Mercedes Mullins
The fuel economy of vehicles is an important metric that helps consumers make informed decisions about their purchases. It is also a key indicator of a vehicle's environmental impact. While it would be impractical to test every car on the road, all light-duty vehicles are required by law to have their fuel-economy estimates certified by the U.S. Environmental Protection Agency (EPA). The EPA uses well-defined tests, conducted under controlled conditions in a laboratory, to establish fuel mileage. These tests are designed to replicate the driving experience, with city and highway cycles simulating typical trips. Vehicle manufacturers also conduct their own tests and report the results to the EPA, who then review and confirm a portion of these results through additional testing. The EPA's National Vehicle and Fuel Emissions Laboratory (NVFEL) plays a crucial role in ensuring that vehicles sold in the U.S. comply with federal emissions and fuel economy standards.
| Characteristics | Values |
|---|---|
| Who conducts the tests? | The Environmental Protection Agency (EPA) conducts tests on around 250 vehicles per year, with about 75% being random checks on the manufacturer's results. The EPA also conducts tests in response to consumer reports of fuel economy being inconsistent with stated ratings. |
| Vehicle manufacturers also conduct tests on their own vehicles and submit the results to the EPA. | |
| Who is responsible for the data? | The EPA provides fuel economy data to the Department of Energy (DOE), the Department of Transportation (DOT), and the Internal Revenue Service (IRS). |
| The DOE publishes the fuel economy label values in the annual Fuel Economy Guide. | |
| The DOT receives the manufacturer's fleet average fuel economy from the EPA and determines compliance with federal corporate average fuel economy (CAFE) standards. | |
| The IRS collects "Gas Guzzler" taxes. | |
| Which vehicles are tested? | All light-duty vehicles are required by law to have their fuel economy estimates certified by the EPA. |
| Vehicles that exceed certain weight limits, such as large SUVs, passenger vans, and pickup trucks, are not required to be tested and their fuel consumption ratings may not appear in official guides. | |
| Plug-in hybrids and electric vehicles (EVs) also receive estimates for electric operation, expressed in MPGe. | |
| Testing procedures | Tests are conducted under controlled conditions in a laboratory using a series of tests specified by federal law. |
| Vehicles are placed on a dynamometer, which simulates the driving environment. | |
| Engineers adjust for factors such as wind resistance, vehicle weight, and aerodynamics. | |
| A driver operates the vehicle through standardized driving routines or "cycles" that simulate typical trips, including specific speeds, acceleration, temperatures, and use of air conditioning. | |
| The EPA's tests include a "city cycle" with an average speed of 21 mph and a "highway cycle" with an average speed of 48 mph. | |
| A hose is connected to the tailpipe to collect engine exhaust and measure carbon and other air pollutants. | |
| Limitations and considerations | The EPA's tests may not fully represent real-world driving conditions, such as low and high speeds experienced in dense traffic or on highways. |
| The EPA's ratings are mostly self-reported by auto manufacturers, and the EPA only confirms approximately 15%-20% of all test results. |
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What You'll Learn
Fuel economy testing methods
During the testing process, the vehicle's drive wheels are placed on a machine called a dynamometer, which simulates the driving environment. Engineers adjust the amount of energy required to move the rollers to account for wind resistance and the vehicle's weight. A driver then runs the vehicle through standardized driving routines called cycles or schedules, which simulate typical trips in the city or on the highway. Each cycle specifies the speed the vehicle must travel at each second of the test.
The carbon in the exhaust is measured to calculate the amount of fuel burned during the test. This is done by connecting a hose to the tailpipe to collect engine exhaust. Other air pollutants are measured using gas analyzers, and fine particles (particulate matter, PM) are weighed in a special "clean room." For vehicles that run on non-carbon fuels, such as electric vehicles, a different method is used.
