Greenhouse Gas Emissions Model
(GEM) User Guide
Vehicle Simulation Tool for Compliance
with the Greenhouse Gas Emissions
Standards and Fuel Efficiency Standards
for Medium and Heavy-Duty Engines
and Vehicles: Phase 2

%	United States
Environmental Protect

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Greenhouse Gas Emissions Model
(GEM) User Guide
Vehicle Simulation Tool for Compliance
with the Greenhouse Gas Emissions
Standards and Fuel Efficiency Standards
for Medium and Heavy-Duty Engines
and Vehicles: Phase 2
Assessment and Standards Division
Office of Transportation and Air Quality
U.S. Environmental Protection Agency
United States
Environmental Protection
^1	Agency
EPA-420-B-16-067

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Table of Contents
I.	Introduction	3
II.	Installation	3
II. A. Computer Requirements	3
II.B. Installation Instructions	3
II.C. Contents of Installation Package	8
II.D. Sample Input Files	9
II.E.	GEM Executable	10
III.	Model Description	10
III.	A. GEM Architecture and Summary of Upgrades	10
III.B.	Vehicle Parameters for Each Regulatory Subcategory	12
III.B. 1. Drive Cycles and Cycle Average Engine Fuel Map	12
III.B.2. Tractor Vehicle Parameters	13
III.B.3. Vocational Vehicle Parameters	16
III.B.4.	Trailer Vehicle Parameters	20
IV.	GEM Input File Structure	22
IV.	A.	Note to Users Creating or Editing .csv Files Using Microsoft Excel	22
IV.B.	Tractor Input Files	23
IV.C.	Vocational Input Files	28
IV.D.	Trailer Input Files	33
IV.E.	Supplemental Input Files	35
IV.E.	1. Engine Input File for Tractor and Vocational Vehicles	35
IV.E.2. Transmission Input File for Tractor and Vocational Vehicles	37
IV.E.3. Optional Powertrain Input File for Tractor and Vocational Vehicles	38
IV.E.4. Optional Axle Input File for Tractor and Vocational Vehicles	39
V.	GEM Output File Structure	40
V.	A. Standard GEM Outputs for Compliance	40
V.B.	Optional GEM Outputs for Cycle-Specific Information	41
VI.	Running GEM	42
VI.A.	Preparing for GEM Runs	42
VI.A. 1. Cycle Average Fuel Map for Tractor and Vocational Vehicles	42
VI. A.2. Testing Input Files for Errors	43
VI.B. Running GEM Using the Start Menu and Desktop Icon	45
VI.C. Running GEM Using the Command Prompt	48
VII.	Final Notes	51

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I. Introduction
The Greenhouse gas Emissions Model (GEM) was first created by EPA as part of the
"Heavy-Duty Greenhouse Gas Emissions Standards and Fuel Efficiency Standards for Medium-
and Heavy-Duty Engines and Vehicles: Phase 1" rulemaking finalized in 2011. The model was
developed to serve as a means for determining compliance with EPA's GHG emissions and
NHTSA's fuel consumption Phase 1 vehicle standards for Class 7 and 8 combination tractors and
Class 2b-8 vocational vehicles.
For the Phase 2 rulemaking, significant enhancements were made to the model. In
addition to the model released with the Notice of Proposed Rulemaking (NPRM), additional
refinements were made to the model based on public comments received from our NPRM and
subsequent Notice of Data Availability (NODA) releases.
This User Guide describes the Phase 2 GEM release, GEM P2v3.0, published with the
Phase 2 final rulemaking (FRM). The following sections include installation instructions, a
general model description, and instructions for running the model, including a description of the
necessary input and resulting output files. A detailed description of the model architecture and
updates, including changes from our Phase 1 GEM release (GEM version 2.0.1), NPRM release
(GEM P2v2.0) and NODA release (GEM P2v2.1), can be found in Chapter 4 of the Phase 2 RIA.
II. Installation
II.A. Computer Requirements
EPA developed Phase 2 GEM to be a forward-looking Matlab/Simulink-based model for
heavy-duty (Class 2b-8) vehicle compliance for the Phase 2 rulemaking. The model is a free,
desktop computer application provided as an executable to be operated on a single computer.
Since it is provided as an executable, the user does not have to have access to the
Matlab/Simulink software packages.1 The following minimum computer specifications are
required for the model to run:
-	Operating System: 64-bit Windows 7 or newer
-	CPU: 2 GHz processor
-	Memory: 4 GB of RAM
II.B. Installation Instructions
The downloadable installation file is available on EPA's website (see Figure 1) at:
www 3. epa.gov/otaq/climate/gem. htm.
A link to the most recent GEM version will be located at the top of the page. The GEM
executable is bundled with this User Guide and several input file templates into a file that can be
downloaded in a single step. A copy of this User Guide is also available on the website for
convenience. Note that the GEM executable, sample files and documentation require about 10
1 The Matlab and Simulink models that make up the GEM source code are available in the docket to the Phase 2
rulemaking. Please see Docket: EPA-HQ-OAR-2014-0827 available at: www.regulations.gov.

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MB of free space. Users that also require the Matlab Compiler Runtime application (see Figure
7) will need about 700 MB of free space.
To request a CD of this software instead of downloading it, or to request assistance if you
have trouble with accessibility of this software, please request through an email addressed to
OTAQ@epa.gov.
\#EFYV United Stains Environmental Protection AuwMrtf



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<*Greenhouse Gas Emissions Model (GEM) for Medium- and Heavy-Duty Vehicle Compliance
Greenhouse Gas Emissions Model (GEM) for Medium-
and Heavy-Duty Vehicle Compliance
EPA's Greenhouse Gas Emissions Model (GEM) is a free, desktop computer
application that estimates the greenhouse gas (GHG) emissions and fuel
efficiency performance of specific aspects of heavy-duty vehicles. GEM is
designed to operate on a single computer.
If you have trouble downloading this software, please contact EPA,
NOTE You wH nd Adobe Acrobat
Reader, available ai a free download,
re view seme of the files on this page
See EPA's PDF page to learn more
about PDF, and for a link to the free
No#l Phase 2 GEM Simulation Model (Supporting the Final Heavy-Duty Vehicle Greenhouse
Gas Emissions and Fuel Efficiency Rules)
The model documentation provides details on how to install and use the model. The pdf file also contains the input files
that were used to determine the stringency of the final Greenhouse Gas Emissions Standards and Fuel Efficiency
Standards for Medium- and Heavy-Duty Vehicles, The downloadable installation file below contains the application
executable Files for the active version of Phase 2 GEM for simulating vehicle compliance.
 Greenhouse Gas Emissions Model (GEM) user Manual Vehicle Simulation Tool for Compliance with Greenhouse
Gas Emissions Standards and Fuel Efficiency Standards for Medium and Heavy-Duty Engines and Vehicles
Climate Change Home
Transportation &
Climate Home
Basic Information
What You Can Do
Regulation* A
Standards
Measuring GHGs
Strategies & Analysis
Fur-Is
Vehicle Technologies
Travel Efficiency
Related links
- Download the executable version of GEM_Setup_x64.exe (zip)
 Phase 2 GEM Simulation Model (Supporting the Proposed Phase 2 Fleavy-Duty Vehicle
Greenhouse Gas Emissions and Fuel Efficiency Rules)
The model documentation provides details on how to install and use the model. The pdf file also contains the input files
that were used to determine the stringency of the proposed Greenhouse Gas Emissions Standards and Fuel Efficiency
Standards for Medium- and Heavy-Duty Vehicles. The downloadable installation file below contains the application
Figure 1: EPA Website to Obtain GEM Installation Package
Currently, GEM is only available to computers using 64-bit Windows operating systems
(Windows 7 and newer). To check your computer's operating system, right click on "Computer"
from a desktop icon or the Windows Start Menu and select the System Properties window. If
your computer has a 64-bit operating system, it will be noted on the properties window, as is
seen in Figure 2.

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Figure 5: Start Menu Folder for Phase 2 GEM Download; the Agencies Recommend the Default Folder
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The next screen gives users an option to create a shortcut to Phase 2 GEM on their
desktop. Users that choose to install a desktop icon will see a "Phase 2 GEM" shortcut, similar
to the one shown in Figure 6, on their desktop. Users can uncheck the box next to the "Create a
desktop icon" if they do not wish to have a desktop shortcut.

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Phase2 GEM
Figure 6: Desktop Icon Shortcut to Phase 2 GEM
Phase 2 GEM requires the use of Matlab Runtime Compiler and Microsoft Visual C++
2005 or 2008 Redistributable (x64). The setup wizard will install Matlab Runtime Compiler
R2014a (version 8.3) if the box, shown in Figure 7, is checked. For computers that already have
the runtime compiler (R2014a) installed, users can uncheck this box to avoid reinstallation.
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Figure 7: Additional Installation Options for Phase 2 GEM; Matlab Runtime Compiler R2014a is Required
for GEM
The following windows allow users to review the installation settings and install Phase 2
GEM. The installer will warn users if their computers do not have Microsoft Visual C++ 2005
or 2008 Redistributable (x64) installed. A pop-up window will initiate installation of this
software and will remain displayed until installation is complete.
A final screen (Figure 8) will show up when Phase 2 GEM has completed installing. The
installation process for Matlab Runtime Compiler (if selected) will initiate shortly after this
completion screen appears. The Matlab setup wizard for the runtime compiler is not described in
this User Guide.

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$ Setup - Phase 2 GEM
Completing the Phase 2 GEM
Setup Wizard
Setup has finished installing Phase 2 GEM on your computer.
The application may be launched by selecting the installed
icons.
Click Finish to exit Setup.
Figure 8: Installation Complete Window for Phase 2 GEM
II.C. Contents of Installation Package
Once installed, several files are stored in the installation location selected (i.e.,
C. 'Program Files'US EPA Phase 2 GEM\ by default). Fi gure 9 shows the contents of the default
installation folder. Users can access the GEM User Guide (Documentation folder), the GEM
executables, and sample files (Sample Input Files folder) from this directory. They can also
uninstall GEM and remove all of its contents by clicking on the "unins000.exe" executable

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Figure 9: Contents of Installation Folder for Phase 2 GEM
GEM is also available from the Start Menu, under the folder named "EPA Phase 2
GEM", as seen in Figure 10. Within the Start Menu folder, users have access to the executables
(described in the Running GEM section of this Guide), as well as a copy of this User Guide, a
link to the EPA website, additional documentation, and sample input files that can be used as
templates for running GEM.

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II.D. Sample Input Files
Sample input files are stored with the Phase 2 GEM executable. As seen in Figure 11,
the "Sample Input Files - RELOCATE BEFORE USE" folder includes sample vehicle input
files for each of the three vehicle regulatory subcategories, four folders with example engine,
transmission, axle and powertrain input files, and two files to generate cycle averaged fuel maps.
A description of each of these input files and instructions for running the model are provided in
later sections.

