UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

NATIONAL VEHICLE AND FUEL EMISSIONS LABORATORY

2565 PLYMOUTH ROAD

ANN ARBOR, MICHIGAN 48105-2498

 OFFICE OF

AIR AND RADIATION

February 27, 2012

CD-12-03 (LDV/LDT/ICI/LIMO)

SUBJECT: Analytically Derived CO2 and Carbon-Related Exhaust Emissions 

(CREE) for Light-Duty Vehicles

Dear Manufacturer:

The enclosed letter to the Alliance of Automobile Manufacturers (AAM) is provided for 

your information as we believe it is of general interest to all manufacturers. This guidance 

outlines a method of calculating analytically derived CO2 and CREE values for light-duty 

vehicles based on the analytically-derived fuel economy (ADFE) of the vehicle 

subconfiguration, ref. EPA guidance letter CCD-04-06, March 11, 2004.

Regulatory Background – The basis for determining analytically derived fuel economy, 

CO2 and CREE values is outlined in the provisions of 40 CFR 600.006(e), which read in 

part:

“.....Additionally, in lieu of submitting actual data from a test vehicle, a 

manufacturer may provide fuel economy, CO2 emissions, and carbon-related 

exhaust emission values derived from an analytical expression, e.g., regression 

analysis. In order for fuel economy, CO2 emissions, and carbon-related exhaust 

emission values derived from analytical methods to be accepted, the expression 

(form and coefficients) must have been approved by the Administrator.” 

Also enclosed are the August 8 and November 25, 2011 letters from AAM requesting 

approval of their proposed calculation method. 

If you have questions about this letter, please contact Dave Good via email at 

good.david@epa.gov (telephone 734-214-4450) or your certification team representative.

Sincerely,

Byron J Bunker, Acting Director

Compliance Division

Office of Transportation and Air Quality

Enclosures
UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

NATIONAL VEHICLE AND FUEL EMISSIONS LABORATORY

2565 PLYMOUTH ROAD

ANN ARBOR, MICHIGAN 48105-2498

 OFFICE OF

AIR AND RADIATION

February 23, 2012

Giedrius Ambrozaitis

Alliance of Automobile Manufacturers

2000 Town Center, Suite 1140

Southfield, MI 48075

Dear Mr. Ambrozaitis:

This letter responds to your August 8 and November 25, 2011 letters requesting approval of 

your proposed method to calculate analytically derived Carbon Related Exhaust Emissions 

(ADCREE or ADOCREE1) and analytically derived CO2 (ADCO2). Your letters propose 

to calculate ADCREE, ADOCREE and ADCO2 at the test vehicle level2 as follows:

ADCREE & ADCO2 = Fuel Conversion Factor / ADFE

ADOCREE = (Fuel Conversion Factor / ADFE) + 298 x N2O + [25 – (CWF/0.273)] x CH4

Where:

ADCREE = analytically derived CREE;

ADOCREE = analytically derived Optional CREE where CH4 and N2O emissions 

are included in the CREE equation, ref. 40 CFR 86.1818(f)(2);

ADCO2 = analytically derived CO2 emissions in grams/mile;

ADFE = analytically derived fuel economy calculated according to the method 

outlined in EPA guidance letter CCD-04-06, March 11, 2004; 

N2O = N2O emissions in grams/mile

CH4 = CH4 emissions in grams/mile

CWF = Carbon weight factor of the test fuel; ref. 40 CFR 600.113-12(f)(1)(ii);

Fuel Conversion Factors:

• Gasoline test fuel: 8887 grams/gallon

• Diesel test fuel: 10,180 grams/gallon

• Ethanol (E85) test fuel: 6295 grams/gallon

• California Phase II test fuel: 8730 grams/gallon

 1 ADCREE means analytically derived CREE. ADOCREE means analytically derived Optional CREE 

where CH4 and N2O emissions are included in the CREE equation, ref. 40 CFR 86.1818(f)(2).