In addition to the standard laboratory tests, some organizations conduct their own real-world highway fuel-economy tests to provide a more accurate representation of how people drive outside of controlled conditions. These tests are designed to address the shortcomings of the EPA tests, which do not include speeds as low as those experienced in areas of dense traffic or as high as those typically driven on highways.
It is worth noting that the testing procedures for heavy-duty trucks and buses differ from those for light-duty vehicles. Organizations such as SwRI conduct year-round testing on public roadways and closed test tracks, simulating long-haul routes or other appropriate driving cycles to evaluate fuel consumption.
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Who conducts the tests?
Fuel economy tests are conducted by the Environmental Protection Agency (EPA) at its National Vehicle and Fuel Emissions Laboratory in Ann Arbor, Michigan. The EPA reviews the results and confirms 15-20% of them through its own tests. The vehicles are tested in a dynamometer test cell, which works like a treadmill for cars.
The EPA's tests are conducted under controlled conditions in a laboratory using a series of tests specified by federal law. The tests are designed to mimic the basic commute drivers experience daily, with "city" and "highway" driving cycles. These cycles simulate typical trips, including specific speeds and acceleration, different temperatures, and the use of air conditioning. The EPA also conducts a high-speed" test that includes more rapid acceleration and a top speed of 80 mph.
While the EPA conducts its own tests, the majority of the ratings are self-reported by auto manufacturers. Manufacturers test their own vehicles, typically pre-production prototypes, and report the results to the EPA. The EPA then reviews and confirms a portion of these results through its own tests.
In addition to the EPA, organizations like Car and Driver and AAA also conduct their own fuel economy tests. Car and Driver, for example, has created its own uniform highway fuel-economy test, which involves running all tests at a GPS-verified 75 mph on the same 200-mile out-and-back loop on Michigan's I-94 highway. AAA, on the other hand, evaluates vehicles by comparing their EPA fuel economy ratings with actual owner-reported gas mileage as listed on the EPA's website.
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Vehicles exempt from testing
In the United States, all light-duty vehicles are required by law to have their fuel-economy estimates certified by the Environmental Protection Agency (EPA). The EPA's National Vehicle and Fuel Emissions Laboratory (NVFEL) tests new cars and trucks sold in the U.S. to ensure they comply with federal emissions and fuel economy standards. Manufacturers test their own vehicles and report the results to the EPA, which reviews the results and confirms about 15-20% of them through its own tests.
However, certain vehicles are exempt from these testing requirements. Low-volume manufacturers, or those that manufacture or will manufacture fewer than 10,000 vehicles in the applicable model years, can petition for exemption from the Corporate Average Fuel Economy (CAFE) standards. NHTSA has considered manufacturers' use of fuel-economy-improving technologies for weight reduction, aerodynamic improvements, engine improvements, and transmission improvements. Off-cycle and air conditioning (A/C) efficiency improvement technologies also fall within the scope of technologies that manufacturers must discuss in their petitions.
In New York State, most light-duty vehicles (passenger cars, vans, and pick-up trucks) are required to have an emissions inspection through NYVIP. However, certain vehicles are exempt from these emissions testing requirements, including:
- Electric-powered vehicles
- Motorcycles
- Vehicles with historic and farm registrations
- Diesel-powered vehicles greater than 8,500 lbs. GVWR registered Upstate
- Vehicles 25 model years and older (for example, during the calendar year 2024, model year 1999 and older vehicles)
It is important to note that while some vehicles may be exempt from specific emissions or fuel economy testing requirements, they may still be subject to annual safety inspection requirements.
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How to compare vehicles
When it comes to comparing vehicles, particularly in terms of fuel economy, there are several factors and methods to consider. Official testing is carried out by the Environmental Protection Agency (EPA) in the US, which publishes an annual Fuel Economy Guide. The EPA's National Vehicle and Fuel Emissions Laboratory (NVFEL) tests new cars and trucks to ensure they meet federal emissions and fuel economy standards. Manufacturers test their own vehicles and provide the data used for labelling, which the EPA confirms through its own tests on a small percentage of vehicles. The EPA's tests are carried out in controlled conditions in a laboratory, using a dynamometer (a machine that simulates the driving environment).