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Figure 11: Sample Input Files Included with EPA Phase 2 GEM

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If users select the default installation folder, C:\Program Files\US EPAVPhase 2 GEM\, it
is recommended that they copy the folder "Sample Input Files - RELOCATE BEFORE USE"
from this default folder to a local folder. By doing so, users can easily run GEM and write output
results into the selected local folder and avoid potential administrative rights issues, since not all
organizations allow users to write files to C:\Program Files folders. Users can copy the sample
files folder to any convenient local folder and can rename it as needed once it is copied to its new
destination.
II.E.	GEM Executable
The Phase 2 GEM executable does not require the use of Matlab or Simulink software,
and the agencies require tractor and vocational vehicle manufacturers to use the executable for
demonstrating compliance with the CO2 and fuel consumption standards.2 Phase 2 GEM does
not offer a graphical user interface (GUI) for users to provide their vehicle parameters. Instead,
inputs are provided in a comma delimited (.csv) file. Results are available in a generated report
that can be viewed using either a text editor or spreadsheet. The following sections will describe
the model, its input files, and its output files in more detail.
III. Model Description
Phase 1 GEM was updated in order to meet Phase 2 rulemaking requirements. Phase 2
GEM improves the fidelity of the Phase 1 model to better match the function of the simulated
vehicles and accurately reflect changes in technology for compliance purposes. Many of the
modifications were the result of numerous constructive comments from both public comments
and GEM peer reviews3. The following sections describe the model with an emphasis on the
additional vehicle parameters available in the Phase 2 upgrade of the model. Users are directed
to Chapter 4 of the RIA for more detailed information regarding the model architecture and
validation.
III.A.	GEM Architecture and Summary of Upgrades
The GEM architecture is comprised of four systems: Ambient, Driver, Powertrain, and
Vehicle as seen in Figure 12. The Powertrain and Vehicle systems consist of one or more
subcomponent models and a description of the subcomponent models is available in Chapter 4 of
the Phase 2 RIA.
2 Trailer manufacturers will use a GEM-based equation and are not required to use GEM. For convenience, this
User Guide provides instructions for using GEM for trailers, but manufacturers cannot use GEM for demonstrating
compliance.
3"Peer Review of the Greenhouse gas Emissions Model (GEM) and EPA's Response to Comments," Docket # EPA-
420-R-15-009, June 2015.

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The agencies are adopting additional regulatory subcategories to better represent the
heavy-duty vehicles and these subcategories are reflected in the model with additional vehicle
models. Phase 2 GEM also incorporates improvements to the duty cycles, including the addition
of idle cycles for vocational vehicles, and modified cruise cycles that account for changes in road
grade. Specifically, the agencies implemented the following key technical features into Phase 2
GEM:
An upgraded engine controller, which includes engine fuel cut-off during braking and
deceleration, and a cycle average method to supplement the steady state fuel map for
transient simulation, and optionally apply to the cruise cycles
An upgraded transmission model, which includes newly developed automatic and
automated manual transmissions. An optional transmission power loss input is also
available.
An option to input axle power losses as a function of axle output speed and torque
An upgraded driver model with a distance-compensated driver that will drive the
certification drive trace over a prescribed distance regardless of increased drive time due
to vehicle under-performance, for example

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With these upgrades, the model is capable of recognizing most technologies that could be
evaluated in both engine and chassis dynamometers and is better able to reflect changes in
technologies for compliance purposes. See Chapter 4 of the RIA for more information about
these upgrades.
III.B. Vehicle Parameters for Each Regulatory Subcategory
GEM is a flexible simulation platform that can model a wide variety of Class 2b to Class
8 vehicles. The key to this flexibility is the component description files that can be modified or
adjusted to accommodate vehicle-specific information. Phase 2 GEM includes four main vehicle
types, and several variations of each vehicle, to match the regulatory subcategories in the Phase 2
rulemaking. Each regulatory subcategory is associated with specific vehicle parameters and
technology options.
The agencies predefined many key parameters, since those parameters are either hard to
quantify due to lack of certified testing procedures or difficult to obtain due to proprietary
barriers. Examples of these parameters include transmission shifting strategies and engine
inertia. The values selected for these parameters are a result of substantial testing by EPA, as
well as confidential discussions with engine, chassis and component manufacturers. Some
default parameters have optional overrides, requiring additional testing.
Each vehicle subcategory has a set of user-defined parameters. These parameters
include vehicle technologies or component attributes that impact CO2 emissions and fuel
consumption, but have the potential to vary across manufacturers. Depending on the regulatory
subcategory, parameters such as aerodynamic performance, tire rolling resistance, vehicle
weight, engine fuel map, transmission gear ratios, tire radius, or axle ratio can be changed as
inputs by the user.
The sections to follow outline the regulatory vehicle subcategories that manufacturers
may select in GEM for compliance, and summarize the user-defined and predefined model
parameters applicable to each subcategory.
III.B.l.Drive Cycles and Cycle Average Engine Fuel Map
The Phase 2 rulemaking also predefines three drive cycles including a transient cycle and
two cruise speed cycles. The transient mode is defined by California Air Resources Board
(CARB) in their Highway Heavy-Duty Diesel Transient (HHDDT) cycle. The cruise speed
cycles are represented by two nominally constant speed 65 mph and 55 mph cycles, each with
varying road grade. For vocational vehicles two additional idle cycles are utilized, one
simulating parked idling operation and the other idling in traffic. Each regulatory subcategory is
assigned a specific set of drive cycle weightings.
The agencies recognize the limitation of the steady state engine fuel map for transient
simulation, and we are requiring that a cycle average fuel map be generated to supplement the
steady state fuel map for the transient cycle. Additionally, users have the option to apply the
cycle average method to the 55 and 65 mph cruise cycles as well. A summary of the procedure
to generate the cycle average map(s) is provided in the Supplemental Input Files section of this
Guide. A detailed description and justification for the cycle average method can be found in
Chapter 4 of the RIA.

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III.B.2.Tractor Vehicle Parameters
The agencies are adopting a set of predefined modeling parameters to establish consistent
combination tractor models from which tractor manufacturers can compare their vehicle
improvements. GEM recognizes twelve variations of combination tractors. Class 8 tractors can
have day or sleeper cab configurations with low, mid, or high roof heights. Class 7 tractors are
only available in a day cab configuration, but also have low, mid, or high roof options. GEM
also recognizes Class 8 heavy-haul tractors with a single vehicle for all cabs and roof heights,
and six optional heavy Class 8 tractor subcategories to represent tractors with higher gross
combined weight rating (GCWR) that are designed for heavy-haul operation in Canada. Within
GEM, high roof tractors are simulated as pulling a standard box van. Mid roof tractors and low
roof tractors are simulated as pulling tank and flatbed trailers, respectively. The standard box
van for high roof tractor simulations also includes a skirt, which impacts the user-defined
aerodynamic drag area input, CdA (described in the next section).
Table 1 through Table 6 summarize the predefined modeling parameters for default
tractor subcategories. The standard Class 8 payload is 19 tons. All Class 8 heavy-haul tractors,
including the optional heavy Class 8, have a payload of 43 tons. The Class 7 payload is 12.5
tons. Sleeper cab tractors are assigned drive cycle weightings that are more representative of
long-haul driving with 86 percent at 65mph, 9 percent at 55 mph and 5 percent transient. Drive
cycle weightings for day cab tractors are more representative of short-haul driving with 64
percent at 65 mph, 17 percent at 55 mph, 19 percent transient.
Table 1: Class 8 Combination Tractor Sleeper Cab Predefined Modeling Parameters
Regulatory Subcategory
Class 8 Combination, Sleeper Cab
Roof Height
High Roof
Mid Roof
Low Roof
Total Weight (kg)
31978
30277
30390
Number of Axles
5
Payload (tons)
19
CARB HHDDT Drive Cycle Weighting
0.05
GEM 55 mph Drive Cycle Weighting
0.09
GEM 65 mph Drive Cycle Weighting
0.86
Table 2: Class 8 Combination Tractor Day Cab Predefined Modeling Parameters
Regulatory Subcategory
Class 8 Combination, Day Cab
Roof Height
High Roof
Mid Roof
Low Roof
Total Weight (kg)
31297
29529
29710
Number of Axles
5
Payload (tons)
19
CARB HHDDT Drive Cycle Weighting
0.19
GEM 55 mph Drive Cycle Weighting
0.17
GEM 65 mph Drive Cycle Weighting
0.64

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Table 3: Class 8 Heavy-Haul Combination Tractor (All Cabs) Predefined Modeling Parameters
Regulatory Subcategory
Class 8 Combination, Day Cab
Roof Height
All Roof Heights
Total Weight (kg)
53750
Number of Axles
5
Payload (tons)
43
CARB HHDDT Drive Cycle Weighting
0.19
GEM 55 mph Drive Cycle Weighting
0.17
GEM 65 mph Drive Cycle Weighting
0.64
Table 4: Class 7 Combination Tractor Predefined Modeling Parameters
Regulatory Subcategory
Class 7 Combination, Day Cab
Roof Height
High Roof
Mid Roof
Low Roof
Total Weight (kg)
22679
20910
21091
Number of Axles
4
Payload (tons)
12.5
CARB HHDDT Drive Cycle Weighting
0.19
GEM 55 mph Drive Cycle Weighting
0.17
GEM 65 mph Drive Cycle Weighting
0.64
Table 5: Heavy Class 8 Combination Tractor Sleeper Cab Predefined Modeling Parameters
Regulatory Subcategory
Class 8 Combination, Sleeper Cab
Roof Height
High Roof
Mid Roof
Low Roof
Total Weight (kg)
53750
52049
52162
Number of Axles
5
Payload (tons)
43
CARB HHDDT Drive Cycle Weighting
0.05
GEM 55 mph Drive Cycle Weighting
0.09
GEM 65 mph Drive Cycle Weighting
0.86
Table 6: Heavy Class 8 Combination Tractor Day Cab Predefined Modeling Parameters
Regulatory Subcategory
Class 8 Combination, Day Cab
Roof Height
High Roof
Mid Roof
Low Roof
Total Weight (kg)
53069
51301
51482
Number of Axles
5
Payload (tons)
43
CARB HHDDT Drive Cycle Weighting
0.19
GEM 55 mph Drive Cycle Weighting
0.17
GEM 65 mph Drive Cycle Weighting
0.64
Table 7 shows the predefined modeling parameters that are consistent across all tractor
types. These common parameters include ambient temperature, efficiencies and accessory
powers. The calculations for overall rolling resistance and the distribution of weight savings are
also consistent for all simulated tractors.

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Table 7: Common Predefined Modeling Parameters for All Simulated Combination Tractors
AMT Gearbox Mechanical Efficiency
(9 or more gears)
96% for low gears, 98% high gears, except 100% for 1:1 gear ratio
AMT Gearbox Mechanical Efficiency
(fewer than 9 gears)
100% for 1:1 gear ratio, 98% for rest of gears
AT Gearbox Mechanical Efficiency
95.5% for 1:1 gear ratio, 98% for rest of gears
Electrical Accessory Power (W)
1200
Mechanical Accessory Power (W)
2300
Environmental air temperature (C)
25
Weight Reduction (lbs)
Add 1/3 *weight reduction to Payload tons, 2/3 *weight reduction is
subtracted from the vehicle mass during simulation
Trailer Tire Crr (kg/t)
6.0
Overall Tire Crr (kg/t)
= 0.425*Trailer Crr + 0.425*Drive Crr + 0.15*Steer Crr
The "low gears" mentioned in the AMT gearbox efficiency of Table 7 only applies when
the total gear number of a transmission is greater than 9. In this type of transmission, low gear
efficiency will be set to 96% when the lower gears is equal to a maximum value of either total
gear number divided by 2 or the total gear number minus 6. Taking a transmission with 10 gears
for example, the lower gear is defined as maximum of 10/2 or 10-6, which will be 5. This means
that any gear numbers smaller than 5 will have 96% efficiency. For AMTs with less than 9
gears, such as 8 or less, all gears efficiency will be set to 98% except the 1:1 gear ratio.
GEM allows a user to modify or adjust performance information for certain components
in order to model and quantify improvements the manufacturer is making to its vehicles. Table 8
lists the user-defined modeling parameters that are recognized in GEM. In addition to tire rolling
resistances, Phase 2 GEM also requires axle configuration, axle ratio, and loaded size of the tires.
Similar to Phase 1, Phase 2 GEM also accounts for aerodynamic drag, but manufacturers are
asked to provide a wind-averaged aerodynamic drag area (CdA). Note that in MY 2027 and
later, GEM will subtract 0.3 m2 from the user's CdA input value for high roof tractors to account
for improved box trailer aerodynamics. See Section III.E.2 of the preamble to this rulemaking
for more information.
In Phase 1, a default engine and transmission were applied to all GEM-simulated
combination tractors. For most simulated vehicles, Phase 2 GEM requires manufacturers to
supply an engine fuel map and specific transmission information as separate input files to the
model. Manufacturers also have the option to use engine and transmission performance data
obtained from a powertrain test in their GEM runs and replace the engine and transmission files
with a single powertrain file. Additionally, manufacturers can optionally include a file to
account for axle losses and/or include a file to account for transmission power losses. These
input files have specific requirements, as will be discussed in the Supplemental Input Files
section of this Guide.

