Rajan Wilcox
Fuel economy tests are conducted to determine a vehicle's fuel efficiency and provide consumers with an estimate of its performance in mixed driving conditions. The tests are carried out by organizations like the US Environmental Protection Agency (EPA) and independent reviewers, using a combination of laboratory and real-world driving tests. Laboratory tests are performed on a rolling road or dynamometer, simulating driving environments and standardized driving routines, while real-world tests involve tracking fill-ups and mileage on test vehicles. The results are used to estimate fuel economy, with variables like driving style and distance traveled considered. However, the gap between official figures and actual fuel consumption has been a concern, leading to the introduction of more stringent test procedures like the WLTP, which aims to provide more realistic and achievable fuel economy figures for new cars.
| Characteristics | Values |
|---|---|
| Who conducts the test | US Environmental Protection Agency (EPA), vehicle manufacturers, Car and Driver, Which?, and The AA |
| Testing location | EPA's National Vehicle and Fuel Emissions Laboratory in Ann Arbor, Michigan |
| Vehicles tested | Carbon-based fuel vehicles (e.g., gasoline, diesel, natural gas), non-carbon fuel vehicles, plug-in hybrids, and electric vehicles |
| Testing method | Laboratory testing using a dynamometer, on-road testing, WLTP, RDE, NEDC, and WLTC |
| Data collected | Fuel economy estimates, fuel consumption, emissions, sound-pressure level, mileage, and fill-ups |
| Results | Fuel economy data, fuel economy label values, fleet average fuel economy, and conformity factor |
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What You'll Learn
Fuel economy estimates
The EPA's testing methods have evolved to incorporate more real-world scenarios. The initial basis for EPA ratings was the "city" and "highway" driving cycles, with average speeds of 21 mph and 48 mph, respectively. To enhance accuracy, the EPA adopted new methods in 2008, adding a "high-speed" test that includes rapid acceleration and a top speed of 80 mph. However, it's important to note that the EPA conducts original tests on only about 250 vehicles annually, with the majority of its ratings being self-reported by automakers.
While the EPA's estimates are widely used, there are alternative sources for fuel economy information. Car and Driver, for instance, tracks all fill-ups and mileage on test vehicles, including electric vehicles and plug-in hybrids, to provide observed fuel-economy numbers. They also created their own uniform highway fuel-economy test, running tests at a GPS-verified 75 mph on a 200-mile loop on Michigan's I-94 highway. This approach addresses the limitations of EPA tests, which may not fully reflect real-world driving conditions, speeds, and traffic variables.
In addition to these sources, organisations like AAA contribute to fuel economy insights by evaluating vehicles and comparing EPA ratings with actual owner-reported gas mileage. This provides a broader perspective, as 81.8% of drivers reported better fuel economy than EPA estimates, while 16% reported lower fuel economy. AAA's analysis also identified variations based on vehicle type, with diesel engines outperforming EPA ratings and minivans falling short in real-world fuel efficiency.
With the introduction of the WLTP (Worldwide Harmonised Light Vehicle Test Procedure) test procedure, which replaces the NEDC (New European Driving Cycle), there is an expectation of more realistic and achievable official fuel consumption figures for new cars. This addresses the growing gap between official figures and actual fuel consumption, which has widened over the years. The WLTP test procedure takes into account various driving conditions, providing figures for low, medium, high, and extra-high-speed driving, giving consumers a more comprehensive understanding of a vehicle's fuel economy.
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Real-world testing
In response to this need for real-world data, the Australian Automobile Association (AAA) has launched a "real-world" testing program with a \$14 million grant from the federal government. Over four years (2023-2026), AAA plans to test around 200 different vehicles, including cars, utes, and electric vehicles, on Australian roads to verify their fuel consumption and emissions. This follows a pilot program conducted by AAA in 2017. The test vehicles will be fitted with a portable emissions measurement system, and the testing protocol will be based on international regulations with adjustments for Australian conditions. The results will be published on a separate website from the Green Vehicle Guide to minimise confusion with lab test data.
The AAA's real-world testing program addresses the issue of advertised fuel economy figures, which are typically obtained from laboratory tests and may not accurately represent a vehicle's performance on the road. In Australia, it was found that the average car consumed 23% more fuel than its advertised sticker result, and in some cases, vehicles performed even worse, with a diesel SUV consuming 59% more fuel than its official result. These discrepancies can impact consumers' ability to make informed choices when purchasing a vehicle.
In the United States, the Environmental Protection Agency (EPA) conducts original tests on about 250 vehicles annually, with a focus on random checks of manufacturer results. The EPA also addresses consumer reports of fuel economy inconsistent with stated ratings. To enhance the accuracy of fuel economy ratings, the EPA adopted new methods in 2008, including additional tests for high-speed driving, air conditioning use, and cold temperatures, which better reflect real-world driving scenarios. These tests are conducted in a laboratory setting using a dynamometer, a machine that simulates the driving environment, and specific driving "schedules" that mimic typical city and highway trips.
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Official consumption figures
The EPA's tests are conducted inside on a treadmill for vehicles, eliminating variables like temperature and traffic. While these scientific methods provide an excellent way to directly compare two vehicles, they may not reflect real-world driving conditions, with test cycles not including speeds as low as those experienced in dense traffic or as high as those on U.S. highways. This discrepancy has led to criticism of car manufacturers for misleading claims, with a widening gap between official figures and actual fuel consumption.
