UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

NATIONAL VEHICLE AND FUEL EMISSIONS LABORATORY

2565 PLYMOUTH ROAD

ANN ARBOR, MI 48105-2498

 OFFICE OF

 AIR AND RADIATION

July 16, 2015

MEMORANDUM

SUBJECT: Example CO2 Emissions Calculations for Box Trailers

FROM: Jessica Brakora, Engineer, Assessment and Standards Division

TO: Greenhouse Gas Emissions Standards and Fuel Efficiency Standards for Medium- and 

Heavy-Duty Engines and Vehicles - Phase 2 - Docket EPA-HQ-OAR-2014-0827

Introduction

Attached is a Microsoft Excel spreadsheet that can be used to estimate the CO2 emissions from box 

trailers, while considering production volumes and potential averaging. The calculations in this 

spreadsheet use the GEM-based equation constants derived from the proposed GEM Executable. It is 

likely there will be updates to the GEM Executable for the Final Rule. The constants for the proposed 

GEM-based equation and the standards generated from the equation are subject to change as a result of 

those updates. Note that the equation constants, and the resulting standards, in the attached spreadsheet 

vary slightly from those in the preamble and regulations of the NPRM. See our memo to the docket 

titled:

“Numerical Standards for Tractors, Trailers, and Vocational Vehicles Based on the GEM Executable Code; 

and Derivation of the Numerical Engine Standards” July 2015

The spreadsheet is for illustrative purposes only. It will provide an estimate of the CO2 emissions, but 

these values cannot be used for compliance. EPA and NHTSA will make a formal compliance template 

after we issue the Final Rule. The calculations do not use the same method for rounding results as used 

in compliance. Also, these calculations do not consider deficits that we are currently proposing to allow 

manufacturers to generate and carry-over for up to three years. All regulation references in this memo 

are with respect to the proposed provisions in Title 40 of the Code of Federal Regulations.

Using the Spreadsheet

In the attached spreadsheet, users can update the white-colored cells with their trailer information. The 

green cells will automatically update according to those inputs. The second tab (“ForReference”) 

includes tables from the proposed regulations. None of the information in the ForReference tab is used 

for calculations. These tables may help users identify appropriate values for the inputs. 
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Users can change the model year (white box above the Calculation Table) to the year of interest. The 

standards will update automatically. Note that we are not proposing standards before MY 2018 and no 

standards will be shown if a year earlier than 2018 is used. 

In the Calculation Table, Column A is for the trailer Configuration name. This can be any userspecified name to identify a given set of trailers; it does not factor into the calculations. A single 

“configuration” would include a unique set of work performing devices (Columns D and E), and 

performance characteristics (Columns F-I). Column B identifies the trailer subcategory based on length 

and whether it is a dry or refrigerated van. Column C is the Averaging Set/Family. By default, there are 

four averaging sets that align with the subcategories (i.e., LDV, LRV, SDV, and SRV), but 

manufacturers can include trailers with less-stringent standards in a more-stringent averaging set to 

reduce the number of tests and reporting required. See 1037.230(d) and 1037.740(a). For instance, a 

long refrigerated van (LRV) configuration could be included in the long dry van (LDV) family, because 

LDVs have more-stringent standards.

If a trailer configuration has one or more of the “work performing devices” in Columns D and E, users 

would enter a “Y” in the field. Otherwise they would enter an “N”. These columns are used to 

determine any reduced aero options (i.e., partial- or non-aero) that are available for the given 

configuration. Column K will automatically display the aero options. Any configuration that has a “Y”

in both Columns D and E would be a “Non-Aero” trailer. There are no numerical standards for non-aero 

trailers and no CO2 value is calculated. Configurations that have a “Y” in one of the work-performing 

device columns are eligible for the “Partial-Aero” option in MY 2027 and later. For years earlier than 

2027, Column K will show that these configurations are “Full-Aero”, since the proposed standards are 

the same for full- and partial-aero trailers during those model years. If users do not want to consider 

partial-aero trailers (i.e., believe they can meet the full-aero standard in 2027), they would change any 

“Y” entries in under the Work-Performing Devices columns (Columns D and E) to “N” and those 

trailers would be factored into the full-aero calculations.