2 When used in fleet average calculations, ADCREE and ADOCREE values are full useful life terms which 

must include applicable deterioration factors or be obtained from test vehicles equipped with aged emission 

control system components, ref. 40 CFR 600.113-12(g)(2).
EPA staff has reviewed the technical merits of your proposal and concur with your 

proposed methodology. The basis for our concurrence includes the following:

• Your proposed methodology is consistent with the methodology used to derive 

analytically derived fuel economy (ADFE) for light-duty vehicles, ref. EPA 

guidance letter CCD-04-06, March 11, 2004.

• Since your proposed methodology is based on the ADFE of a vehicle, it inherently 

incorporates the 95% confidence limits (used to determine ADFE of the vehicle) 

into the analytically derived CREE, OCREE and CO2 equations for the vehicle.

• Your proposal uses fuel conversion factors for gasoline, diesel fuel and ethanol 

(E85) test fuel which have been previously accepted by EPA, ref. light-duty 

greenhouse gas final rule (75 FR 25324 May 7, 2010); heavy-duty greenhouse gas 

final rule (76 FR 37106, Sept. 15, 2011); and SmartWay document “Guidance for 

Implementing Section 141 of the Energy Independence and Security Act of 2007,” 

Table 1 on page 3, available at 

http://www.epa.gov/greenvehicles/download/420B10008.pdf.

• Your proposal uses fuel conversion factors for California Phase II test fuel based on 

fuel properties of five batches of manufacturer test fuel. Those fuel properties are 

consistent with fuel properties of EPA Phase II test fuel. In addition, your proposed 

fuel conversion factor is similar to one developed for Phase II test fuel by the 

California Air Resources Board (ref. Oct 19, 2011 email message from Paul 

Hughes, ARB to Dave Good, EPA). 

Therefore, based on the provisions of 40 CFR 40 CFR 600.006(e) as revised in the 2013 FE 

Label final rule (76 FR 39528, July 6, 2011), we hereby approve the use of your proposed 

calculation method. Our approval is effective immediately and is applicable to model year 

2009 and later analytically derived data for light-duty vehicles (passenger cars), light-duty 

trucks and medium-duty passenger vehicles (MDPVs). The details and conditions of our 

approval are outlined in Enclosure I.

If you have questions about this letter, please contact Dave Good via email at 

good.david@epa.gov or at 734-214-4450.

Sincerely,

Linc Wehrly, Center Director

Light-Duty Vehicle Center

Compliance Division

Office of Transportation and Air Quality

Enclosure
Analytically Derived CREE/CO2 Guidelines

Without prior EPA approval, manufacturers may select the baseline test to be used for 

analytically derived fuel economy (ADFE), analytically derived CREE (ADCREE), 

analytically derived optional CREE (ADOCREE) and analytically derived CO2

(ADCO2), provided the following guidelines are followed:

1. The ADFE used in the ADCREE, ADOCREE and ADCO2 equations must be 

determined using the method outlined in EPA guidance letter CCD-04-06, March 11, 

2004 (or any subsequent updates to that guidance letter). All conditions outlined in 

Enclosure 1 of CCD-04-06 must be satisfied.

2. ADCREE, ADOCREE and ADCO2 may be used to calculate FTP (city), highway, 

US06, SC03 and cold temperature FTP tests, provided that ADFE is calculated for 

US06, SC03 and cold temperature FTP tests according to the guidelines provided in 

Section 6 of EPA guidance letter CISD-10-04, February 22, 2010.

3. If the fuel economy of a vehicle subconfiguration is based on ADFE, the CREE and 

CO2 values for that vehicle subconfiguration must also be based on applicable 

ADCREE, ADOCREE and ADCO2 calculations, (and visa-versa).

4. When used in fleet average calculations, ADCREE and ADOCREE are full-useful 

life terms which must include applicable deterioration factors or be obtained from test 

vehicles equipped with aged emission control system components, ref. 40 CFR 

600.113-12(g)(2).