To address this, The AA introduced the WLTP (Worldwide Harmonised Light Vehicle Test Procedure), which replaces the NEDC (New European Driving Cycle) to provide more realistic and achievable official fuel consumption figures for new cars. The WLTP includes a two-step "conformity factor" to account for higher RDE emissions, which are emissions measured during real-world driving. From September 2017, RDE emissions could be up to 2.1 times (110%) higher, and from January 2020/2021, they could be up to 1.5 times (50%) higher for new models.
For consumers, it is essential to consider that official consumption figures may not always align with their real-world fuel economy. Websites like Real MPG (Honest John) and Spritmonitor.de offer insights by collecting user-submitted fuel consumption data, providing a broader perspective on the fuel economy of specific vehicles.
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Emissions testing
The US Environmental Protection Agency (EPA) is responsible for testing and analysing vehicles, engines, and fuels to ensure they meet federal and fuel economy standards. The EPA's National Vehicle and Fuel Emissions Laboratory (NVFEL) tests vehicles, engines, and fuels to ensure they meet federal and fuel economy standards. The NVFEL is a state-of-the-art facility that provides a wide range of analytical testing and engineering services to support the EPA's regulatory goals. The EPA also develops new technologies to reduce emissions and increase fuel efficiency.
The NVFEL evaluates emission control technology, tests vehicles, engines, and fuels, and determines compliance with federal emissions and fuel economy standards. The laboratory tests new cars and trucks sold in the US to ensure they comply with federal emissions and fuel economy standards. The EPA confirms the accuracy of fuel economy test results submitted by each manufacturer. They also conduct testing of used vehicles, typically between one and seven years old, to survey the effectiveness of the vehicle's emissions control systems over 120,000 to 150,000 miles of useful life.
The EPA defines the methods used to calculate the fuel economy estimates that are posted on the window stickers of new cars and light trucks. Automakers must follow specific test procedures and submit fuel economy data to the EPA annually for all their models. The EPA confirms approximately 15% of all test results, but manufacturers are responsible for providing the fuel economy data used for labelling.
The EPA's testing procedures include testing vehicles in a dynamometer test cell, which works like a treadmill for cars. A driver operates the vehicle following a "schedule" that simulates a typical trip, including specific speeds, acceleration, and temperatures, as well as the use of air conditioning. The EPA also collects engine exhaust through a hose connected to the tailpipe to calculate the amount of fuel burned and measure other air pollutants and fine particles.
While the EPA's testing methods provide a standardised way to compare vehicles, they may not always reflect real-world driving conditions. The EPA's tests do not include low or high speeds experienced in areas of dense traffic or on highways. As a result, organisations like Car and Driver have developed their own uniform highway fuel-economy tests to provide a more realistic assessment of fuel economy.
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Motorway driving cycle
The fuel economy and emissions of cars are tested through standard procedures before they are authorised for sale in many countries. These tests are conducted under laboratory conditions using a chassis dynamometer. However, the specific test methods and cycles (vehicle running patterns) vary among countries and regions.
One such test cycle is the Extra Urban Driving Cycle (EUDC), which is designed to account for aggressive, high-speed driving modes. The maximum speed of the EUDC cycle is 120 km/h, with an alternative cycle for low-powered vehicles limited to 90 km/h. This test cycle falls under the United Nations Economic Commission for Europe Regulations, which specify the procedures for determining fuel consumption and CO2 emissions from light vehicles.
In the United States, the Environmental Protection Agency (EPA) has developed its own set of test procedures, including the EPA Highway Fuel Economy Cycle, a chassis dynamometer driving schedule for determining the fuel economy of light-duty vehicles. This cycle represents a mixture of rural and interstate highway driving with a warmed-up engine, typical of longer trips in free-flowing traffic.
Additionally, the US has the Federal Test Procedure (FTP-75), which has been used for emission certification in light-duty vehicles. To address the shortcomings of the FTP-75 in representing aggressive, high-speed driving, two Supplemental Federal Test Procedures (SFTP) have been introduced: the US06 and the SC03. The US06 specifically targets high-speed and high-acceleration driving behaviour, speed fluctuations, and driving behaviour following these conditions.
While these tests provide valuable insights into fuel economy and emissions, it is important to recognise that test methods and cycles can vary, and real-world driving conditions may differ from the simulated environments.
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Frequently asked questions
A fuel economy test is a series of tests carried out under controlled conditions in a laboratory to measure a vehicle's fuel economy.
The Environmental Protection Agency (EPA) carries out tests on vehicles at its National Vehicle and Fuel Emissions Laboratory (NVFEL) in Ann Arbor, Michigan. Manufacturers also test their own vehicles and submit the results to the EPA.
The EPA uses a computer-controlled chassis dynamometer to replicate the driving experience. The tests are designed to mimic the basic commutes drivers experience daily, including "city" and "highway" driving cycles, with specific speeds and acceleration.
In a AAA Exchange study, 81.8% of drivers reported getting better fuel economy than the EPA estimates, while 16% reported lower fuel economy. The EPA adjusts its estimates to account for factors like ethanol blends, wind, hills, and road conditions.