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Table 8: User-Defined Modeling Parameters for Class 7 and Class 8 Combination Tractors (All Cabs and
Roof Heights)
Modeling Parameter
Method of Determining Parameter
Engine data file
40 CFR 1036.510, 1036.535 and 1036.540
Transmission data file
40 CFR 1037.520(g)(1) and optionally 1037.565
Powertrain data file (Optional)
40 CFR 1037.550
Drive Axle Configuration
40 CFR 1037.520(g)(2)
Drive Axle Ratio
40 CFR 1037.520(g)(3)
Drive Axle data file (Optional)
40 CFR 1037.560
Aerodynamic Drag Area, CdA (m2)
See 40 CFR 1037.520(b)
Steer Axle Tire Rolling Resistance (kg/t)
40 CFR 1037.520(c)
Drive Axle 1 Tire Rolling Resistance (kg/t)
Drive Axle 2 Tire Rolling Resistance (kg/t)
Drive Axle Loaded Tire Size (rev/mi)
See 40 CFR 1037.520(c)
Phase 2 GEM also accounts for additional technology improvements that reduce CO2 and
fuel consumption, but are not easily captured in the vehicle simulation. These reduction values
vary for each technology. The vehicle speed limiter, weight reduction and neutral idle options
will impact the vehicle simulation. The remaining technologies improvements are applied as
post-process percent reductions to the results from the vehicle simulation. Table 9 directs users
to the corresponding regulation reference to determine appropriate values to apply for each
technology.
Table 9: Technology Improvement Options for Tractor Manufacturers
Technology Improvement
Regulation Reference
Vehicle Speed Limiter (MPH or NA)
40 CFR 1037.520(d)
Weight Reduction (lb)
40 CFR 1037.520(e)
Neutral Idle, AT only (Y/N)
40 CFR 1037.660
Intelligent Controls (%)
40 CFR 1037.520(j)
Accessory Load (%)
40 CFR 1037.520(j)
Extended Idle Reduction, Sleeper Cabs Only (%)
40 CFR 1037.520(j)
Tire Pressure System (%)
40 CFR 1037.520(j)
Other (%)
40 CFR 1037.520(j)
III.B.3 .Vocational Vehicle Parameters
The agencies are adopting a set of predefined modeling parameters to establish consistent
vocational vehicle models from which manufacturers can compare their vehicle improvements.
GEM recognizes nine variations of vocational vehicles based on both vehicle weight class and
duty cycle. Class 8 vocational vehicles are considered heavy heavy-duty (HHD). Classes 6 and
7 are medium heavy-duty (MHD), and Classes 2b-5 are considered light heavy-duty (LHD). As
seen in Table 10, Table 11, and Table 12, the weight, number of axles, aerodynamic drag area
and payload are the same for all of the vehicles within a weight class. Vehicles within each

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weight class are further categorized using three duty cycles (Regional, Multi-purpose and Urban)
by varying the drive cycle weightings associated with each composite duty cycle.
The regulations describe the drive cycle weighting factors for each subcategory in 40
CFR 1037.510. Manufacturers should consult the regulations at 40 CFR 1037.510(c) as well as
40 CFR 1037.140(g-h) and 40 CFR 1037.150(z) for instructions on how to select the appropriate
subcategory in which to certify a vocational vehicle configuration. The reasoning behind the
regulations can be found in the preamble to the rule in Section V.D.l.e.
Table 10: Vocational Heavy Heavy-Duty (Class 8) Vehicle Predefined Modeling Parameters
Regulatory Subcategory
HHP
Duty Cycle
Regional
Multi-Purpose
Urban
Total weight (kg)
19051
CdA (m2)
6.86
Payload (tons)
7.50
ARB Transient Drive Cycle Weighting
0.20
0.54
0.90
GEM 55 mph Drive Cycle Weighting
0.24
0.23
0.10
GEM 65 mph Drive Cycle Weighting
0.56
0.23
0.00
Parked Idle Cycle Weighting
0.25
0.25
0.25
Drive Idle Cycle Weighting
0.00
0.17
0.15
Non-Idle Cycle Weighting
0.75
0.58
0.60
Table 11: Vocational Medium Heavy-Duty (Class 6-7) Vehicle Predefined Modeling Parameters
Regulatory Subcategory
MHD
Duty Cycle
Regional
Multi-Purpose
Urban
Total weight (kg)
11408
CdA (m2)
5.40
Payload (tons)
5.60
ARB Transient Drive Cycle Weighting
0.20
0.54
0.92
GEM 55 mph Drive Cycle Weighting
0.24
0.29
0.08
GEM 65 mph Drive Cycle Weighting
0.56
0.17
0.00
Parked Idle Cycle Weighting
0.25
0.25
0.25
Drive Idle Cycle Weighting
0.00
0.17
0.15
Non-Idle Cycle Weighting
0.75
0.58
0.60
Table 12: Vocational Light Heavy-Duty (Class 2b-5) Vehicle Predefined Modeling Parameters
Regulatory Subcategory
LHD
Duty Cycle
Regional
Multi-Purpose
Urban
Total weight (kg)
7257
CdA (m2)
3.40
Payload (tons)
2.85
ARB Transient Drive Cycle Weighting
0.20
0.54
0.92
GEM 55 mph Drive Cycle Weighting
0.24
0.29
0.08
GEM 65 mph Drive Cycle Weighting
0.56
0.17
0.00
Parked Idle Cycle Weighting
0.25
0.25
0.25
Drive Idle Cycle Weighting
0.00
0.17
0.15
Non-Idle Cycle Weighting
0.75
0.58
0.60

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The agencies are also adopting seven custom chassis subcategories for manufacturers that
know the specific end-use of their vehicles. These custom chassis are based on the nine general
vocational subcategories, as shown in Table 13. In contrast to the vocational subcategories in the
main program, custom chassis have several default GEM inputs as will be described in the Input
File Structure section of this Guide.
Table 13: Vocational Custom Chassis Subcategories and Associated Vehicle in GEM
Custom Chassis Subcategory
GEM Simulated Vehicle
Emergency Vehicles
HHD Urban
Cement Mixers and Other Mixed Use Applications
HHD Urban
Refuse Vehicles
HHD Urban
Coach Buses
HHD Regional
Transit Bus, Other Bus and Drayage Tractors
HHD Urban
Motor Homes
MHD Regional
School Bus
MHD Urban
Table 14 shows the predefined modeling parameters that are consistent across all
vocational vehicle types. These common parameters include ambient temperature, efficiencies
and accessory powers. Gearbox mechanical efficiencies for AMT and AT are consistent with the
tractor model (see section III.B.2 of this Guide). The calculations for overall rolling resistance
and the distribution of weight savings are also consistent for all modeled vocational vehicles.
Table 14: Common Predefined Modeling Parameters for All Vocational Vehicles
AMT Gearbox Mechanical Efficiency
(9 or more gears)
96% for low gears, 98% high gears, except 100% for
1:1 gear ratio
AMT Gearbox Mechanical Efficiency
(less than 9 gears)
100% for 1:1 gear ratio, 98% for rest of gears
AT Gearbox Mechanical Efficiency
99.5% for 1:1 gear and 98% for all gears
Electrical Accessory Power (W)
1200 for HHD, 900 for MHD, 500 for LHD
Mechanical Accessory Power (W)
2300 for HHD, 1600 for MHD, 1000 for LHD
Environmental Air Temperature (C degree)
25
Weight Reduction (lbs)
Add 0.5*weight reduction to Payload tons,
0.5*weight reduction is subtracted from the vehicle
mass during simulation
Overall Tire Crr (kg/t)
= 0.7*Drive Crr + 0.3*Steer Crr
GEM allows a user to modify or adjust performance information for certain components
in order to model and quantify improvements the manufacturer is making to its vehicles. Table
15 lists the user-defined modeling parameters that are recognized in GEM for vocational
vehicles. In Phase 1 GEM, vocational vehicle manufacturers were only given the option of
changing the rolling resistance of their steer and drive tires. Phase 2 GEM continues to allow
vocational vehicle manufacturers to model their vehicle's tire rolling resistances, but also
requires axle configuration, axle ratio, and loaded size of the tires for standard vocational chassis
subcategories. The model also provides these subcategories the option to account for
aerodynamic drag as a wind-averaged change in aerodynamic drag area (delta CdA).

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Additionally, Phase 2 GEM requires manufacturers to supply an engine fuel map and specific
transmission information to for each distinct engine and transmission in the vehicles being
modeled. Manufacturers also have the option to use engine and transmission performance data
obtained from a powertrain test in their GEM runs and replace the engine and transmission files
with a single powertrain file. Additionally, manufacturers can optionally include a file to
account for axle losses and/or include a file to account for transmission power losses. Note that
custom chassis manufacturers are only required to provide some of these parameters (i.e., drive
axle configuration and tire rolling resistances) and the rest will be default values.
Table 15: User-Defined Modeling Parameters for Vocational Vehicles (All Weight Classes)
Modeling Parameter
Method of Determining Parameter
Engine data file
40 CFR 1036.535 and 1036.540
Transmission data file
40 CFR 1037.520(g)(1) and optionally 1037.565
Powertrain data file (Optional)
40 CFR 1037.550
Drive Axle Configuration
40 CFR 1037.520(g)(2)
Drive Axle Ratio
40 CFR 1037.520(g)(3)
Drive Axle data file (Optional)
40 CFR 1037.560
Aerodynamic Drag Area, Delta CdA (m2)
40 CFR 1037.520(m) and 40 CFR 1037.527
Steer Axle Tire Rolling Resistance (kg/t)
40 CFR 1037.520(c)
Drive Axle 1 Tire Rolling Resistance (kg/t)
Drive Axle 2 Tire Rolling Resistance (kg/t)
Drive Axle Loaded Tire Size (rev/mi)
See 40 CFR 1037.520(c)
Similar to the tractor model, Phase 2 GEM accounts for additional vocational vehicle
technologies that reduce CO2 and fuel consumption, but are not easily captured in the vehicle
simulation. These reduction values vary for each technology. The vehicle speed limiter, weight
reduction, neutral idle, and start-stop options will impact the vehicle simulation. The remaining
technologies improvements are applied as post-process g/ton-mile or percent reductions to the
results from the vehicle simulation. Table 16 directs users to the corresponding regulation
reference to determine appropriate values to apply for each technology. These technology
improvements are available to all vocational subcategories.
Table 16: Technology Improvement Options for Vocational Vehicle Manufacturers
Technology Improvement
Regulation Reference
Vehicle Speed Limiter (MPH or NA)
40 CFR 1037.520(d)
Delta Power Take Off Fuel (g/ton-mile)
40 CFR 1037.520(k) and 1037.540
Weight Reduction (lb)
40 CFR 1037.520(e)
Neutral Idle (Y/N)
40 CFR 1037.520(h)
Start-Stop (Y/N)
40 CFR 1037.520(h)
Automatic Engine Shutdown
40 CFR 1037.520(h)
Accessory Load (%)
40 CFR 1037.520(j)
Tire Pressure System (%)
40 CFR 1037.520(j)
Other (%)
40 CFR 1037.520(j)

