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Light-Duty Vehicle CO2 and Fuel Economy Trends

About the CO2 and Fuel Economy Trends Data

Understanding the Trends Database

The Trends database has been maintained by EPA since 1975, and is the most comprehensive of its kind. Data for new vehicles produced for the U.S. fleet are submitted to the EPA and NHTSA at the conclusion of the model year and include actual production data and the results of emission and fuel economy testing performed by the manufacturers and EPA. The report covers all passenger cars, sport utility vehicles, minivans, and all but the largest pickup trucks and vans.

Data for model years (MY) 1975 through 2016 are final. Data for MY 2016 are preliminary and based on projected production data provided to EPA by automakers for vehicle certification and labeling prior to MY 2017 sales. MY 2017 values will be finalized in next year’s report. All data are based on production volumes delivered for sale in the U.S. by model year, and may vary from publicized data based on calendar year sales. Most of the data are reported as fleetwide averages, reflecting arithmetic production-weighted averages of individual CO2 emissions values and harmonic production-weighted averages of individual fuel economy values.

Data from alternative fuel vehicles (AFVs) are integrated into the overall database, beginning with MY 2011 data. These vehicles include electric vehicles, plug-in hybrids, fuel cell vehicles, and compressed natural gas vehicles. CO2 emissions from alternative fuel vehicles represent tailpipe emissions, while fuel economy for alternative fuel vehicles is reported as mpge (miles per gallon of gasoline equivalent), or the miles an alternative fuel vehicle can travel on an amount of energy equivalent to that in a gallon of gasoline.

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About Fuel Economy and CO2 Values

The primary CO2 and fuel economy data in the Trends report are adjusted values that represent EPA’s best estimates of real world performance. The adjusted data for this report are based on the same underlying data submitted to EPA for the both the consumer Label and the CAFE and GHG compliance programs, but there are some important differences.

Unadjusted, laboratory values are used to determine automaker compliance with the standards, along with various regulatory incentives and credits. These values are measured with EPA’s City and Highway Test procedures (the “2-cycle” tests). A combined city/ highway value is then calculated using a 55%/45% city-highway weighted average. These unadjusted, laboratory values do not fully represent real world driving, but are occasionally presented in this report because they provide a consistent baseline for comparing trends in vehicle design over time.

The consumer data reported on the EPA/DOT Fuel Economy and Environment Labels (“window stickers”) use a more realistic “5-cycle” test procedure intended to better reflect real world performance. The combined city/highway Label values use the 55%/45% city-highway weighting. The adjusted values in the Trends report are also derived from 5-cycle test values, but use a city-highway weighting of 43%/57% consistent with fleetwide driver activity data.

CO2 and Fuel Economy Data Type Purpose City/Highway Weighting Test Basis
Adjusted Best estimate of real world performance 43% / 57% 5-cycle
Label Consumer information to compare individual vehicles 55% / 45% 5-cycle
Unadjusted, Laboratory Basis for automaker compliance with standards 55% / 45% 2-cycle

Adjusted CO2 emissions values are, on average, about 25% higher than unadjusted CO2 values, and adjusted fuel economy values are about 20% lower than unadjusted fuel economy values.

Since major methodological changes are generally propagated backwards through the historical database in order to maintain the integrity of long-term trends, this report supersedes previous versions in the series and should not be compared to past reports.

For additional trends database details and methodological explanation of fuel economy and CO2 values and calculations throughout the historical database, see Section 10 of the Full Trends Report.

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