TRS Question of The Month: How are conventional light-duty vehicle fuel economy ratings determined and reported?
It’s important to understand the who, what, when, where, and why (and how!) of fuel economy testing and labeling. In particular, you may be interested in the recent changes described below (see “When” section).
“Who” is tested?
Most light-duty vehicles must be tested for fuel economy. Exceptions include motorcycles, pickup trucks and cargo vans with a gross vehicle weight rating (GVWR) above 8,500 lbs., and passenger vehicles with a GVWR above 10,000 lbs..
Original equipment manufacturers (OEMs) test a representative vehicle for each light-duty model and report the results to the U.S. Environmental Protection Agency (EPA). The EPA reviews the results and confirms estimates for about 10% to 15% of the vehicles through tests at the National Vehicles and Fuel Emissions Laboratory (NVFEL).
How are vehicles tested?
Vehicles are tested in a laboratory using a standardized procedure established by the EPA. The vehicle’s drive wheels are placed on a machine called a dynamometer that simulates the driving environment—much like an exercise bike simulates cycling. The energy required to move the rollers is adjusted to account for wind resistance and the vehicle’s weight. On the dynamometer, a professional driver runs the vehicle through standardized driving routines, which simulate “typical” trips in the city or on the highway. Each driving routine specifies the speed the vehicle must travel during each second in the test. To measure the fuel economy of the vehicle, a hose is connected to the tailpipe to collect the engine exhaust during the tests. The carbon in the exhaust is measured to calculate the amount of fuel burned.
From there, the manufacturer enters the test results into an equation the EPA has established to determine the final city and highway fuel economy estimates (see the Code of Federal Regulations, 40 CFR 600.210-12). Combined city/highway fuel economy is calculated by weighting the city miles per gallon (mpg) value by 55% and the highway value by 45%. Combined fuel economy values provide consumers with a quick and easy comparison point across vehicles.
What information is included on the fuel economy label?
In addition to providing city, highway, and combined city/highway mpg fuel economy estimates, the new fuel economy label provides information about emissions and fuel cost:
- Comparing fuel economy to other vehicles: The label shows the average mpg rating of similar sized vehicles for users to easily compare fuel economy. It also estimates how much money you would save or spend in fuel costs over five years compared to the average vehicle.
- Annual fuel cost: Based on annual mileage assumptions, projected fuel price, and mpg rating, the label displays estimated annual fuel cost.
- Emissions information: The label rates the vehicle on a scale from 1 to 10 for (a) fuel economy and greenhouse gas and (b) smog emissions, making it easier for consumers to choose cleaner vehicles.
- QR Code: Users are able to scan the QR Code on the label to access helpful tools and additional information about the vehicle’s fuel economy and emissions.
When did this rating system come into effect?
The EPA’s fuel economy testing and labeling procedures were initially established in the late 1970s and have evolved over time. The EPA updated its fuel economy methodology with MY 2008 vehicles and again this year with MY 2017 vehicles. The 2008 methodology changes incorporated the effects of faster speeds and acceleration, air conditioner use, and colder outside temperatures. These updated methods improved the accuracy of fuel economy estimates.
This year’s changes are more subtle. As described in the “How” section above, the EPA is responsible for providing an equation that manufacturers use to calculate the final city and highway fuel economy for their vehicles. Starting with MY 2017 vehicles, the EPA updated the equations used to calculate fuel economy estimates for some vehicles. The updated equations better reflect the more fuel-efficient vehicles and advanced technologies (e.g., hybrids and tubocharged engines) on the road today. While most vehicles will not be affected, some fuel economy estimates will decrease by 1 to 2 mpg.
MY 2011–2016 mpg estimates on FuelEconomy.gov have been converted to the new ratings system to allow for easier comparison of fuel economy of newer and older cars. For more information, see the FuelEconomy.gov Compare MPG tool.
Where is fuel economy data available?
EPA fuel economy estimates are displayed on the Fuel Economy and Environment stickers affixed to the window of new vehicles. Fuel economy estimates for vehicles from model year 1984 to present are also available online at DOE’s FuelEconomy.gov website. FuelEconomy.gov’s Find a Car tool allows users to search by vehicle make, model, and year. The website’s My MPG page allows consumers to calculate, track, and post their fuel economy to compare it with the EPA test ratings and other users’ posted results. Full fuel economy data is downloadable in PDF or spreadsheet form on FuelEconomy.gov.
Why does this matter?
Accurate and detailed fuel economy information allows consumers to make informed decisions. Widely available and clearly presented data supports the purchases of clean and efficient vehicles. As always, it is important to remember that the EPA ratings are a useful tool for comparing vehicles because they are always done the same way under the same set of conditions. However, since consumer driving conditions and styles can vary greatly, the fuel economy some drivers achieve may vary from the EPA’s estimates. For tips on improving your fuel economy, visit the Factors that Affect Fuel Economy page on FuelEconomy.gov.
Watch for more information next month on how fuel economy for bi-fuel vehicles, including plug-in hybrid electric vehicles, is tested and reported.
- Clean Cities Technical Response Service Team