However, these tests may not always reflect real-world driving conditions and experiences. For instance, the EPA's test cycles do not include speeds as low as those found in dense traffic or as high as those typically driven on US highways. As such, some organisations, like Car and Driver, have created their own uniform tests to compare vehicles. Car and Driver runs tests on a 200-mile loop of Michigan's I-94 highway, at a GPS-verified speed of 75 mph, to provide a more realistic comparison of fuel economy.
When comparing vehicles, there are several key factors to consider:
- Fuel economy: This is an important factor, especially when considering the cost of running a vehicle. Official sources, like the US Department of Energy, provide tools to compare the fuel economy of different vehicles.
- Fuel type: Different fuel types, such as gasoline, diesel, hybrid, or electric, will impact the fuel economy and running costs. Electric vehicles, for example, may enter a low-speed limp mode when the battery is low, which can affect their performance on highways.
- Driving conditions: Consider the typical driving conditions you will encounter. Official tests may not always reflect your everyday driving, so it is worth looking at reviews and tests that mirror your usual driving environment, such as city driving or highway cruising.
- Storage and space: The size and storage capacity of a vehicle are practical considerations. Think about how much space you need for passengers and cargo, and compare vehicle dimensions and layouts to find the best fit.
Comparing vehicles involves weighing up various factors, and it is important to consider official tests, real-world reviews, and your own personal needs to make an informed decision.
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Real-world testing
Fuel economy is an important factor when choosing a car, as it determines how many miles you can get from a gallon of fuel. Official fuel economy figures are often based on laboratory tests, which may not accurately reflect real-world driving conditions. To address this, organisations like What Car? and Car and Driver have developed their own real-world testing procedures to provide consumers with more accurate fuel economy data.
What Car? has introduced a tool called Real MPG, which is based on real-world driving data from different types of roads. They test each car by leaving it to 'soak' at 23 degrees, usually overnight, to ensure that every car starts the test with the same engine temperature. They then measure tailpipe emissions, including carbon dioxide, nitrogen oxides, carbon monoxide, and hydrocarbons, on a second-by-second basis. This data is used to calculate fuel consumption for different phases of driving (town, motorway, and rural) and provide a more realistic fuel economy figure.
Car and Driver also conducts real-world highway fuel economy tests to supplement the EPA estimates. They measure every nook and cranny of the vehicle to provide accurate comparisons of cargo and storage space. They also weigh the vehicle to calculate loads for replicating resistive forces, simulating the extra work the engine would need to do to haul a heavier car. They then conduct a fuel loop test, recording the vehicle's performance and calculating its range based on the fuel tank size.
In addition to these independent tests, the EPA has also made efforts to incorporate more real-world scenarios into its testing protocols. They conduct random checks on manufacturer results and investigate consumer reports of fuel economy inconsistencies. Three additional tests have been introduced: a "high-speed" test with rapid acceleration and a top speed of 80 mph, an "air conditioning" test performed at 95°F, and a "cold" test at 20°F. These tests provide data for the fuel economy labels on new vehicles, helping consumers make informed choices.
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Frequently asked questions
No, vehicle manufacturers are not required to submit fuel consumption data for certain types of vehicles, such as sport utility vehicles (SUVs) and passenger vans with a gross vehicle weight rating (GVWR) of 4,536 kg (10,000 lbs) or more.
The Environmental Protection Agency (EPA) governs the fuel-economy ratings listed on vehicle window stickers. The EPA conducts its own tests on a small percentage of vehicles, while the majority of the data is self-reported by the manufacturers.
Fuel economy tests provide consumers with information about a vehicle's fuel efficiency. The tests are designed to simulate real-world driving conditions and help motorists make informed decisions about vehicle ownership costs.
