1 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-Cycl e Label Values

FROM : Roberts W. French, Jr. Environmental Protection Specialist Office of Transportation and Air Quality

U.S. Environment al Protection Agency

TO : U.S. Environment al Protection Agency
Docket No. EPA-HQ-OAR-2009-0865

As explained in the preamble to the final rule, our methodology fo r creating a ranking system for fuel economy and greenhouse ga ses depends on selecting an appropriate mid-point representing the fuel economy of the average vehicl e. Given that Corporate Average Fuel Economy (CAFE) and greenhous e gas emission standards are programs with fleet average standards, t hese 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 ve hicle we determined the MPG

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

The EPA/NHTSA rulemaking that put greenhous e 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 followin g table, that form the basis for our rating system, but with some adjustment.2 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 ar e determined in different ways. Congress recognized the importance of maintaini ng a stable method for compliance with standards and essentially fixed t he test methods for CAFE su ch 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 (s ometimes called “5- cycle” values) from the CAFE values above (sometimes called “2-cycle” values).

In 2006 EPA promulgated a rule that estab lished new test and calculation methods that took effect with the 2008 model year. T he new method does not apply a flat, linear adjustment in the way that the previous me thod 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 th an the adjustment applied to the 2016 value

of 32.7.

One other minor issue is that the CAFE va lues above are Comb ined City/Highway values, whereas the label values are adjust ed separately by test cycle, i.e., the City value is adjusted using one formula, the Hi ghway 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 Comb ined 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 vehi cle. If such fleet City and Highway values existed we would simply adjust these by t he 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 m odel 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 Combin ed values to determine an approximate relationship between the two. The data and the regression equation are shown in the following figure.3 As noted earlier, the existing method to adjust te st results to get to label values is nonlinear, thus a simple linear regression su ch 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 av erage 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, bas ed on the method in this memorandum, that the similarly sales-wei ghted average of the label values across the fleet would be

22 MPG. Thus the values in the “Label Av erage” column below are used to define the center of the rating system fo r 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 80Adjusted5‐CycleCombinedMPG

Unadjusted 2

‐ Cycle Combined MPG