are based upon vehicle-specific data from tests designed to replicate real-world conditions, which can significantly affect fuel economy: high-speed/rapid acceleration driving, use of air conditioning, and cold temperature operation. Other conditions such as road grade, wind, tire pressure, and fuel property differences are also considered.
Estimated Annual Fuel Costs
An estimate of the annual cost to fuel the vehicle, based on the vehicle’s combined city/highway fuel economy. The fuel cost assumes the vehicle is driven 15,000 miles in a year. The price per gallon of fuel is determined by the Department of Energy.
The amount of fuel consumed in a given distance (e.g., gallons per 100 miles). This is the inverse of fuel economy.
Fuel Economy refers to the average number of miles traveled per gallon of fuel consumed.
Fuel types include gasoline, diesel, ethanol, compressed natural gas(CNG), electric, and hybrid.
Greenhouse Gas Score
This score reflects fuel emissions of carbon dioxide (CO2) and other greenhouse gases. (Note: see About the Ratings for more information).
Greenhouse Gases Emitted
Vehicles create greenhouse gases as a result of fuel combustion. Greenhouse gases trap heat in the atmosphere, thereby creating a greenhouse effect. Some greenhouse gases occur naturally and are emitted in the atmosphere through natural processes and human activities. Other greenhouse gases are created only through human activities. Scientists are certain that human activities are changing the composition of the atmosphere and that increasing the concentration of greenhouse gases will eventually change the planet’s climate. Greenhouse gases emitted from vehicles include carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) and relatively small amounts of hydroflurocarbons (HFCs) and black carbon. The Green Vehicle Guide currently accounts for CO2, CH4 and N2O. The value shown gives tons of greenhouse gases emitted by the vehicle if it were driven 15,000 miles per year. Tons are expressed as CO2-equivalent emissions factoring in the global warming potential for each gas.
Highway Fuel Economy
Estimated miles-per-gallon on the highway. Highway fuel economy represents a mixture of rural and interstate highway driving in a warmed-up vehicle, typical of longer trips in free flowing traffic at higher than city speeds.
Hybrid electric vehicles combine features of internal combustion engines and electric motors. Unlike 100% electric vehicles, hybrid vehicles do not need to be plugged into an external source of electricity to be recharged. Most hybrid vehicles operate on gasoline.
For cars, this is trunk luggage volume. For hatchbacks and station wagons, this is the luggage volume behind the 2nd row of seats. (Ref SAE J1100) .
MPG (Miles Per Gallon)
Miles per gallon, a measure of fuel economy.
"Make" is the manufacturing company, or, in some cases, a division of a manufacturing company, such as "Chevrolet", "Acura", or "Jeep".
"Model" is the name of the vehicle. In some cases, manufacturers subdivide a model according to various trim levels which do not affect the emissions or fuel economy levels. Not all of these model name subdivisions may appear in the Guide, but the emissions and fuel economy will be the same.
Model year refers to the actual annual production period (year) as determined by the manufacturer.
Number of Transmission Modes
Multimode transmissions have an operator selectable feature that changes the transmission parameters such as gear ratios or shift speed points (e.g., fuel economy or performance mode that changes shift schedule). Electronic overdrive and variable lockup calibrations do not constitute multimode transmissions.
This is the sum of the front and rear seat passenger volumes, if applicable. If the carline contains more than one body style, the passenger volume is the arithmetic average. ( Ref. SAE J1100)
SmartWay is a designation earned by those vehicles that have combined Air Pollution and Greenhouse Gas Scores that place them in the top tier (approximately the top 20%) of environmental performers. SmartWay Elite is reserved for the best of the best (for more information see: “About the Ratings”).
Smog Forming Pollutant
Smog forming pollution is created by two types of vehicle emissions – hydrocarbons (including non-methane organic compounds, or NMOG) and oxides of nitrogen (NOx) – which, when combined with sunlight, form smog. Smog can irritate lungs, eyes, and other tissues. The Air Pollution Score reflects this type of pollution. The value represents pounds of NOx and NMOG emitted by the vehicle if it were driven 15,000 miles per year.
The maximum allowable emissions in grams per mile for each air pollutant. The Air Pollutants are:
- NOx = Oxides of Nitrogen: NOx is a lung irritant. When combined with hydrocarbons and sunlight, NOx compounds form smog.
- CO = Carbon Monoxide: A colorless, odorless, poisonous gas.
- NMOG = Non-Methane Organic Compounds: Compounds containing carbon which, when combined with NOx in the presence of sunlight, form smog.
- PM = Particulate Matter: Tiny particles of solid matter that lodge in the lungs and form deposits on buildings. PM is likely a cancer-causing carcinogen.
The gearbox that provides different gear ratios between the engine and the drive wheels including reverse gear.
|Auto-AV||Automatic variable gear ratio|
Overdrive, in general, refers to a top gear ratio of less than one. This refers to a transmission gear ratio and not necessarily a separate mechanical unit, as in the past. If a gear ratio is less than 1, the transmission output speed is greater than the input speed. Lower gear ratios will increase high speed fuel economy at the expense of torque.
A means of increasing engine power output via precompression of intake air. Superchargers typically use a mechanical means to increase air density, whereas a turbocharger uses waste exhaust energy. Engines may incorporate multiple and or both super and turbochargers.
Underhood Label ID
Located on a label in the engine compartment, the label indicates engine family or EPA vehicle test group. The following image shows a sample Underhood Label ID:
Valves Per Cylinder
The total number of intake and exhaust valves per engine cylinder.
Variable Lock-Up Point
Typically, transmissions with electronic transmission control, have more than one set of torque converter lockup preconditions. A variable torque converter lockup strategy can be either computer controlled, continuously variable, or discrete.
A class of vehicle determined by commonly used sales groupings, including Large Cars, Midsize Cars, Minivans, Pickup Trucks, Small Cars, Special Purpose Vehicles, Sports Utility Vehicles, Station Wagons, and Vans.