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III.B.4.Trailer Vehicle Parameters
The agencies are adopting an equation-based compliance approach for box trailer
manufacturers and they are not required to certify their trailers using GEM (see 40 CFR
1037.515). However, the equations for each box trailer subcategory are based on the simulated
trailers described in this section. Note that non-box trailers do not use GEM or the GEM-based
equation for compliance and a discussion of non-box trailers is not included in this User Guide.
The following description of the trailer model as it applies to box trailers is included for
informational purposes only.
The agencies are adopting a set of predefined modeling parameters to establish consistent
tractor-trailer models from which box van trailer manufacturers can compare their vehicle
improvements. GEM recognizes four variations of box van based on length. Long box vans
(trailers that are longer than 50-feet) are represented by either a 53-foot dry van or a 53-foot
refrigerated van pulled by a Class 8 high roof sleeper cab tractor in GEM and are given the same
long-haul drive cycle weightings as the Class 8 high roof sleeper cab tractors mentioned
previously. GEM models all short box vans (box trailers 50-feet in length and shorter) as a
single-axle, solo 28-foot dry van or refrigerated van pulled by a Class 7 high roof day cab tractor
with a 4x2 drive axle configuration.
Table 17 and Table 18 summarize the predefined modeling parameters for long and short
box vans, respectively. All long box vans are modeled with tandem axles and a payload of 19
tons and drive cycle weightings that are more representative of long-haul driving (i.e., 86 percent
at 65-MPH, 9 percent at 55-MPH and 5 percent transient). All short box vans are modeled with
a single axle, a payload of 10 tons, and drive cycle weightings more representative of short-haul
driving with 64 percent at 65-MPH, 17 percent at 55-MPH, 19 percent transient. The vehicle
weight varies between dry vans and refrigerated vans to account for the weight of the
refrigeration unit, and weight also varies proportional to the length of the trailer. The baseline
CdA values were obtained from EPA's aerodynamic testing.
Table 17: Predefined Modeling Parameters for Long Box Trailers
Regulatory Subcategory
Long Box
Dry Van
Long Box
Refrigerated Van
Tractor Type
C8 Sleeper Cab - High Roof
Total weight (kg)
31978
33778
Baseline CdA Values (m2)
6.0
6.0
Tractor Engine
15L 455 HP
Tractor Drive Axle Configuration
6x4
Number of Axles
5
Payload (tons)
19
CARB HHDDT Drive Cycle Weighting
0.05
GEM 55 mph Drive Cycle Weighting
0.09
GEM 65 mph Drive Cycle Weighting
0.86

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Table 18: Predefined Modeling Parameters for Short Box Trailers
Regulatory Subcategory
Short Box
Dry Van
Short Box
Refrigerated Van
Tractor Type
C7 Day Cab - High Roof
Total weight (kg)
18306
20106
Baseline CdA Values (m2)
5.6
5.6
Tractor Engine
11L 350HP
Tractor Drive Axle Configuration
4x2
Number of Axles
3
Payload (tons)
10
ARB Transient Drive Cycle Weighting
0.19
GEM 55 mph Drive Cycle Weighting
0.17
GEM 65 mph Drive Cycle Weighting
0.64
Table 19 shows the predefined modeling parameters that are consistent across all trailer
types. Many of these common parameters are associated with the simulated tractor in the tractor-
trailer model. The calculations for overall rolling resistance and the distribution of weight
savings are consistent with the calculations for GEM-simulated tractors.
Table 19: Common Predefined Modeling Parameters for All Box Trailers
Gearbox Efficiency
100% for 1:1 gear ratio, 96% for lower gears or 98% for
rest of gears
Axle Drive Ratio
3.7
Electrical Accessory Power (W)
300
Mechanical Accessory Power (W)
1000
Loaded Tire Size (rev/mi)
512
Steer Tire Crr (kg/t)
6.54
Drive Tire Crr (kg/t)
6.92
Overall Tire Crr (kg/t)
= 0.425*Trailer Crr + 0.425*Drive Crr + 0.15*Steer Crr
Weight Reduction (lbs)
Add l/3*weight reduction to Payload tons
GEM allows a user to modify or adjust performance information for certain components
in order to model and quantify improvements the manufacturer is making to its vehicles. The
trailer program has three user-defined parameters and one pre-defined technology improvement
option that has a specified reduction value associated with its use (see Table 20). Trailer
manufacturers are able to change their tire rolling resistance, aerodynamic drag and cumulative
weight reduction. GEM applies an additional percent improvement value to trailers that have tire
pressure systems installed on their simulated trailer. Separate percentage values apply for tire
pressure monitoring systems (TPMS) and automatic tire inflation systems (ATIS).

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Table 20: User-Defined Modeling Parameters and Technology Improvement Options for Trailers (All
Lengths)
Modeling Parameter
Method of Determining Parameter
Trailer Tire Crr (kg/t)
40 CFR 1037.515(b)
Change in Aerodynamic Drag Area, ACdA (m2)
40 CFR 1037.515(c) and 40 CFR 1037.526
Weight Reduction (lb)
40 CFR 1037.515(d)
Tire Pressure System11
1.2% for ATIS, 1.0% for TPMS, 0 if no system
a Note that 40 CFR 1037.515(a) specifies the tire pressure system values in decimal format, because trailers use
a GEM-based equation for compliance. The GEM input file described in this Guide uses percent-based input
values for tire pressure systems.
IV. GEM Input File Structure
As mentioned previously, Phase 2 GEM does not offer a graphical user interface (GUI)
for users to provide their vehicle parameters. Instead, inputs are exclusively provided to the
model in a .csv file. Phase 2 GEM executable can be initiated using the Start Menu, or a
command prompt. The following subsections describe the input file structures, which are
consistent for each method of running the model.
Some manufacturers may create a script to automatically generate their input files in .csv
format. Others may wish to manually populate their files using a spreadsheet tool, such as
Microsoft Excel, to easily view the input fields in a column format, and save the files in a .csv
format. For illustration purposes, the .csv input files in this section are shown in spreadsheet
format. The following section, Running GEM, describes the options for running the model.
IV.A. Note to Users Creating or Editing .csv Files Using Microsoft Excel
Users may use Microsoft Excel or any other text editor, such as Notepad, to create or edit
their input files. Once a file is created, it can be saved by going to go to "Save As..and choose
CSV (Comma delimited) (*.csv) in the "Save as type:" pull-down menu, as shown in Figure 13.
In future saves, or when editing and resaving an existing .csv formatted file, users may receive a
warning similar to Figure 14. Select "Yes" to ensure the file is properly saved in .csv format.

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Name
Date modified
Type
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EPA_Sample_Engine_350hp
4/9/201511:50 AM
Microsoft Excel Comma Separated Values F...
36 KB
W Favorites

EPA_Sample_Engine_455hp
4/9/2015 11:50 AM
Microsoft Excel Comma Separated Value F...
36 KB
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Qa] EPA_Sample_Trans_AMT
4/8/201512:53 PM
Microsoft Excel Comma Separated Values F..,
1KB
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5/13/201511:38 AM
Microsoft Excel Comma Separated Values F...
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Gil GEM_Sample_TRACTOR
5/19/2015 9:14 AM
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5/19/20159:10 AM
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Filename: NewFileName
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Authors:
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- Hide Folders XML Data
Single File Web Page
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Figure 13: Example "Save As..." Window to Create a Comma Separated Value (.csv) Input File
Microsoft Excel
Some features in your workbook might be lost if you save it as CSV {Comma delimited),
Do you want to keep using that format?
res
No
Help
Figure 14: Warning from Microsoft Excel When Saving .csv Files Using Excel - Select "Yes"
IV.B. Tractor Input Files
The top of the tractor input file has three comma separated lines that list the regulatory
category, manufacturer name and model year (see Figure 15). Users complete the second
column for each line. The first line must read "Tractor" in order for GEM to run the appropriate
vehicle model. Manufacturer name can be in any format, but it should be consistent with other
regulatory documents from the manufacturer. Model year must be expressed as a four-digit
number.
Regulatory Category Tractor
Manufacturer Name EPA
Model Year	2018
Figure 15: Tractor Input File Header Information
The next lines of the tractor input file contain the model inputs. In the first two columns,
shown in Figure 16, the user provides a Run ED and the Regulatory Subcategory for each run

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The Run ID is a unique value that will be used to identify the ran (e.g., vehicle VIN). It can be
any combination of letters, numbers and separators such as dash periods or
underscores	The Regulatory Subcategory determines the vehicle that is modeled and the
standard that is applied for compliance. For tractors, there are 10 standard regulatory
subcategories in GEM and Table 21 shows the naming convention. In addition, GEM includes
six optional heavy Class 8 tractor subcategories that represent tractors that are designed for
heavy-haul operation in Canada. Manufacturers may optionally certify their tractors as heavy
Class 8, using the subcategories shown in Table 22, starting in MYs 2021. See Section III.B.4.a
of the preamble to this rulemaking for a discussion of these optional tractor subcategories. Note
that these tractors are separate from the C8 HH subcategory that is used for U.S.-based heavy-
haul tractors.
Run ID	Regulatory Subcategory
Unique Identifier (e.g. C8_SC_HR)
Sample_l	C8_SC_HR
Sample_2	C7_DC_MR
Sample_3	C8_HH
Sample_4	HC8_SC_LR
Sample_5	HC8_DC_MR
Sample_6	C8_DC_MR
Sample_7	C8_SC_LR
Sample_8	C8_SC_HR
PT_Samplel	C8_SC_HR
Figure 16: Tractor Input File Run ID and Regulatory Subcategory Inputs
Table 21: Tractor Input File Naming Convention for Tractor Regulatory Subcategories
GEM Input Name
Regulatory Subcategory Description
C8 SC HR
Class 8 Combination, Sleeper Cab - High Roof
C8 SC MR
Class 8 Combination, Sleeper Cab - Mid Roof
C8 SC LR
Class 8 Combination, Sleeper Cab - Low Roof
C8 DC HR
Class 8 Combination, Day Cab - High Roof
C8 DC MR
Class 8 Combination, Day Cab - Mid Roof
C8 DC LR
Class 8 Combination, Day Cab - Low Roof
C8 HH
Class 8 Combination, Sleeper Cab - Heavy Haul
C7 DC HR
Class 7 Combination, Day Cab - High Roof
C7 DC MR
Class 7 Combination, Day Cab - Mid Roof
C7 DC LR
Class 7 Combination, Day Cab - Low Roof
Table 22: Tractor Input File Naming Convention for Optional Heavy Class 8 Tractors Operating in Canada
GEM Input Name
Regulatory Subcategory Description
HC8 SC HR
Heavy Class 8 Combination, Sleeper Cab - High Roof
HC8 SC MR
Heavy Class 8 Combination, Sleeper Cab - Mid Roof
HC8 SC LR
Heavy Class 8 Combination, Sleeper Cab - Low Roof
HC8 DC HR
Heavy Class 8 Combination, Day Cab - High Roof
HC8 DC MR
Heavy Class 8 Combination, Day Cab - Mid Roof
HC8 DC LR
Heavy Class 8 Combination, Day Cab - Low Roof

