Use the Glossary of Terms to explain terms and abbreviations used in this list of Frequently Asked Questions.
The Frequent Questions page includes answers to common questions about the Guide. The questions are divided into these categories:
- Finding a Vehicle
- Vehicle Emissions and the Air Pollution Score
- Diesel Vehicles
- Alternative Fuels
- Fuel Economy and the Greenhouse Gas Scores
Finding a Vehicle
- How do I find the greenest vehicle possible?
- How can I look up a used car?
- Why are some vehicles sold only in some parts of the country?
- Why must I select a state before looking up a vehicle?
- Why can't I find some of the biggest trucks, SUVs and vans in this Guide?
Vehicle Emissions and the Air Pollution Score
- What are EPA's emission standards and why are they important?
- How are vehicles tested for emissions?
- What do the Air Pollution Scores mean?
- Why do some apparently identical vehicles have different Air Pollution Scores?
- What is EPA doing to control pollution from vehicles?
- The Air Pollution Score helps me compare my vehicle to others, but what are the actual emission standards for my vehicle?
- Why do we need scores at all? Don't all vehicles meet the requirements?
- Why do some diesel vehicles receive low Air Pollution Scores even though they have good fuel economy?
- Why aren't there many diesel cars and trucks listed?
- Is biodiesel fuel better to use than regular diesel fuel?
- Why is the fuel economy for a flex-fuel vehicle lower when using E85 than when using gasoline?
- What are the benefits of ethanol (E85)?
Fuel economy and the Greenhouse Gas Scores
- Why is fuel economy important?
- How are vehicles tested for fuel economy?
- Why is my fuel economy different than the estimates and how can I improve it?
- Why don't some vehicles have fuel economy numbers?
- Are there standards for fuel economy like there are for emissions?
How do I find the greenest vehicle possible?
We have identified the lowest emitting and most fuel efficient vehicles with a "SmartWay" designation. In addition, the best of those are identified as "SmartWay Elite." Look up all SmartWay and SmartWay Elite vehicles from the Home:Basic Search Look up the Greenest Vehicles page. Click on the logos to see more about the SmartWay rating system.
How can I look up a used car?
You can use this Guide to determine the Air Pollution and Greenhouse Gas Scores of any model year 2000 and later car or truck. There are no Air Pollution or Greenhouse Gas Scores for earlier models. However, there are other ways to look at the air pollution (emissions) and greenhouse gas (related to fuel economy) data for older models:
- Emissions: EPA annually posts detailed emission certification test information (actual vehicle test data) in a spreadsheet format at www.epa.gov/otaq/crttst.htm. This data is more technical in nature and may not be useful to the average consumer. Beginning in model year 2004, light-duty vehicles and trucks were required to meet “Tier 2” emission standards. Most vehicles built before 2000 were subject to the less stringent National Low Emission Vehicle (NLEV) or Tier 1 emission standards, and would score between 1 and 3 today. (See the detailed table of emission standards (6 pp, 54k, About PDF) for more information. )
- Fuel Economy: For fuel economy information on cars older than model year 2000, go to the EPA/DOE fuel economy web site at http://www.fueleconomy.gov. This site has fuel economy information for all vehicles going back to 1985.
California has emission standards that are similar to but not exactly the same as federal standards. In addition, other states are permitted to adopt the California standards. For the 2008 model year, the following states have adopted the California LEV 2 emission standards: NY, ME, MA, PA, RI, CT, VT. Also, states which border those states may also sell California-certified vehicles. Most manufacturers choose to design a single vehicle type that complies with both California and federal emission standards, thus the vehicles will be available nationwide. However, in some cases, manufacturers will design and certify a vehicle type for sale in California only or the "California states." Information about California's emission standards program can be found at www.arb.ca.gov/msprog/msprog.htm.
Why must I select a state before looking up a vehicle?
Emission requirements for vehicles sold in California and certain states that have adopted California's vehicle emission standards are different from those sold in the rest of the U.S. The law also allows states that border the so-called "California states” to sell California-certified vehicles. As a car shopper, all this makes it very complex to determine where you can purchase the cleanest vehicle that meets your needs. On the previous version of the Guide, after you selected a vehicle, we showed you maps where the vehicle could legally be sold, leaving it up to you to determine if the vehicle was available. In our redesign of the Guide, we now ask that you simply select the state or states where you may be purchasing your vehicle, and the program determines which vehicles you may be able to find in those states, taking some of the guesswork out of your decision. However, please be aware that just because a manufacturer is allowed to offer a vehicle for sale in a certain state does not mean that it must or will offer it for sale there. Sometimes, a manufacturer will certify a vehicle for sale in the entire 50-state region, but only plans to offer it in a limited area. We have no way of knowing these plans, so it's always best to check with your dealer about availability. Information about California's emission standards program can be found at www.arb.ca.gov/msprog/msprog.htm.