5. ADCREE, ADOCREE and ADCO2 values cannot be used for the emission data 

vehicle.

6. Vehicles considered for selection for the baseline test for ADFE must pass applicable 

N2O and CH4 emission standards, ref EPA guidance letter CISD-04-06, Enclosure 1, 

item 1.a. If the manufacturer didn’t measure N2O or CH4 emissions, the manufacturer 

shall base compliance on their good engineering judgment.

7. To limit the impact of ADCREE or ADOCREE on fleet average CREE calculations, no more 

than 20 percent of the subconfigurations tested in a manufacturer’s greenhouse gas final fleet 

average model year report may be represented by ADCREE or ADOCREE. For example, 

if the manufacturer has 100 subconfigurations which are tested (or represented through data 

substitutions and equivalencies) only 20 of the 100 may be based on ADCREE or ADOCREE

calculations (or represented through data substitutions or equivalencies from ADCREE or 

ADOCREE generated data points).

8. Manufacturers must retain for five years (under the provisions of 40 CFR 600.005(a)(3) the 

pool of tests, the vehicle description and tests chosen for the ADCREE/ADOCREE/ADCO2

subconfiguration and the calculated ADCREE/ADOCREE/ADCO2 values. EPA may request 

this information as part of an audit.

9. If EPA determines that it is necessary to assure the integrity of the emissions and fuel 
economy database or if EPA has concerns about compliance with emission standards, EPA 

retains the right to order a confirmatory test of the subconfiguration covered by the 

ADCREE/ADOCREE/ADCO2.

For labeling purposes, if the manufacturer chooses, EPA will accept a temporary Fuel 

Economy Label based on the manufacturer’s ADCO2 data while a suitable data vehicle is 

being procured. However, if the confirmatory test value results in higher CO2 value for 

any model type, the label must be updated. The updated label value shall be used on all 

vehicles produced more than 15 days following its submission.

10. EPA is presenting this option as a manufacturer self-approval process. EPA will not be

responding to routine submissions of ADCREE/ADOCREE/ADCO2 data indicating our 

acceptance of the calculation or waiver of confirmatory testing. If EPA later discovers that 

the procedures for self-approval were not followed, EPA may rescind the use of 

ADCREE/ADOCREE/ADCO2 data and require actual test data be generated and require 

recalculation of label values and greenhouse gas final fleet average model year reports. 
BMW Group • Chrysler Group LLC • Ford Motor Company • General Motors Company • Jaguar Land Rover 

Mazda • Mercedes-Benz USA • Mitsubishi Motors • Porsche • Toyota • Volkswagen • Volvo 

 

2000 Town Center—Suite 1140, Southfield, MI 48075 • Phone 248.357.4717 • Fax 248.357.4740 • www.autoalliance.org

August 8, 2011 

David Good 

U.S. Environmental Protection Agency 

Office of Transportation and Air Quality 

2000 Traverwood Drive 

Ann Arbor, MI 48105 

Re: Request for Approval of Analytically Derived Carbon Related Exhaust Emission and 

Carbon Dioxide Factors 

Dear Mr. Good: 

This is to follow-up to our June 15, 2011, email which proposed that EPA approve the use of 

factors to convert analytically derived fuel economy (ADFE) values to carbon related exhaust 

emission (CREE) and carbon dioxide (CO2) emission values. Specifically, this letter submits the 

additional information you requested regarding the proposal.

On March 11, 2004, EPA published a Dear Manufacturer guidance letter (CCD-04-06) which 

updated the well established ADFE policy for 2005 MY and newer vehicles (please see the 

March 2004 letter for a comprehensive listing of all historical ADFE guidances starting in the 

1980’s). The March 2004 guidance letter updated the existing ADFE equation coefficients using 

a statistical analysis of 3642 EPA fuel economy tests of then recent vintage 2000-2004 MY 

vehicles (Enclosure 2 to the March 2004 guidance letter). An update to the coefficients was 

required at that time due to the change to single-roll dynamometers; the statistical analysis was 

developed using only single-roll dynamometer data. Because there have been no further major 

test procedure changes (such as a dynamometer change), the Alliance is proposing that both the 

ADFE coefficients and the ADFE formula contained in the March 2004 guidance continue to be 

used on current and future model year vehicles. 