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The next columns in the input file are for the engine and transmission file names or the
powertrain file name. A description of the content of these supplemental input files is located at
the end of this section. The text in the fields of the input file must exactly match the file name,
including the .csv extension for the code to run properly. In the Sample Input Files folder
provided with GEM, the supplemental files are located in separate Axle, Engine, Powertrain and
Transmission subfolders. GEM searches for the supplemental files from the same location as the
vehicle input file. As a result, the subfolder name must be included in the File Name fields, as
shown in Figure 17, to direct the model to the files. If users have their engine, transmission,
powertrain and axle files in the same folder as the vehicle input file, only the filename is needed.
Manufacturers may choose to perform powertrain testing to obtain the engine and
transmission performance for their GEM simulations. In order to indicate to GEM that
powertrain data is provided, users would provide the same powertrain input file name in both the
Engine and Transmission File Name fields of the tractor input file, as seen in the last row of
Figure 17.
Engine
Data
File Name
Engines\EPA_2018_D_GEN ERIC_455_CycleAvg.csv
Engines\EPA_2018_D_GEN ERIC_350_CycleAvg.csv
Engines\EPA_2018_D_GEN ERIC_600_CycleAvg.csv
Engines\EPA_2018_D_GEN ERIC_600_CycleAvg.csv
Engines\EPA_2018_D_GEN ERIC_455_CycleAvg.csv
Engines\EPA_2018_D_GEN ERIC_455_CycleAvg.csv
Engines\EPA_2018_D_GEN ERIC_455_CycleAvg.csv
Engines\EPA_2018_D_GEN ERIC_455_AIICycleAvg.csv
Powertrains\EPA_Sample_Powertrain.csv
Figure 17: Tractor Input File Reference to E
Transmission
Data
File Name
Transmissions\EPA_AMT_10_C78_4490.csv
Transmissions\EPA_AMT_10_C78_4490.csv
Transmissions\EPA_AMT_10_C78_4490.csv
Transmissions\EPA_MT_13_C78_4543.csv
Transmissions\EPA_AMT_10_C78_4490.csv
Transmissions\EPA_AT_10_C78_8001.csv
Transmissions\EPA_AMT_10_C78_4490_power_loss.csv
Transmissions\EPA_AMT_10_C78_4490.csv
Powertrains\EPA_Sample_Powertrain.csv
lgine, Transmission, and Powertrain Input Files
Figure 18 shows the next columns containing the tractor performance parameters and
several vehicle characteristics that are user-defined in GEM. A description of these parameters
was given in Table 8 and additional information is available in the preamble to the Phase 2
rulemaking. The Drive Axle Data File Name field points to the location and name of the
optional axle file. Note, if users do not use an optional axle file, then input "NA". The format of
this field is similar to the engine and transmission file fields shown in Figure 17. Note that for
tractors (second row) that have a single rear axle (i.e., 4x2 axle configuration), the users input an
"NA" into the Drive Axle 2 Tire Rolling Resistance Level field for those vehicles. Also, heavy-
haul tractors (third row) have a default Aerodynamic Drag Area (CdA) of 5.0 m2 within GEM, so
users also input an "NA" into that field for heavy-haul tractors.

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Drive Axle	Drive Axle Drive Axle	Aerodynamic Steer Axle Tire	Drive Axle ITire	Drive Axle 2Tire	Drive Axle Tire
Configuration Ratio	Data	AerodynamicDragArea (CdA) Rolling Resistance Level Rolling Resistance Level Rolling Resistance Level Loaded Tire Size
(e.g. 6x4)	# File Name	mA2 kg/t	kg/t kg/t	rev/mi
6x4	3.08 NA	5.4	6.9	6.9	6.9	500
4x2	3.42 NA	5.1	6.9	6.9 NA	500
6x4	3.23 NA	NA	6.9	6.9	6.9	500
6x4	3.12 NA	5.07	7	6.8	6.8	512
6x4	3.45 NA	5.35	6.9	6.9	6.9	500
6x4	3.45 NA	5.18	6.9	6.9	6.9	512
6x4D	3.12 Axles\EPA_Axle.csv	4.88	6.9	6.9	6.9	500
6x4	3.08 NA	5.4	6.9	6.9	6.9	500
6x4	3.08 NA	5.4	6.9	6.9	6.9	500
Figure 18: Tractor Input File Performance Parameters and User-Defined Vehicle Characteristics
There are limits associated with each user-defined input value. Drive Axle Configuration
is a text input and the allowable text is "6x4", "4x2", "6x4D", or "6x2". Vehicles with more
than two drive axles are instructed to use the "6x4" configuration in the model. All tractors with
"6x2" axle configurations are modeled with five axles with two steer tires, 4 non-drive tires and
4 drive tires. All tractors with "6x4" axle configurations are modeled with five axles with two
steer tires and eight drive tires. The only difference in GEM between "6x2" and "6x4" axles is
that there is an additional 1 percent loss for "6x4" axles to account for the inter-axle losses. All
tractors with "6x4D" axle configurations are modeled as "6x2" axles on the cruise cycles and
"6x4" axles on the transient cycle. All tractors with a "4x2" axle are represented by a four axle
tractor with two steer tires and four drive tires. Table 23 shows the limits for the remaining six
tractor inputs in the model. GEM will produce an error if any of these values are out of the
acceptable range and will round any values beyond their specified decimal limits.
Table 23: Minimum and Maximum Limits for User-Defined Values in Tractor Input File
User-Defined Parameter
Units
Number of
Decimals
Minimum
Value
Maximum
Value
Drive Axle Ratio
#
2
1.00
20.00
Aerodynamic Drag Area (CdA)
mA2
2
3.00
8.00
Steer Axle Tire, Rolling Resistance Level
kg/t
1
3.0
20.0
Drive Axle 1 Tire, Rolling Resistance Level
kg/t
1
3.0
20.0
Drive Axle 2 Tire, Rolling Resistance Level
kg/t
1
3.0
20.0 or NA
Drive Axle Loaded Tire Size
rev/mi
0
100
1000
The next columns in the tractor input file are for the optional technology improvements.
These technology improvement fields cannot be blank in the input file. The first three tractor
technology improvements, seen in Figure 19, will directly impact the vehicle simulation.
Vehicle speed limiters reduce the maximum allowable speed of the vehicle during the simulation
to the user-specified value. Weight reduction reduces the overall vehicle weight (and increases
payload) as noted in Table 7. If no weight reduction is used, then input "0". Neutral-idle
reduces the fuel consumption of the engine when a simulated automatic transmission vehicle is
idling. If the vehicle includes neutral-idle, then input "Y". If it does not include neutral-idle,
then input "N". The remaining technology improvements, shown in Figure 20, have specific
percent reductions that manufacturers will apply for the given technology fields. If the
technology improvement(s) is not applicable to the vehicle being simulated, then input "0". The

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Other field may be used for several technologies, including results from any off-cycle testing that
manufacturers may perform. See Table 9 and, generally, 40 CFR 1037.520 for the appropriate
percent values. All values of "Y", "N", or "NA" must be in UPPERCASE LETTERS.
Lowercase letters will produce an error.
Technology Improvement Technology Improvement Technology Improvement
Vehicle Speed Li miter Weight Reduction	Neutral-Idle
MPHorNA	lbs	Y/N
NA	ON
NA	100 N
NA	ON
NA	ON
NA	ON
NA	0 Y
NA	ON
NA	ON
NA	ON
Figure 19: Tractor Technology Improvements
Technology Improvement Technology Improvement Technology Improvement Technology Improvement Technology Improvement
Intelligent Controls	Accessory Load	Extended Idle Reduction Tire Pressure System Other
Figure 20: Tractor Technology Improvements with Pre-Defined Percent Improvements
Similar to the user-defined parameters, these technology improvements also have limits.
The format and limits for the technology improvements are shown in Table 24. Input values
with additional decimal places will be rounded to the appropriate precision. Input values outside
the minimum and maximum range specified will produce an error.
Table 24: Minimum and Maximum Limits for Technology Improvement Values in Tractor Input File
Modeling Parameter
Units
Number of
Decimals
Minimum
Maximum
Vehicle Speed Limiter
MPH or NA
1
54.0
65.0
Weight Reduction
lb
0
0
14,000
Neutral Idle, Automatic Transmissions Only
Y/N
-
-
-
Intelligent Controls
%
1
1.0
10.0
Accessory Load
%
1
1.0
10.0
Extended Idle Reduction, Sleeper Cabs Only
%
1
1.0
10.0
Tire Pressure System
%
1
1.0
10.0
Other
%
1
1.0
50.0

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IV.C. Vocational Input Files
The top of the vocational input file has three lines that list the regulatory category,
manufacturer name and model year (see Figure 21). The first line must read "Vocational" in
order for GEM to run the appropriate vehicle model. Manufacturer name can be in any format,
but it should be consistent with other regulatory documents from the manufacturer. Model year
should be expressed as a four-digit number.
The next lines of the vocational input file contain the model inputs. In the first two
columns, shown in Figure 22, the user provides a Run ID and the Regulatory Subcategory for
each run. The Run ID is a unique value that will be used to identify the run (e.g., vehicle VIN).
It can be any combination of letters, numbers and separators such as dash ("-"), periods ("."), or
underscores ("_"). The Regulatory Subcategory determines the vehicle that is modeled and the
standard that is applied for compliance. For vocational, there are nine standard regulatory
subcategories in GEM and Table 25 shows the naming convention. In addition, GEM includes
seven optional custom chassis vocational subcategories that represent vehicles that are designed
for specific operations. Manufacturers may optionally certify their vocational vehicles with
these custom chassis designations, using the naming convention shown in Table 26. See Section
V.B.2.b of the preamble to this rulemaking for a discussion of these optional custom chassis
subcategories.
Regulatory Category Vocational
Manufacturer Name EPA
Model Year
2018
Figure 21: Vocational Input File Header Information
Run ID
Unique Identifier
Sample_l
Sample_2
Sample_3
Sample_4
Sample_5
Sample_6
Sample_7
Sample_8
CC_Sample_l
CC_Sample_2
CC_Sample_3
CC_Sample_4
CC_Sample_5
CC_Sample_6
CC_Sample_7
PT_Samplel
Regulatory Subcategory
(e.g. HHD_R)
HHD_R
HHD_M
LHD_U
LHD_M
LHD_U
LHD_U
MHD_R
LHD_M
HHD_CC_RF
HHD_CC_EM
HHD_CC_CM
HHD_CC_OB
HHD_CC_CB
MHD_CC_MH
MHD_CC_SB
HHD_M
Figure 22: Vocational Input File Run ID and Regulatory Subcategory Inputs

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Table 25: Vocational Input File Naming Convention for Vocational Regulatory Subcategories
GEM Input Name
Regulatory Subcategory Description
HHD R
Heavy-Heavy Duty, Regional
HHD M
Heavy-Heavy Duty, Multipurpose
HHD U
Heavy-Heavy Duty, Urban
MHD R
Medium-Heavy Duty, Regional
MHD M
Medium-Heavy Duty, Multipurpose
MHD U
Medium-Heavy Duty, Urban
LHD R
Light-Heavy Duty, Regional
LHD M
Light-Heavy Duty, Multipurpose
LHD U
Light-Heavy Duty, Urban
Table 26: Vocational Input File Naming Convention for Vocational Regulatory Subcategories
GEM Input Name
Custom Chassis Subcategory Description
HHD CC EM
Emergency Vehicles
HHD CC CM
Cement Mixers and Other Mixed Use Applications
HHD CC RF
Refuse Vehicles
HHD CC CB
Coach Buses
HHD CC OB
Transit Bus, Other Bus and Drayage Tractors
MHD CC MH
Motor Homes
MHD CC SB
School Bus
The next columns in the input file are for the engine and transmission file names or the
powertrain file name. A description of the content of these supplemental input files is located at
the end of this section. The text in the fields of the input file must exactly match the file name,
including the .csv extension for the code to run properly. In the Sample Input Files folder
provided with GEM, the supplemental files are located in separate Axle, Engine, Powertrain and
Transmission subfolders. GEM searches for the supplemental files from the same location as the
vehicle input file. As a result, the subfolder name must be included in the File Name fields, as
shown in Figure 23, to direct the model to the files. If users have their engine, transmission,
powertrain and axle files in the same folder as the vehicle input file, only the filename is needed.
Manufacturers may choose to perform powertrain testing to obtain the engine and transmission
performance for their GEM simulations. In order to indicate to GEM that powertrain data is
provided, users would provide the same powertrain input file name in both the Engine and
Transmission File Name fields of the tractor input file, as seen in the last row of Figure 23. Note
that the custom chassis subcategories (rows 9-15 of the sample input file) use default engines and
transmissions within GEM and manufacturers input "NA" in those fields.