Some of the largest vans, pickup trucks, and sport utility vehicles are officially classified as "heavy-duty trucks." Heavy-duty trucks have different emission standards which cannot be easily compared to the standards of the light-duty trucks, and are thus not included in this Guide. They are also exempted from any federal fuel economy requirements. More information about the emission requirements for these and other heavy-duty vehicles can be found at www.epa.gov/otaq/hd-hwy.htm.
Vehicle Emissions and the Air Pollution ScoresWhat are EPA's emission standards and why are they important?
Cars, trucks and other mobile sources account for almost a third of the total air pollution in the United States. EPA's vehicle emission standards for cars and trucks have been in place since the early 1970's. Since that time, vehicle emissions standards have been made increasingly stringent to address this national air quality problem. View the summary of current and historical emission standards. (6 pp, 54k, About PDF)
EPA's newest standards, called "Tier 2," provide auto manufacturers with an array of emissions standards they can choose for any particular vehicle model, as long as all the new vehicles they sell in a given model year fall below a required average (bin 5). The emission standards are in effect from the time the vehicle is produced until the vehicle reaches the legally-defined end of its useful life (10 years or 120,000 miles for most cars) - manufacturers are responsible for designing vehicles that will pollute no more than the emission standard limits. More information about EPA's Tier 2 standards can be found here.
Due to its unique air quality problems, California has separate emission standards for cars and trucks. Manufacturers wishing to sell vehicles in California must certify that they comply with the California standards. Other states are permitted to adopt California emission standards as well. For the 2008 model year, the following states have adopted the California LEV 2 emission standards: NY, ME, MA, PA, RI, CT, VT. Also, states which border those states may also sell California-certified vehicles. Information about California's emission standards program can be found at www.arb.ca.gov/msprog/msprog.htm.
How are vehicles tested for emissions?
Before a vehicle manufacturer can offer a new vehicle for sale, EPA requires that various laboratory emission tests be conducted on a vehicle representative of the vehicles that will be sold to car buyers to ensure that the vehicles will meet the emission standards. The tests are designed to simulate a wide variety of actual on-road operating conditions (such as highway driving and city driving). The data from these tests are also used to calculate city and highway fuel economy (mpg) values which appear on the window stickers of new vehicles. More information about vehicle testing can be found here.
What do the Air Pollution Scores mean?
Each score reflects one set of emissions standards for four different air pollutants: oxides of nitrogen (NOx), carbon monoxide (CO), volatile organic compounds (VOC), and particulate matter (PM). The manufacturer is liable for ensuring that a properly maintained vehicle will emit no more than the given limit of each of these pollutants for each mile that the vehicle is driven. The Air Pollution Score which is a surrogate for the actual emission standards, is on a scale of 0-10, with 10 being the cleanest or best score.
Why do some apparently identical vehicles have different Air Pollution Scores?
A number of vehicles have different Air Pollution Scores even though they are, by all outward appearances, identical. This is usually due to the fact that there are separate EPA and California emission standards. Manufacturers wishing to sell vehicles in California as well as the rest of the U.S. must separately certify them to comply with EPA and California standards. California standards are generally more stringent than EPA standards due to the unique air quality problems in that state, so this can result in a higher Air Pollution Score for the California version. This does not necessarily mean that the vehicle sold in the rest of the U.S. is "dirtier." In general, if the Underhood Label ID is the same, the vehicle design will be the same as well, meaning that the vehicle has been designed to comply with both sets of standards, so that in reality, the emissions will be at the level of the more stringent of the two standards (California or EPA).
What is EPA doing to control pollution from vehicles?
EPA has a number of programs underway to ensure that vehicles operate cleanly from the time they are produced until the legally defined end of their useful life (10 years or 120,000 miles for most cars). Information about these and many other programs can be found in the Office of Transportation and Air Quality web site at www.epa.gov/otaq. A few of these are:
- New vehicle certification program: This program ensures that vehicles are designed to meet the emission standards set by Congress and EPA. For more information see http://www.epa.gov/otaq/cert.htm.
