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Title: Analysis of In-Use Fuel Economy Shortfall Based on Voluntarily Reported MPG Estimates

Abstract

The usefulness of the Environmental Protection Agency's (EPA) passenger car and light truck fuel economy estimates has been the subject of debate for the past three decades. For the labels on new vehicles and the fuel economy information given to the public, the EPA adjusts dynamometer test results downward by 10% for the city cycle and 22% for the highway cycle to better reflect real world driving conditions. These adjustment factors were developed in 1984 and their continued validity has repeatedly been questioned. In March of 2005 the U.S. Department of Energy (DOE) and EPA's fuel economy information website, www.fueleconomy.gov, began allowing users to voluntarily share fuel economy estimates. This paper presents an initial statistical analysis of more than 3,000 estimates submitted by website users. The analysis suggests two potentially important results: (1) adjusted, combined EPA fuel economy estimates appear to be approximately unbiased estimators of the average fuel economy consumers will experience in actual driving, and (2) the EPA estimates are highly imprecise predictors of any given individual's in-use fuel economy, an approximate 95% confidence interval being +/-7 MPG. These results imply that what is needed is not less biased adjustment factors for the EPA estimates but rather moremore » precise methods of predicting the fuel economy individual consumers will achieve in their own driving.« less

Authors:
 [1];  [1];  [2];  [1]
  1. ORNL
  2. University of Tennessee, Knoxville (UTK)
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org.:
USDOE Office of Energy Efficiency and Renewable Energy (EERE)
OSTI Identifier:
931042
DOE Contract Number:
DE-AC05-00OR22725
Resource Type:
Conference
Resource Relation:
Conference: Transportation Research Board's Annual Meeting, Washington, DC, USA, 20060122, 20060126
Country of Publication:
United States
Language:
English
Subject:
32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATION; AUTOMOBILES; DYNAMOMETERS; FUEL CONSUMPTION; TRUCKS; US EPA; DATA ANALYSIS

Citation Formats

Greene, David L, Goeltz, Rick, Hopson, Dr Janet L, and Tworek, Elzbieta. Analysis of In-Use Fuel Economy Shortfall Based on Voluntarily Reported MPG Estimates. United States: N. p., 2007. Web.
Greene, David L, Goeltz, Rick, Hopson, Dr Janet L, & Tworek, Elzbieta. Analysis of In-Use Fuel Economy Shortfall Based on Voluntarily Reported MPG Estimates. United States.
Greene, David L, Goeltz, Rick, Hopson, Dr Janet L, and Tworek, Elzbieta. Mon . "Analysis of In-Use Fuel Economy Shortfall Based on Voluntarily Reported MPG Estimates". United States. doi:.
@article{osti_931042,
title = {Analysis of In-Use Fuel Economy Shortfall Based on Voluntarily Reported MPG Estimates},
author = {Greene, David L and Goeltz, Rick and Hopson, Dr Janet L and Tworek, Elzbieta},
abstractNote = {The usefulness of the Environmental Protection Agency's (EPA) passenger car and light truck fuel economy estimates has been the subject of debate for the past three decades. For the labels on new vehicles and the fuel economy information given to the public, the EPA adjusts dynamometer test results downward by 10% for the city cycle and 22% for the highway cycle to better reflect real world driving conditions. These adjustment factors were developed in 1984 and their continued validity has repeatedly been questioned. In March of 2005 the U.S. Department of Energy (DOE) and EPA's fuel economy information website, www.fueleconomy.gov, began allowing users to voluntarily share fuel economy estimates. This paper presents an initial statistical analysis of more than 3,000 estimates submitted by website users. The analysis suggests two potentially important results: (1) adjusted, combined EPA fuel economy estimates appear to be approximately unbiased estimators of the average fuel economy consumers will experience in actual driving, and (2) the EPA estimates are highly imprecise predictors of any given individual's in-use fuel economy, an approximate 95% confidence interval being +/-7 MPG. These results imply that what is needed is not less biased adjustment factors for the EPA estimates but rather more precise methods of predicting the fuel economy individual consumers will achieve in their own driving.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Mon Jan 01 00:00:00 EST 2007},
month = {Mon Jan 01 00:00:00 EST 2007}
}

Conference:
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  • The fuel consumption impacts of revised estimates of the shortfall between the EPA-measured and on-road fuel economy of light-duty vehicles (passenger cars and light-duty trucks less than 8500 lbs GVW) are examined. The analysis uses the DOE Highway Fuel Consumption model to project fuel demand. The technologies and technology-specific shortfall relations are examined. The procedure used to develop aggregate technology-weighted fuel economy shortfall relations for the Highway Fuel Consumption model is outlined. The fuel demand impacts of alternative assumptions regarding technology-specific shortfall are compared. (LEW)
  • Medium- and heavy-duty truck fuel economy and use characteristics as reported in the 1977 Truck Inventory and Use Survey (TIUS) are examined. The study focuses on in-use fuel economy, the use of fuel conservation equipment and annual miles per truck for three vehicle weight categories as functions of engine fuel type and area of operation. The TIUS data show that there is no significant difference between the average fuel economy of gasoline vs. diesel trucks in each of the three weight categories considered in the analysis. Significant differences are shown in annual miles per truck by weight category, fuel type,more » and area of operation. The data also illustrate a large increase in the use of fuel conservation equipment in both new and older trucks.« less
  • No abstract prepared.
  • A vehicle's in-use or on-the-road fuel economy often differs substantially from the miles-per-gallon estimates developed by the US Environmental Protection Agency (EPA) as part of its emissions certification program. As a result, the certification values are routinely adjusted by a set of correction factors so that the resulting estimates will better reflect in-use experience. Our analysis investigated how well the correction factors replicated the shortfall experience of all household vehicles on the road in 1985 and of those vehicles held by different population groups. Using data from the Residential Transportation Energy Consumption Survey conducted by the Energy Information Administration ofmore » the US Department of Energy, our analysis showed that fleetwide, the shortfall is larger than the EPA correction factors, and that light trucks are experiencing larger shortfalls than automobiles. Controlling for vehicle age and size class, shortfalls did not appear to differ by population group. However, African-American households appeared to select vehicles with systematically lower fuel economy (both EPA-test and on-the-road) within individual vehicle age and size class categories.« less
  • A vehicle`s in-use or on-the-road fuel economy often differs substantially from the miles-per-gallon estimates developed by the US Environmental Protection Agency (EPA) as part of its emissions certification program. As a result, the certification values are routinely adjusted by a set of correction factors so that the resulting estimates will better reflect in-use experience. Our analysis investigated how well the correction factors replicated the shortfall experience of all household vehicles on the road in 1985 and of those vehicles held by different population groups. Using data from the Residential Transportation Energy Consumption Survey conducted by the Energy Information Administration ofmore » the US Department of Energy, our analysis showed that fleetwide, the shortfall is larger than the EPA correction factors, and that light trucks are experiencing larger shortfalls than automobiles. Controlling for vehicle age and size class, shortfalls did not appear to differ by population group. However, African-American households appeared to select vehicles with systematically lower fuel economy (both EPA-test and on-the-road) within individual vehicle age and size class categories.« less