The need to develop analytically derived CREE (ADCREE) comes from the implementation of 

the 2012-2016 greenhouse gas (GHG) rule which adopts a fleet-average CREE standard in terms 

of grams per mile (g/mi) and which requires that all test data that is used in CAFE calculations 

also be used in the calculation of fleet-average CREE. In order to accommodate the use of 

CAFE ADFE data in CREE space, it is necessary to develop a method to calculate analytically 
2 

derived CREE. The need to develop analytically derived CO2 (ADCO2) values comes from the 

new fuel economy label rule which requires a CO2 value to appear on the label. In order to 

accommodate the use of ADFE data in FE labels, it is now necessary to also develop a method to 

calculate analytically derived CO2. An appropriate and efficient method of deriving analytically 

derived CREE and CO2 values would be to divide a fuel conversion factor by the ADFE value. 

We are proposing to use the same fuel conversion factors in determining both ADCREE and 

ADCO2. 

The calculation method is as follows: 

Analytically Derived CREE & CO2 = Fuel Conversion factor / ADFE Value 

The Alliance proposes the following fuel conversion factors: 

• Gasoline : 8887 grams/gallon 

EPA and NHTSA determined that 8887 is the appropriate value and have used this value 

in calculations for the 2012-2016 GHG rule (see Light-Duty Vehicle Greenhouse Gas 

Emission Standards and Corporate Average Fuel Economy Standards; Final Rule, 75 

Fed. Reg. 25330, f.n. 20 (May 7, 2010)). 

• Diesel : 10180 grams/gallon 

EPA and NHTSA determined that 10180 is the appropriate value and have used this 

value in calculations for the 2012-2016 GHG rule (see footnote 20, cited above). 

• E85: 6262 grams/gallon 

This is the average value from a statistical analysis of E85 fuel properties from actual test 

fuels used by manufacturers. (See Attachment for this statistical analysis.) 

• California RFG2: 8730 grams/gallon 

This is the average value from a statistical analysis of RFG2 fuel properties from actual 

test fuels used by manufacturers. (See Attachment for this statistical analysis.) 

 

Regarding your question about the applicability of the heavy-duty (HD) vehicle approach to 

analytically derived CREE and also to light-duty (LD), we believe that EPA’s HD GHG NPRM 

(75 Fed. Reg. 74262 (November 30, 2010)) actually proposed that HD adopt the LD approach, 

but with a greater fraction of possible subconfigurations and using lower confidence limits. As 

we noted above, the Alliance is not proposing any changes to the existing March 2004 LD 

guidance and therefore the HD approach is not applicable to LD and HD should be treated 

separately from LD. 
3 

In summary, the Alliance requests that EPA approve the use of the above factors for converting 

ADFE values to ADCREE and ADCO2 values and release this information via a new Dear 

Manufacturer guidance letter. Please let me know if I can answer any further questions. 

Best regards, 

 

Giedrius Ambrozaitis 

Alliance of Automobile Manufacturers 

(248) 915-8836 

cc: Linc Wehrly, US EPA 

Attachment - Statistical Analysis of E85 and RFG2 Fuel Properties 
Alliance of Automobile Manufacturers

Attachment to ADCREE Letter to EPA - August 8, 2011

Carbon Balance Equation for Diesel (40 CFR 600 113 12(i)(1)):

"Carbon Balance Equation" for Federal Tier 2 (FAT2) Gasoline (40 CFR 600.113-12(h)(1)):

mpg = (51740000*CWF*SG)/(((CWF*HC)+(0.429*CO)+(0.273*CO2))*((0.6*SG*NHV)+5471))