- On-board diagnostics (OBD): OBD is a computer-controlled system which alerts a driver via a dashboard light that there is a potential problem with the emissions control system of his or her vehicle. OBD is required on all 1994 and newer passenger cars and trucks. OBD systems were also required on trucks up to 14,000 pounds beginning in 2005. More information about these OBD requirements can be found at http://www.epa.gov/obd/regtech/light.htm. EPA has also proposed OBD requirements for heavy-duty trucks over 14,000 pounds beginning in the 2010 model year. More information on heavy-duty OBD can be found at http://www.epa.gov/obd/regtech/heavy.htm
- Inspection and maintenance: Many cities and metropolitan areas have established inspection and maintenance (I/M) programs that require owners to have their vehicle emissions checked periodically. For more information about I/M programs see www.epa.gov/otaq/im.htm.
- Emission recall: EPA monitors the emission performance of vehicles on the road to assure that they continue to comply with the emission standards. Vehicle manufacturers are required to build their vehicles to meet emission standards for the useful life of the vehicle. Under the Clean Air Act, if EPA determines that a substantial number of vehicles in a category or class do not meet the stadards in use even though they are properly maintained EPA can require the manufacturer to recall and fix the affected vehicles. View EPA's emission recall activities at www.epa.gov/otaq/recall.htm
- Emission warranty federally required emission control warranties protect you, the vehicle owner, from the cost of repairs for certain emission related failures that result from manufacturer defects in materials and workmanship or that cause your vehicle to exceed federal emission standards. There are two types of emission warranties: a defect warranty and a performance warranty. The defect warranty covers the repair of emission-related parts that become defective during normal vehicle operation. The performance warranty covers repairs that are necessary because the vehicle failed an EPA-approved I/M inspection. Check your owner's manual for more details about your emission warranties or see http://www.epa.gov/obd/warranties.htm.
The Air Pollution Scores help me compare my vehicle to others, but what are the actual emission standards for my vehicle?
The emission standards are numerical limits of the various regulated pollutants. A detailed table of emission standards effective for current and past model year cars and light trucks can be found in this Guide. (6 pp, 54k, About PDF)
Why do we need scores at all? Don't all vehicles meet the requirements?
All vehicles sold in the US must comply with federal emission standards. However, the standards are packaged in various “bins” that manufacturers can choose from, meaning that in a given model year, some vehicles will be cleaner than others. (See the detailed table of emission standards for more information.) (6 pp, 54k, About PDF) By means of the Air Pollution Score the Green Vehicle Guide shows you which vehicles are the cleanest.
Diesel VehiclesWhy do some diesel vehicles receive low Air Pollution Scores even though they have good fuel economy?
Despite their higher fuel efficiency which results in a better Greenhouse Gas Score, diesel vehicles emit higher levels of NOx (a lung irritant which contributes to smog formation) and particulate matter (a likely human carcinogen). Because these pollutants are more difficult to control in diesel exhaust, manufacturers certify them to comply with less stringent emission standards, resulting in lower Air Pollution Scores. However, manufacturers are working on developing more effective ways to control this pollution in diesels, and we expect to see higher scores in the future.
Why aren't there many diesel cars and trucks listed?
Because of the technical challenges associated with controlling NOx and PM emissions, manufacturers have not been able to design diesel vehicles that comply with the strictest EPA and California emission standards. However, we expect to see more diesels offered in the future as improvements to diesel emission control technology are made.
Is biodiesel fuel better to use than regular diesel fuel?