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Engine
Data
File Name
Engines\EPA_2018_D_GENERIC_350_CycleAvg.csv
Engines\EPA_2018_D_GENERIC_350_CycleAvg.csv
Engines\EPA_2018_D_GENERIC_200_CycleAvg.csv
Engines\EPA_2018_D_GENERIC_200_CycleAvg.csv
Engines\EPA_2018_D_GENERIC_200_CycleAvg.csv
Engines\EPA_2018_G_GENERIC_300hp_CycleAvg.csv
Engines\EPA_2018_D_GENERIC_270_CycleAvg.csv
Engines\EPA_2018_D_GENERIC_200_CycleAvg.csv
NA
NA
NA
NA
NA
NA
NA
Powertrains\EPA_Sample_Powert rain.csv
Transmission
Data
File Name
Transmissions\EPA_MT_10_HHD.csv
Transmissions\EPA_AT_5_HHD_LU3.csv
Transmissions\EPA_AT_6_LHD_LU3.csv
Transmissions\EPA_AT_6_LHD_LU3.csv
Transmissions\EPA_AT_6_LHD_LU2.csv
Transmissions\EPA_AT_6_LHD_LU2.csv
Transmissions\EPA_AT_6_MHD_LU3.csv
Transmissions\EPA_AT_6_LHD_LU3.csv
NA
NA
NA
NA
NA
NA
NA
Powertrains\EPA_Sample_Powertrain.csv
Figure 23: Vocational Input File Reference to Engine, Transmission, and Powertrain Input Files
The next columns of the sample input file are shown in Figure 24 and contain the
vocational performance parameters and vehicle characteristics that are user-defined in GEM. A
description of these parameters was given in Table 15 and additional information is available in
Section V.D of the preamble to the Phase 2 rulemaking. Note that for vehicles that have a single
rear axle (i.e., 4x2 axle configuration), the users input an "NA" into the Drive Axle 2 Tire
Rolling Resistance Level field for those vehicles. As shown in Figure 24, custom chassis
manufacturers only specify the drive axle configuration and tire rolling resistance values; all
other user-defined fields are marked "NA".
Drive Axle
Drive Axle Drive Axle
Aerodynamic Improvement (Delta) Steer Axle Tire
Drive Axle ITire
Drive Axle 2Tire
Drive Axle Tire
Configuration
Ratio
Data
Aerodynamic Dr
ag Area (CdA) Rolling Resistance Level Rolling Resistance Level Rolling Resistance Level Loaded Tire Size
(e.g. 6x4)
#
File Name
mA2
kg/t
kg/t
kg/t
rev/mi

6X4

3.73 NA

0
7.7
7.7
7.7
530
6X4D

4.33 Axles\EPA_Axle.csv

0
7.7
7.7
7.7
530
4x2

4.09 NA

0
6.2
6.2 NA

500
4x2

4.09 NA

0
6.2
6.2 NA

500
4x2

4.09 NA

0
6.2
6.2 NA

500
4x2

4.09 NA

0
6.2
6.2 NA

500
4x2

3.8 NA

0.2
6.2
6.2 NA

500
4x2

4.09 NA

0
6.2
6.2 NA

500
6X4
NA
NA
NA

7.7
7.4
7.4 NA

6X4
NA
NA
NA

7.3
7.1
7.1 NA

6X4
NA
NA
NA

7.7
7.7
7.7 NA

4x2
NA
NA
NA

7.7
6.9 NA
NA

6x2
NA
NA
NA

7.7
6.8
6.8 NA

4x2
NA
NA
NA

7.6
7.5 NA
NA

4x2
NA
NA
NA

7.7
7.7 NA
NA

6x4

3.54 NA

0
6.9
6.9
6.9
512
Figure 24: Vocational Input File Performance Parameters and User-Defined Vehicle Characteristics
There are limits associated with each user-defined input value. Drive Axle Configuration
is a text input and the allowable text is "6x4", "4x2", "6x4D", or "6x2". Vehicles with more
than two drive axles are instructed to use the "6x4" configuration in the model. All vehicles with
"6x2" axle configurations are modeled with five axles with two steer tires, 4 non-drive tires and
4 drive tires. All vehicles with "6x4" axle configurations are modeled with five axles with two
steer tires and eight drive tires. The only difference in GEM between "6x2" and "6x4" axles is
that there is an additional 1 percent loss for "6x4" axles to account for the inter-axle losses. All

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vehicles with "6x4D" axle configurations are modeled as "6x2" axles on the cruise cycles and
"6x4" axles on the transient cycle. All vehicles with a "4x2" axle are represented by a four axles
with two steer tires and four drive tires. The Drive Axle Data File Name field points to the
location and name of the optional axle file. The format of this field is similar to the engine and
transmission file fields shown in Figure 23. Table 27 shows the limits for the next six vocational
inputs in the model. GEM will produce an error if any of these values are out of the acceptable
range and will round any values beyond their specified decimal limits. Note that the
aerodynamic improvement for vocational vehicles is measured as a delta CdA and not the
absolute CdA value used in the tractor program.
Table 27: Minimum and Maximum Limits for User-Defined Values in Vocational Input File
User-Defined Parameter
Units
Number of
Decimals
Minimum
Value
Maximum
Value
Drive Axle Ratio
#
2
1.00
20.00
Aerodynamic Drag Area (Delta CdA)
mA2
2
0.00
4.00
Steer Axle Tire, Rolling Resistance Level
kg/t
1
3.0
20.0
Drive Axle 1 Tire, Rolling Resistance Level
kg/t
1
3.0
20.0
Drive Axle 2 Tire, Rolling Resistance Level
kg/t
1
3.0
20.0 or NA
Drive Axle Loaded Tire Size
rev/mi
0
100
1000
The next columns in the vocational input file are for the optional technology
improvements. These technology improvement fields cannot be blank in the input file. Five of
the next six vocational technology improvements, seen in Figure 25, will directly impact the
vehicle simulation. Vehicle speed limiters reduce the maximum allowable speed of the vehicle
during the simulation to the user-specified value. Weight reduction reduces the overall vehicle
weight (and increases payload) as noted in Table 14. Neutral-idle reduces fueling when a
simulated automatic transmission vehicle is idling, Start-Stop reduces fueling when the
simulation comes to a stop in the transient drive cycle and drive idle cycle, and Automatic
Engine Shutdown reduces fueling during the parked idle cycle. See preamble Section V.C. 1 .a.iv
for a description of the three workday idle reduction options. If the vocational vehicle will be
built with a hybrid power take-off (PTO) and testing was conducted according to 40 CFR
1037.540, then the Delta PTO value obtained from that test procedure may be entered. Please
note that these inputs are case-sensitive. All values of "Y", "N", or "NA" must be in
UPPERCASE LETTERS. Lowercase letters will produce an error.

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Technology Improvement Technology Improvement Technology Improvement Technology Improvement Technology Improvement Technology Improvement
Vehicle Speed Limiter Delta PTO Fuel
MPHorNA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
g/ton-mile
Weight Reduction
lbs
Neutral-Idle
Y/N
0 N
0 N
0 N
0 Y
0 N
0 Y
0 Y
0 Y
0 N
0 N
0 N
0 N
0 N
0 N
0 N
0 N
Start-Stop
Y/N
N
N
N
N
Y
N
N
N
N
N
N
N
N
N
N
N
Automatic Engine Shutdown
Y/N
Y
Y
N
N
Y
Y
N
N
N
N
N
N
N
N
N
Y
Figure 25: Vocational Technology Improvements
The remaining three technology improvements, shown in Figure 26, have specific percent
reductions that manufacturers will apply for the given technology fields. The Other field may be
used for several technologies, including results from any off-cycle testing that manufacturers
may perform. See Table 16 and, generally, 40 CFR 1037.520 for the appropriate percent values.
Technology Improvement Technology Improvement Technology Improvement
Accessory Load
Tire Pressure System
%
Other
Figure 26: Vocational Technology Improvements with Pre-Defined Percent Improvements
Similar to the user-defined parameters, these technology improvements also have limits.
The format and limits for the technology improvements are shown in Table 28. Input values
with additional decimal places will be rounded to the appropriate precision. Input values outside
the minimum and maximum range specified will produce an error.

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Table 28: Minimum and Maximum Limits for Technology Improvement Values in Vocational Input File
Modeling Parameter
Units
Number of
Decimals
Minimum
Maximum
Vehicle Speed Limiter
MPH or NA
1
54.0
65.0
Weight Reduction
lb
0
0
10,000
Delta PTO
g/ton-mi
3
0.000
3.000
Neutral Idle, Automatic Transmissions Only
Y/N
-
-
-
Start-Stop
Y/N
-
-
-
Automatic Engine Shutdown
Y/N
-
-
-
Accessory Load
%
1
1.0
10.0
Tire Pressure System
%
1
1.0
10.0
Other
%
1
1.0
50.0
IV.D. Trailer Input Files
The top of the trailer input file has three lines that list the regulatory category,
manufacturer name and model year (see Figure 27). The first line must read "Trailer" in order
for GEM to run the appropriate vehicle model. Manufacturer name can be in any format, but it
should be consistent with other regulatory documents from the manufacturer. Model year should
be expressed as a four-digit number.
Regulatory Category Trailer
Manufacturer Name EPA
Model Year	2018
Figure 27: Trailer Input File Header Information
The next lines of the trailer input file contain the model inputs. In the first two columns,
shown in Figure 28, the user provides a Run ID and the Regulatory Subcategory for each run.
The Run ID is a unique value that will be used to identify the run. It can be any combination of
letters, numbers and separators such as dash periods or underscores	The
Regulatory Subcategory determines which standard is applied for compliance. For trailers, there
are four regulatory subcategories modeled in GEM and Table 29 shows the naming convention.
While the trailer program does include reduced standards for some trailer types, trailer
manufacturers do not use GEM for compliance and we did not configure GEM with additional
subcategories for those trailers. These four vehicles are sufficient to create the GEM-based
equation used in trailer compliance.
Run ID	Regulatory Subcategory
Unique Identifier	(e.g. LDV)
LDV_1	LDV
LRV_1	LRV
SDV_1	SDV
SRV 1	SRV
Figure 28: Trailer Input File Run ID and Regulatory Subcategory Inputs

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Table 29: Trailer Input File Naming Convention for Trailer Regulatory Subcategory Inputs
GEM Input Name
Regulatory Subcategory Description
LDV
Long Dry Van
LRV
Long Refrigerated Van
SDV
Short Dry Van
SRV
Short Refrigerated Van
The next columns contain the trailer performance parameters and technology
improvement options that are user-defined in GEM. A description of these parameters was given
in Table 20 and additional information is available preamble to the Phase 2 rulemaking. Note
that the aerodynamic improvement for trailers is measured as a delta CdA and not the absolute
CdA value used in the tractor program.
Aerodynamic Improvement (Delta) TrailerTire	Technology Improvement Technology Improvement
Aerodynamic Drag Area (CdA)	Rolling Resistance Level Weight Reduction	Tire Pressure System
mA2	kg/t	lbs	%
0	6	0	0
0	6	0	0
0	6	0	0
0	6	0	0
Figure 29: Trailer Input File Performance Parameters and User-Defined Vehicle Characteristics
There are limits associated with the user-defined and technology improvement input
values as shown in Table 30. GEM will produce an error if the fields are blank or if any of these
values are out of the acceptable range. Users that wish to model their vehicle with weight
reduction can enter the cumulative weight reduction value (0 to 5,000 lbs or "NA"). The tire
pressure system is a set percent value for use of an automatic tire inflation system or a tire
pressure monitoring system. See 40 CFR 1037.515, noting that the ATIS and TPMS values
listed in the regulation are in decimal format, because trailers will use a GEM-based equation for
compliance.
Table 30: Minimum and Maximum Limits of Technology Improvements in Trailer Input File
User-Defined Parameter
Units
Minimum
Value
Maximum
Value
Aerodynamic Drag Area (CdA)
m2
0
4
Tire Rolling Resistance Level (TRRL)
kg/t
3
20
Weight Reduction
lbs
0
5000
Tire Pressure System
%
0
10