Columns F through I are the performance parameters used as inputs to the proposed GEM-based 

compliance equation. If the trailer configuration has an automatic tire inflation system (ATIS) installed, 

users enter a value of 0.985 in Column F. Otherwise, users enter a value of 1.0. Tire rolling resistance 

level (TRRL) values in Column G are the coefficient of rolling resistance (CRR) values, likely obtained 

from testing performed by the tire manufacturers. TRRL values can range from 3.0 to 7.0 kg/ton. Delta 

CDA values in Column G would come from aerodynamic tests performed by the trailer manufacturer, a 

contractor, or an aero device manufacturer that had its results pre-approved. The aero test results would 

determine which of the trailer aerodynamic bins in Table 2 of 1037.515 applies, and the user would 

enter the associated delta CDA from the table into Column H for the given configuration. Weight 

reduction values are obtained from the list of qualifying component substitutions in Table 3 of 1037.515 

(trailer-specific components) and Table 7 of 1037.520 (wheel-related weight reductions). Users would 

sum the weight of all qualifying components installed on the given configuration, and enter that value in 

Column I. The TRRL and Delta CDA values should be rounded to the nearest tenth (0.1). The Weight 

Reduction values should be rounded to the nearest whole number (1.0). The aerodynamic bin table and 

the two weight reduction tables from the proposed regulations are reproduced in the “ForReference” tab 

of the spreadsheet.
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This spreadsheet will not provide a warning if performance parameters are out of range. Table 1 below 

summarizes the limits for each parameter. Note that CO2 will only be calculated if all four performance 

parameter columns contain values. 

Table 1: Limits for Performance Parameters in Proposed GEM-Based Trailer Compliance Equation

User-Defined Performance Parameter Units Minimum

Value

Maximum

Value

Aerodynamic Drag Area (CdA) m^2 0.0 2.0

Tire Rolling Resistance Level (TRRL) kg/t 3.0 7.0

Weight Reduction lbs 0.0 10,000

Automatic Tire Inflation System none 0.985 (yes) 1.0 (no)

The final user input is the production volume in Column J. Users would enter the number of trailers 

sold for that given configuration. This value is used to calculate the average for each full-aero averaging 

set/family. 

Columns K through O of the Calculation Table display the results for each configuration. Non-Aero 

trailers do not have numerical standards and have an “N/A” in the columns that refer to standards. 

Partial-aero trailers have numerical standards, but are not eligible for averaging in this proposal. As a 

result, each partial-aero trailer configuration must meet the standard to comply. In the spreadsheet, rows 

that contain partial-aero configurations that are above the standard are highlighted pink so users can 

easily identify those trailers. Full-aero trailers are not highlighted if they are above the standard, 

because those trailers could be accounted for with averaging. 

The results are summarized in the two tables at the top of the worksheet. Summary Table 1 summarizes 

the results for the full-aero box trailer families that are eligible for averaging in the proposed rule. 

Summary Table 2 summarizes the results for the partial- and non-aero box trailer families that are not 

eligible for averaging in the proposal. 

In Summary Table 1 calculations that do not apply (i.e., a trailer type is not included in the Calculation 

Table) are shown as “N/A”. The first row of Summary Table 1 displays the production-weighted

average for each family, considering the production volume of individual configurations in the family. 

The second row shows the proposed standard for the given family in that model year for comparison,

and the third row indicates if the average value meets the standard (“NO” if above and “yes” if at or 

below the standard). The last three rows are for reference only. They are not used in the calculation. 

They indicate the number of configurations that are above the standard, the total number of 

configurations in that family, and the total production volume of that family. If the “Total 

Configurations Above Standard” row is zero for any family, averaging is not required, since all trailers 

within that family are compliant. 

Summary Table 2 does not contain an average CO2 value, because all configurations that are assigned a 

partial- or non-aero status must meet their reduced-aero standards. For reference, the table shows the 

standard for the family, followed by the number of configurations that are above the standard, the total 

configurations in the family, and the total production volume for the family. As mentioned previously, 
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all partial-aero configurations that are above the standard are highlighted in pink in the Calculation 

Table to quickly identify them.

 

Conclusion

This spreadsheet is intended to provide an estimate of CO2 emissions. This spreadsheet cannot be used 

for compliance and users should not expect that the results from these calculations will match those from 

official compliance calculations. 

Attached:

Example Trailer Emissions Calculations Spreadsheet – [filename]