Solving for CO2:

CO2 = ((51740000*CWF*SG)/(0.273*((0.6*SG*NHV)+5471)*mpg)) - ((CWF*HC)/0.273) - ((0.429*CO)/0.273)

Ignoring minimal contribution from HC and CO:

CO2*mpg = (51740000*CWF*SG)/((0.1638*SG*NHV)+1493.583)

"Carbon Balance Equation" for E85 (ED85) (40 CFR 600.113(l)(1)):

mpg = (3781.8*CWF*SG)/((CWF*HC)+(0.429*CO)+(0.273*CO2)+(0.375*CH3OH)+(0.400*HCHO)+(0.521*C2H5OH)+(0.545*C2H4O)

Solving for CO2:

CO2 = ((3781.8*CWF*SG)/(0.273*mpg))-((CWF*HC)+(0.429*CO)+(0.375*CH3OH)+(0.400*HCHO)+(0.521*C2H5OH)+(0.545*C2H4O))/0.273

Ignoring minimal contribution from HC,CO, CH3OH, HCHO, C2H5OH and C2H4O:

CO2*mpg = (3781.8*CWF*SG)/0.273

"Carbon Balance Equation" for California Phase 2 (PHS2) Gasoline (EPA Letter CD-95-09):

mpg = (51740000*CWF*SG)/(((1.03*CWF*HC)+(0.429*CO)+(0.273*CO2))*((0.6*SG*NHV)+5471))

Solving for CO2:

CO2 = ((51740000*CWF*SG)/(0.273*((0.6*SG*NHV)+5471)*mpg)) - ((1.03*CWF*HC)/0.273) - ((0.429*CO)/0.273)

Ignoring minimal contribution from HC and CO:

CO2*mpg = (51740000*CWF*SG)/((0.1638*SG*NHV)+1493.583)

"Carbon . Balance Equation" for Diesel (40 CFR 600.113-12(i)(1)):

mpg = 2778/((.866*HC)+(0.429*CO)+(0.273*CO2))

Solving for CO2:

CO2 = (10176/mpg) - (3.17*HC) - (1.57*CO)

Ignoring minimal contribution from HC and CO:

CO2*mpg = 10176

Fuel Type

Net 

Heating 

Value 

(NHV)

Carbon 

Weight 

Fraction 

(CWF)

Specific 

Gravity 

(SG)

CO2*MPG 

(gm/gal)

Based on 9 batches of E85:

Average ED85 12636.44 0.576867 0.783556 6261.539856

High 6329

Low 6185

Based on 5 batches of CA Phase 2 fuel:

Average PHS2 18144.4 0.843 0.7378 8729.602988

High 8756

Low 8708
BMW Group • Chrysler Group LLC • Ford Motor Company • General Motors Company • Jaguar Land Rover 

Mazda • Mercedes-Benz USA • Mitsubishi Motors • Porsche • Toyota • Volkswagen • Volvo

 

2000 Town Center—Suite 1140, Southfield, MI 48075 • Phone 248.357.4717 • Fax 248.357.4740 • www.autoalliance.org

November 25, 2011

David Good

U.S. Environmental Protection Agency

Office of Transportation and Air Quality

2000 Traverwood Drive

Ann Arbor, MI 48105

Re: Revised Request for Approval of Analytically Derived Carbon Related Exhaust 

Emission and Carbon Dioxide Factors

Dear Mr. Good:

This letter is a revised request to EPA for the use of conversion factors to convert analytically 

derived fuel economy (ADFE) to carbon related exhaust emissions (ADCREE), optional carbon 

related exhaust emissions (ADOCREE) and carbon dioxide (ADCO2). The Alliance requests that 

EPA approve the use of the factors for converting ADFE values to ADCREE, ADOCREE and 