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IV.E. Supplemental Input Files
As mentioned previously, the GEM installation package contains sample input files,
including four folders of supplemental input files, as follows:
	Axles: one example axle definition file
	Engines: 13 example steady-state and cycle average engine definition files
	Powertrains: one an example powertrain definition file
	Transmissions: 11 example transmission definition files
IV.E.l. Engine Input File for Tractor and Vocational Vehicles
Tractor and vocational vehicle manufacturers are required to generate separate engine
and transmission input files, or, optionally, a single powertrain input file for GEM. A vehicle
manufacturer would generate a separate engine and transmission file for each engine and
transmission used in its vehicles, or separate powertrain files for each engine and transmission
combination tested. The transmission input file may optionally contain transmission power loss
data. The axle input file is optional for manufacturers that would like to include more axle loss
information. These files must be in .csv format to be properly read by the model. Each
supplemental file consists of multiple tables that must be separated by an empty row to be
processed correctly. We recommend that the manufacturers choose a consistent naming
convention that provides unique file names for each of these supplemental input files. Note that
trailer manufacturers do not have the option to use these supplemental input files and instead rely
on default values built into the trailer model. The first row of the GEM input file for engines
shows the GEM version, and the fourth row contains user-specified Manufacturer Name,
Combustion Type, Fuel Type, Family Name, Calibration ID, Declared Engine Idle Speed as
defined in 40 CFR 1036.510, and Displacement, as shown in Figure 30. Combustion Type and
Fuel Type have specific options for a manufacturer to choose. The user can choose any name for
the other header fields, but the names should be consistent with other regulatory documents from
the manufacturer.
GEM P2v3.0 Engine Definition
Manufacturer Name	CombustionType	FuelType	Family Name	Calibration ID Idle Speed at CITT Displacement
(e.g. Cummins)	(Compression Ignition / Spark Ignition)	(Diesel / Gasoline / LNG/CNG)	(e.g. abcdl2345efg) (e.g. 123abc) RPM	liters
EPA	Compression Ignition	Diesel	GENERIC	1	750	7
Figure 30: Sample Engine Input File Header Information
The manufacturer then specifies engine information in five separate comma-separated
tables, as shown in Figure 31. The first table is the engine full-load torque curve, followed by
the parent engine full load torque curve and the engine motoring torque curve. Torque curves
are specified in RPM and Nm, and procedures for producing the torque curves, including the
number of speed and torque points to measure, are specified in 40 CFR 1065.510. The next
tables are the four-point engine idle fuel map and the steady-state engine fuel map. The speed,
torque, and fuel rate in the fuel maps are specified in RPM, Nm, and g/s, respectively.
Procedures for generating the idle and full engine fuel maps are specified in 40 CFR 1036.535
and 1065.510.

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Engine Full Load Torque Curve
Speed	Torque
RPM	Nm
750
907
440
580
Parent Engine Full Load Torque Curve
Speed	Torque
RPM	Nm
750
907
440
580
Engine MotoringTorque Curve
Speed	Torque
RPM	Nm
750
907
-129.17
-129.19198
Engine Idle Fuel Map
Speed
RPM
Torque
Nm
750
850
750
850
Fuel Rate
grams/sec
0
0
100
100
0.258210373
0.261284511
0.689671498
0.726963355
Engine Fuel Map
Speed
RPM
Torque
Nm
750
750
Fuel Rate
grams/sec
-188.98472
-170.2299298
Figure 31: Sample Engine Input File Engine Characteristics
The engine input file described so far includes all of the steady-state fuel map
information needed to run GEM. However, tractor and vocational vehicle manufacturers must
include a cycle average fuel map for the transient cycle, and can optionally apply cycle averaging
to the 55- and 65-mph cruise cycles for compliance. Cycle average maps are added to the
bottom of the engine input file, following the steady-state fuel map. Section VI.A. 1 of this
Guide describes the procedure to generate cycle average maps.
Figure 32 shows the information and format of the transient cycle average fuel map
added to the engine input file below the steady-state engine fuel map. Similar tables can be
added below the transient map for the cruise cycles using the appropriate headings (i.e., "55
MPH Cruise Cycle Average Fuel Map" or "65 MPH Cruise Cycle Average Fuel Map"). This
new engine input file with cycle averaged results can now be used for compliance. Instructions
for generating the information needed for the cycle average tables can be found in Section
VI.A. 1. Note that GEM will generate an error for tractor and vocational vehicles if the Transient
Cycle Average Fuel Map information is missing in the engine input file.

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Transient Cycle Average Fuel Map
Engine Cycle Work	Simulation N/V	Fuel Mass
kWh	rev/m	grams
3.341302	2.318	914.8755
5.329391	2.5176	1355.6025
Figure 32: Cycle Average Fuel Map Table in the Engine Input File
IV.E.2. Transmission Input File for Tractor and Vocational Vehicles
The first row of the GEM input file for transmissions shows the GEM version, and
manufacturers would fill in the fifth row with the transmission's Manufacturer Name, Type, and
Model Name (see Figure 33). The vehicle manufacturer can choose any Manufacturer Name and
Model Name for the transmission, but it should remain consistent with other regulatory
documents. The transmission Type has specific options for the manufacturer to choose.
GEM P2v3.0Transmission Definition
Manufacturer Name	Type	Model Name
(e.g. Eaton)	(AMT/ MT/ AT) (e.g. 7100)
EPA	AMT	HHD
Figure 33: Sample Transmission Input File Header Information
If the transmission is an automatic transmission that has a lockup gear other than the one
programmed in the GEM shift strategy, an additional column can be added to specify the
minimum lockup gear. This column is not required and GEM will use a third-gear lockup for
automatic transmissions by default. Lockup does not apply for AMT and manual transmissions.
The optional additional transmission header information for automatic transmissions is shown in
Figure 34.
Manufacturer Name	Type	Model Name Minimum Lockup Gear
(e.g. Eaton)	(AMT/MT/AT) (e.g. 7100)	Number/NA
EPA	AT	HHD	3
Figure 34: Sample (Optional) Transmission Input File Header Information for Automatic Transmissions
Vehicle manufacturers provide the gear ratios for their specific transmission, as seen in
the sample shown in Figure 35. If engine torque is limited when operating in a particular gear it
should be entered in the appropriate column.

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Transmission Gears
GearNumber	GearRatio	Input Torque Limit
#	#	Nm
1	12.8	2300
2	9.25	2300
Figure 35: Sample Transmission Input File Transmission Gear Ratio Information
Manufactures can optionally include transmission power loss information in their
transmission input file. Instructions for obtaining this information is found in 40 CFR 1037.565.
The format of the power loss table is shown in Figure 36. When providing power loss
information not all gears need to be included. Neutral is always optional. If loss information is
provided for a given gear all higher gears must also be included.
Transmission Power Loss
GearNumber	InputSpeed	InputTorque	Power Loss
#	RPM	Nm	kW
0	600	0 0.5023
0	1200	0 1.3559
Figure 36: Sample Transmission Input File (Optional) Transmission Power Loss Information
IV.E.3. Optional Powertrain Input File for Tractor and Vocational Vehicles
Users may opt to use engine and transmission performance data obtained from a
powertrain test in their GEM runs. Procedures for generating the data to populate a powertrain
input file can be found in 40 CFR 1037.550. This section summarizes the input file format.
The first row of the GEM input file from powertrain testing show the GEM version and
manufacturers would fill in the fifth, ninth, and thirteenth rows with the relevant information
about the engine, transmission and powertrain, respectively. Figure 37 shows the header
information required by the model.
GEM Pcwertrairi Definition
Engine Manufacturer Name	Combustion Type
(e.g. Cummins)	(Compression Ignition / Spark Ignition)
Cummins	Compression Ignition
Transmission Manufacturer Name Type
(e.g. Eaton)	(AMT / MT / AT / DCT)
Eaton	AMT
Fuel Type	Family Name	Calibration ID
(Diesel / Gasoline / LNG / CNG) (e.g. abcd12345efg) (e.g. 123abc)
Diesel	' ISX	CAL1
Gears	Model Name
Number	(e.g. 7100)
10 ULTRASHIFT13LAS
Powertrain Family Name	Calibration ID	Powertrain Test Configuration
(e.g. abcd12345efg)	(e.g. 123abc)	(1: Trans. Output. 2: Wheel Hubs)
SmartAdvantage	CAL1	1
Figure 37: Sample Powertrain Input File Header Information

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The next rows of the powertrain input file, as seen in Figure 38, include the engine idle
fuel rate and the powertrain performance information from the 55-MPH, 65-MPH, and Transient
drive cycle tests. Users would supply the cycle work, output speed/vehicle speed, and fuel mass
according to the procedures outlined in 40 CFR 1037.550(o).
Engine Idle Fuel Rate
grams / sec
0.576
55 MPH Cruise
Powertrain Cycle Work N/V	Fuel Mass
kWh	rev / meter	grams
25.28	0.86	5031
25 25	0.93	5050
18.85	1.00	3845
65 MPH Cruise
Powertrain Cycle Work	N/V	Fuel Mass
kWh	rev / meter	grams
29.49	0.86	5780
29.62	0.93	5865
21.32	1.00	4371
Transient
Powertrain Cycle Work N/V	Fuel Mass
kWh	rev / meter	grams
8.28	0.86	2012
6.41	0.93	2027
8.01	1.00	1930
Figure 38: Sample Powertrain Input File Performance Information
IV.E.4. Optional Axle Input File for Tractor and Vocational Vehicles
The first row of the GEM input file for axles shows the GEM version, and the fourth row
contains user-specified Manufacturer Name, Family Name, and Type, as shown in Figure 39.
The user can type any text in the first two fields, but the names should be consistent with other
regulatory documents from the manufacturer. The valid options for axle type are "SINGLE",
"TANDEM" and "TANDEM WITH DISCONNECT".

