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UNITED STATES ENVIRONMENTA L PROTECTION AGENCY 

NATIONAL VEHICLE AND FUEL EMISSIONS LABORATORY 

2565 PLYMOUTH ROAD 

ANN ARBOR, MICHIGAN 48105-2498 

OFFICE OF 

AIR AND RADIATION

May 18, 2011 

MEMORANDUM

SUBJECT: Adjusting Combined City/Highway CAFE Fleet Values to Determine 

Equivalent 5-Cycle Label Values 

FROM: Roberts W. French, Jr. 

 Environmental Protection Specialist 

 Office of Transportation and Air Quality 

 U.S. Environmental Protection Agency 

TO: U.S. Environmental Protection Agency 

 Docket No. EPA-HQ-OAR-2009-0865 

As explained in the preamble to the final rule, our methodology for creating a ranking 

system for fuel economy and greenhouse gases depends on selecting an appropriate 

mid-point representing the fuel economy of the average vehicle. Given that Corporate 

Average Fuel Economy (CAFE) and greenhouse gas emission standards are programs 

with fleet average standards, these programs will essentially be determining the fuel 

economy of the average vehicle in any given model year for which there are standards. 

Consequently, given a rating system based on MPG, we chose to use the CAFE 

program to define the average vehicle, and from that vehicle we determined the MPG 

“bins” that define the 1 to 10 rating system. 

The EPA/NHTSA rulemaking that put greenhouse gas and CAFE standards in place for 

the 2012 through 2016 model years established the following fleet values (see 75 FR 

25331, May 7, 2010). It is these numbers, shown in the following table, that form the 

basis for our rating system, but with some adjustment. 
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Model

Year CAFE

2012 28.7

2013 29.7

2014 30.6

2015 31.5

2016 32.7

The CAFE standards and the label values are determined in different ways. Congress 

recognized the importance of maintaining a stable method for compliance with 

standards and essentially fixed the test methods for CAFE such that the test results 

don’t change over time. However, Congress has also recognized that the label values 

need to reflect real-world performance, and now requires EPA to periodically evaluate 

how well the label test and calculation methods are reproducing real-world experience. 

This memorandum details the method used to derive label values (sometimes called “5-

cycle” values) from the CAFE values above (sometimes called “2-cycle” values). 

In 2006 EPA promulgated a rule that established new test and calculation methods that 

took effect with the 2008 model year. The new method does not apply a flat, linear 

adjustment in the way that the previous method did. The new method applies a higher 

proportional adjustment to high fuel economy values than to low fuel economy values. 

Thus, although the difference could be subtle, the adjustment to the 2012 model year 

CAFE value of 28.7 MPG will be different than the adjustment applied to the 2016 value 

of 32.7. 

One other minor issue is that the CAFE values above are Combined City/Highway 

values, whereas the label values are adjusted separately by test cycle, i.e., the City 

value is adjusted using one formula, the Highway by another, and the Combined value 

determined from the adjusted City and Highway values. Because the CAFE values are 

fleet average standards based on the Combined City/Highway MPG, there are no 

separate specific City and Highway values to use to determine the real-world label 

value, as we would do for an individual vehicle. If such fleet City and Highway values 

existed we would simply adjust these by the existing methods to get our desired label 

values corresponding to the above CAFE values. 

To estimate Combined City/Highway label values that correspond to the above CAFE 

values, we used fuel economy data from the 2011 model year. The data includes City, 

Highway, and Combined in unadjusted (i.e., 2-cycle values comparable to CAFE) and 

adjusted (i.e., 5-cycle label values). We simply regressed the unadjusted Combined 

MPG values against the adjusted Combined values to determine an approximate 

relationship between the two. The data and the regression equation are shown in the 

following figure. 
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As noted earlier, the existing method to adjust test results to get to label values is nonlinear, thus a simple linear regression such as this should not be used for exacting 

purposes. For our purposes here, however, this approach is a sufficient way to 

translate each of the CAFE values to average label values, rounded to a whole MPG. 

For example, in the 2012 model year when the fleet is required to meet a CAFE 

standard of 28.7 MPG, we would expect, based on the method in this memorandum, 

that the similarly sales-weighted average of the label values across the fleet would be 

22 MPG. Thus the values in the “Label Average” column below are used to define the 

center of the rating system for these model years. The rating system for future model 

years will be addressed as CAFE standards for future years become known. 

Model

Year CAFE

Label

Average

2012 28.7 22

2013 29.7 23

2014 30.6 23

2015 31.5 24

2016 32.7 25

y = 0.7087x + 1.5581

0

10

20

30

40

50

60

0 10 20 30 40 50 60 70 80

Adjusted 5‐Cycle Combined MPG

Unadjusted 2‐Cycle Combined MPG