Biodiesel has the potential to provide a number of important benefits. As an alternative to diesel, it can help reduce U.S. dependence on foreign oil. Biodiesel also provides significant greenhouse gas (GHG) emission reductions. In addition, biodiesel offers several criteria emissions benefits for the existing vehicle fleet. It reduces emissions of carbon monoxide, particulate matter (PM), and sulfates, as well as hydrocarbon and air toxics emissions. On the other hand, a 2002 EPA summary analysis of existing data suggests that vehicles using biodiesel may emit slightly more oxides of nitrogen (NOx) (about two percent for B20 and 10 percent for B100). Subsequent studies have yielded mixed results, with some showing small increases and others showing small decreases. EPA plans a further investigation to fully assess this issue, including the emissions impact of using biodiesel in vehicles equipped with PM traps and NOx aftertreatment designed to meet strict new emission standards. Most diesel engines can run on biodiesel without needing any special equipment. If you are interested in using biodiesel in your vehicle or equipment, check with the manufacturer for any recommendations and information regarding engine warranties. In addition, once you have determined the proper blend for your vehicle, make sure to purchase your fuel from a reputable dealer selling commercial grade biodiesel. For more information see EPA's biodiesel fact sheet at http://www.epa.gov/smartway/growandgo/documents/factsheet-biodiesel.htm
Alternative FuelsWhy is the fuel economy for a flex-fuel vehicle lower when using E85 than when using gasoline?
Ethanol has a lower energy content than gasoline as measured in British Thermal Units per gallon, so you travel fewer miles per gallon when using a fuel that contains ethanol. Compared to gasoline, E85 typically gets about 25-30 percent fewer miles per gallon in ethanol flexible fuel vehicles.
What are the benefits of ethanol (E85)?
Ethanol contains less carbon than gasoline, and thus produces fewer greenhouse gas emissions (carbon-containing compounds such as CO2), than gasoline. It also can be produced from renewable sources such as corn or other vegetative matter, and thus helps to reduce dependency on fossil fuels.
Fuel Economy and the Greenhouse Gas ScoresWhy is fuel economy important?
Vehicles with lower fuel economy create more carbon dioxide - the most prevalent greenhouse gas - than vehicles with higher fuel economy. Every gallon of gasoline your vehicle burns puts about 20 pounds of carbon dioxide into the atmosphere because air has weight and mass, and it takes a lot of it to burn a gallon of gasoline. One of the most important things you can do to reduce your contribution to global warming is to buy a vehicle with higher fuel economy. The difference between 25 miles per gallon and 20 miles per gallon can amount to the prevention of 10 tons of carbon dioxide over a vehicle's lifetime. Buying a more fuel efficient vehicle will also will help to reduce our nation's dependence on fossil fuels. And of course, you will save money by having to fuel up less often.
How are vehicles tested for fuel economy?
The fuel economy estimates are determined by laboratory test procedures prescribed by EPA regulations. The test procedures are performed by auto manufacturers, and EPA audits the results at its own test laboratory to ensure manufacture accuracy. The vehicles are driven by professional drivers in controlled laboratory conditions. Using standardized test methods ensures that the fuel economy of all vehicles can be compared.
EPA recently revised the methods it uses to determine the city and highway estimates posted on the Green Vehicle Guide and on the window stickers of all new cars and light trucks. The methods are expected to provide consumers with better fuel economy estimates, based on more realistic driving conditions, such as cold temperatures, higher speeds, and use of air conditioning. The new methods take effect with 2008 and later models. More information about the new EPA testing methods can be found at http://www.epa.gov/fueleconomy/.
Why is my fuel economy different than the estimates and how can I improve it?
Even with the improved test methods for measuring fuel economy, no test can simulate all the possible conditions that affect fuel economy such as climate, driver behavior, road condition, and car care habits. Thus your actual mileage will always vary some from the estimates. Tips for improving fuel economy can be found on the EPA-DOE fuel economy web site at http://www.fueleconomy.gov.
Why don't some vehicles have fuel economy numbers?
Federal fuel economy requirements currently apply only to light-duty vehicles and light-duty trucks weighing under 8,500 pounds (gross vehicle weight rating). This excludes some of the heaviest pickups, vans and SUVs. However, beginning with 2011 models, fuel economy estimates will be required for vehicles known as "Medium Duty Passenger Vehicles," which are SUVs and vans rated at 10,000 pounds (gross vehicle weight rating).
Are there standards for fuel economy like there are for emissions?
Yes. Through the Corporate Average Fuel Economy (CAFE) program, the federal government has established separate fuel economy standards for cars and trucks. The standards are for the average fuel economy of the entire fleet of cars or trucks for a given model year. A penalty is assessed if a manufacturer's fleet does not meet the average standard. The standards are enforced by the U.S. Department of Transportation (DOT). The fuel economy values on which the CAFE standards are based are not comparable to the city and highway estimates given in the Green Vehicle Guide, because they are determined using different calculation methods. For more information on CAFE go to DOT's CAFE web site.