ADCO2 and the associated agreements described in the August 8, 2011 letter and this revised 

request. We also request that EPA release this information via a new Dear Manufacturer 

guidance letter,

Attached is the original Alliance request letter from August 8, 2011, with the analysis of fuel 

properties attachment. As part of this revised request, the Alliance requests the following 

revisions:

1. The Alliance agrees that the equation on page two of the August 8, 2011, letter should 

include ADOCREE (optional CREE) where CH4 and N2O are included in the CREE 

equation as outlined in 86.1818(f)(2)). We propose the following equation to calculate the 

Analytically Derived OCREE (ADOCREE) more accurately for all fuels.

ADOCREE = (Fuel Conversion Factor / ADFE) + 298 x N2O + [25-(CWF/0.273)] x CH4

The justification of using the above equation for all fuels is as follows (Gasoline 

Example):

OCREE= [(CWF/0.273)×NMHC] + 1.571×CO + CO2 + 298×N2O + 25×CH4
2

= [(CWF/0.273)×NMHC] + 1.571×CO + CO2 + 298×N2O + 25×CH4 + 

(CWF/0.273)×CH4 - (CWF/0.273)×CH4; (CWF/0.273) x CH4 added and subtracted at 

the same time (no effect on the above equation)

= [(CWF/0.273)×NMHC] + (CWF/0.273)×CH4 + 1.571×CO + CO2 + 298×N2O + 

25×CH4 - (CWF/0.273)×CH4

= [(CWF/0.273)×(NMHC+CH4)] + 1.571×CO + CO2 + 298 × N2O + [25 -(CWF/0.273)] 

× CH4

= [(CWF/0.273)×HC] + 1.571×CO + CO2 + 298 × N2O + [25 - (CWF/0.273)] × CH4

= CREE + 298 × N2O + [25 - (CWF/0.273)] × CH4

ADOCREE = ADCREE + 298 × N2O + [25 - (CWF/0.273)] × CH4

OR 

(If ADFE is used to calculate ADCREE then all components of hydrocarbons are

included in the FE number and this equation becomes useful for all fuels)

ADOCREE= (Fuel Conversion Factor / ADFE) + 298 × N2O + [25 - (CWF/0.273)] × 

CH4

2. Regarding EPA’s concern about demonstrating compliance with applicable N2O and 

CH4 emission standards, one of the conditions to use ADFE is that ”Vehicles considered 

for selection for the baseline test must pass all applicable emission standards in the model 

year associated with the ADFE.” ref. EPA guidance letter CISD-04-06, Enclosure 1, item 

1.a. The Alliance believes that as a prerequisite to the use of ADFE, manufacturers 

should treat N2O and CH4 compliance similarly to any other emission constituent. The 

only issue may be if the manufacturer did not collect N2O or CH4 data for the base test. 

If that is the case, the manufacturer should be able to use good engineering judgment in 

addressing compliance to N2O and CH4 emission standards.

3. The Alliance believes that current advanced technology vehicles fit under the existing 

ADFE guidelines and that the coefficients are applicable. If EPA believes that some 

future advanced technologies may not be a good fit, then the applicability of the guidance 

should be revisited at that time.

4. The Alliance agrees that the use of ADFE, ADCREE, ADOCREE and ADCO2 should be 

limited to light-duty vehicles (e.g. which are required to demonstrate compliance with 

light-duty greenhouse gas and 2013 FE Label requirements).

5. For the conversion factors, the Alliance now believes that the value used by EPA for E85 

SmartWay calculations is an applicable value for E85 fuel. Therefore the E85 value 

should be 6295 grams/gallon, instead of 6262 grams/gallon as in the Alliance fuels 
3

analysis attachment. The values for the other fuels remain as in the fuels analysis 

attachment. 

Sincerely,

Giedrius Ambrozaitis

Alliance of Automobile Manufacturers

(248) 915-8836

Attachment – Alliance August 8, 2011 request with fuels analysis attachment