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GEM P2v3.0Axle Definition
Manufacturer Name	Family Name	Type
(e.g. Dana)	(e.g. abcdl2345efg)
EPA	EPA	TANDEM WITH DISCONNECT
Figure 39: Sample Axle Input File Header Information
The next rows contain two comma separated tables for Axle Loss and Disconnect Axle
Loss, as shown in Figure 40. Each table includes output speed in RPM, output torque in Nm,
and power loss in kW. See 40 CFR 1037.560 for the test procedure to map axle efficiency and
determine appropriate values for this input file's tables. The disconnect axle losses are only
included by axles of type "TANDEM WITH DISCONNECT".
Axle Loss
OutputSpeed	OutputTorque Power Loss
RPM	Nm	kW
100	0	1.379
100	725	1.5638
100	2900	2.1181
Disconnect Axle Loss
OutputSpeed	OutputTorque Power Loss
RPM	Nm	kW
100	0	1.0835
100	725	1.2309
Figure 40: Sample Axle Loss Table in Axle Input File
V. GEM Output File Structure
An output file will be generated when the vehicle simulation completes and it is
automatically saved to the same location as the input file. When users run GEM from the Start
Menu or command prompt, the output file name will be given the same name as the input file
with a " result.csv" appended. During the simulation an error log file will be generated, even if
there are no errors, with the same base name as the input file with an "_errors.txt" extension.
Identical output files are generated for each of the methods.
V.A. Standard GEM Outputs for Compliance
Each output file is identical to the input file for the vehicle modeled, except that
additional columns of the .csv file are populated with the model's results. Figure 41 shows the
standard results of an example simulation. These results fields are the same for each vehicle
type, but their column location in the file varies. The first result column indicates the date and

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time when the simulation was performed. The next two columns are the raw GEM CO2
emissions and fuel consumption values. The next two columns are the Family Emissions Limit
(FEL) values EPA and NHTSA will use for compliance. EPA's FEL CO2 results are integer
values for vocational vehicles and trailers, and reported with a single decimal place precision for
tractors. NHTSA's fuel consumption results are calculated from those CO2 values, and are
reported with four decimal place precision for vocational vehicles and trailers, and five decimal
place precision for tractors to ensure consistency between the agencies' results.
Date/Time of Run	GEM C02 Emissions GEM Consumption FELC02 Emissions FELConsumption Subfamily Subfamily FEL Subfamily Volume
YYYY_MMDD_HHMMSS	g C02/ton-mile gal/lOOOton-mile g C02/ton-mile gal/1000 ton-mile Name g C02/ton-mile #
2016-071915:20:39	222.0614119 21.81349822 222	21.8075
2016-071915:20:51	284.345287 27.93175708 284	27.8978
2016-071915:21:00	454.7105 44.66704322 455	44.6955
2016-071915:21:10	361.3490975 35.49598207 361	35.4617
Figure 41: Example Vocational Results Columns in GEM Output File
The final three columns of the output file are left blank by the model. Manufacturers
would manually add the appropriate subfamily name, target FEL for the given subfamily, and the
volume of vehicles that will use the resulting FEL value prior to submitting their output file for
compliance.
V.B. Optional GEM Outputs for Cycle-Specific Information
Users that run GEM using the command prompt can generate additional, cycle-specific
information in their output files using the "-d" option (see Section VI.C for instructions). This
option adds 10 columns to the output file for each drive cycle (i.e., Cruise 55, Cruise 65, and
Transient), a column showing the final payload (which may have been adjusted if weight
reduction was included), and eight columns with additional information from the idle cycle
calculations.
Figure 42 shows the additional output for the 55-mph cruise cycle. The data includes
crankshaft average speed (RPM), average torque (Nm), and N/V (rev/m), positive work from the
crankshaft, transmission, and axle (all in kWh), fuel consumed (g) and emissions (g CO2 and g
CCh/ton-mile), and shift count. Similar information is added in separate columns for the 65-mph
cruise and transient cycles.
Cruise 55	Cruise 55	Cruise 55	Cruise 55	Cruise 55	Cruise 55 Cruise 55	Cruise 55 Cruise 55	Cruise 55
Crankshaft Avg Speed CrankshaftAvgTorque Crankshaft N/V Crankshaft Pos Work Transmission Pos Work AxlePosWork FuelConsumed Emissions Emissions ShiftCount
RPM	Nm	rev/m	kWh	kWh	kWh	g	gC02	gC02/ton-mile #
1263.7	948.4777	0.8598	30.75897075	28.9571046 26.71842053	5816.57 18787.79029 73.63497457	0
1264.1 970.3373 0.8598 31.46975037 29.6252395 27.33378739 5947.3 19210.03437 75.2892152 0
1265.8	905.4314	0.8598	29.36303669	27.58762017 25.38339982	5578.52 18018.87222 70.62116538	0
Figure 42: Additional Cycle-Specific Output for the Drive Cycles
Figure 43 shows the additional output for the idle cycles. The first idle data set includes
payload weight (tons), and non-idle emissions (g CCh/mile and g CCh/ton-mile). The next idle
data set includes in-gear idle crankshaft average speed (RPM) and average torque (Nm), neutral

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idle crankshaft average speed (RPM) and average torque (Nm), and total drive idle and parked
idle emission rates (g CCh/hr).
Payload Non Idle Weighted Non Idle Weighted
Weight Carbon Emissions Carbon Emissions
tons gC02/mile	g C02/ton-mile
19	1668.684616	87.82550609
19	1713.681791	90.19377845
19	1595.404923	83.96868014
In Gear Idle	In Gear Idle	Neutral Idle	Neutral Idle	Drive Idle	Parked Idle
Crankshaft Avg Speed Crankshaft AvgTorque CrankshaftAvgSpeed CrankshaftAvgTorque Carbon Emissions Carbon Emissions
RPM	Nm	RPM	Nm	gC02/hr	gC02/hr
599.9999993	55.70423015	599.9999993	55.70423015	5162.08136	5162.08136
599.9999993	55.70423015	599.9999993	55.70423015	5162.08136	5162.08136
599.9999993	55.70423015	599.9999993	55.70423015	5162.08136	5162.08136
Figure 43: Additional Cycle-Specific Output for the Idle Cycles
VI. Running GEM
There are two options for running GEM. The first option directly accesses the program's
executable file via the Start Menu folders, the Start Menu search, or a GEM icon on the
computer's desktop screen. This first option initiates a GEM pop-up window to select an input
file and run the model. The second option uses the command prompt, which will similarly
initiate GEM, but also has several options to generate additional output information. Each of
these options is described in the following sections.
VI.A. Preparing for GEM Runs
Prior to running GEM, it is important to locate all of the necessary input files. Many
computers will produce warnings if the users try to make changes to files in the installation
folder if it is located in the C:\Program Files directory. It is recommended that users save a copy
of the input file templates from the installation folder (i.e., C:\Program Files\US EPAVPhase 2
GEM\Sample Input Files - RELOCATE BEFORE USE) to a location on their hard drive (e.g.,
C:\Documents and Settings\UserName\My Documents). These files can then be changed as
needed to reflect the users' specific vehicles. See the previous sections for a description of the
input files.
VI.A.1. Cycle Average Fuel Map for Tractor and Vocational Vehicles
Tractor and vocational vehicle manufacturers must include a cycle average fuel map for
the transient cycle, and can optionally apply cycle average fuel maps to the 55 and 65 mph cruise
cycles in their engine input file. The procedure to generate a cycle average map is the same for
the transient and cruise cycles, except if the cycle average fuel map is used for the cruise cycles,
the steady-state fuel map will not be the steady-state fuel map of the engine but will be a default
fuel map with the idle portions of the fuel map from the engine. The final engine fuel map input
if only the cycle average procedures is used will contain the default steady-state fuel map where
the idle fuel rates are from the engine, the engine idle fuel map (for engines going into vocational
vehicles) and the cycle average fuel map for each of the three vehicle duty cycles.
Included in this GEM installation package are two sample vehicle input files that serve as
an example of the inputs needed to create the cycle average map:
1.	"GEM tractor EnginePrep inputs.csv" for tractor vehicles, and
2.	"GEM vocational EnginePrep inputs.csv" for vocational vehicles

-------
These input files rely on steady-state engine input files located in the sample subfolder
"Engines" and transmission input files located in the subfolder "Transmissions". Note that the
sample axle file is not used when creating the cycle average map. Typing NA in the axle input
column will trigger the default axle losses to be used.
Each engine is simulated in GEM with six, eight, or nine predefined vehicle
configurations depending on the vehicle class(s) that may use the engine. Engines used in
heavy-haul tractors are evaluated over six specific heavy-haul and sleeper cab configurations.
Engines that will be installed in vocational vehicles qualifying as Light HDV or Medium HDV
are evaluated over eight light- and medium-heavy duty configurations. Engines that will be
installed in vocational vehicles qualifying as Heavy HDV and for tractors that are not heavy-haul
tractors are evaluated over nine day cab and sleeper cab configurations. See the EnginePrep
example files for the appropriate default values to apply. To generate an engine file for
compliance and testing, manufacturers will supply their own steady-state engine input file except
in the case where a manufacturer is using the cycle average mapping procedure for the cruise
cycles and update the EnginePrep input file with the axle ratios and tire sizes that are calculated
from the engine's torque curve and the equations defined in 40 CFR 1036.540. Note for engines
that will be installed in vocational vehicles qualifying as Heavy HDV and for tractors the
transmission and ratios and are different between the cruise cycles and the transient cycle, so
separate GEM runs will have to be performed to create a cycle average fuel map for the cruise
cycle.
The EnginePrep input files are used with the GEM executable (i.e., the "Phase 2 GEM
Cycle Creation" executable from the Start Menu, or the "-e" option with the command prompt as
described in Sections VI.B and VI.C) to generate three engine cycle files in .csv format
corresponding to the transient, 55-mph, and 65-mph drive cycles. These output files are named
with the text of the unique identifier of the simulation followed by the drive cycle (e.g.,
"EngineXYZ_cyclel_transient_cycle.csv"). The .csv files include the average vehicle speed over
the drive cycle and three columns defining the engine cycle: Time (sec), Engine Speed (RPM)
and Engine Torque (Nm).
The engine cycle files are then used to test the actual engine according to 40 CFR 1065 to
generate the following results that will be added to the end of the steady-state fuel map file with
the appropriate headers, as described previously in Section IV:
1)	N/V Ratio (rev/meter) calculated from time average engine speed during engine test
divided by average vehicle speed from the generated cycle. Note that the average
vehicle speed is determined by GEM and is located in the GEM output file containing
the engine cycle.
2)	Positive cycle work (kWh) calculated from the engine test
3)	Total fuel mass for the test corrected for mass-specific net energy content of the fuel,
according to 40CFR 1036.540.
VI.A.2.Testing Input Files for Errors
Prior to running a GEM simulation, it is recommended that users test their input files for
errors. GEM will check that data are included in the required input file fields, file headers and

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data are in the proper format, and supplemental input files exist with the appropriate information.
Note that GEM is case-sensitive and will produce an error if inputs do not exactly match.
To test an input file, initiate the "Phase 2 GEM Check Inputs" executable from the Start
Menu, or use the "-t" option with the command prompt. Sections VI.B and VI.C describe how to
access the executable in the Start Menu and through the command prompt. GEM will run
through each line of the input file and search for errors. Figure 44 shows the status window that
appears when checking for errors. The status bar will progress as GEM checks each Run ID and
indicate "FAIL!" or "Input Valid!" Users can close this window and check the output files for
more information.
Processing Run ID Sample_1
Processing Run ID Sample_2
Processing Run ID Sample_3
Processing Run ID Sample_4
Processing Run ID Sample_5
Processing Run ID Sample_6
Processing Run ID Sample 7
.FAIL!
FAIL!
.FAIL!
.FAIL!
FAIL!
....Input Valid!
65% WITH 5 ERRORS!
Figure 44: Status Window Checking a GEM Input File for Errors
Once an input test ends (by completing the check or after being terminated by the user),
the two standard result.csv and _errors.txt files are created. The results file will simply display
if the inputs were valid or produced an error, as shown in Figure 45. Users are instructed to see
the error file for details.
Regulatory Category
Manufacturer Name
Model Year
GEM Version
Run ID
Unique Identifier
Sample_l- ERROR: see error file for details!
Sample_2~ ERROR: see error file for details!
Sample_3~ ERROR: see error file for details!
Sample_4- ERROR: see error file for details!
Sample_5~ ERROR: see error file for details!
Sample_6~ Input Validated
Sample_7- ERROR: see error file for details!
Sample_8- ERROR: see error file for details!
PT_Samplel~ Input Validated
Figure 45: Example Results.csv Output File Generated when Testing GEM Inputs
The error output file provides more information about each error. Figure 46 shows the
errors from this example. In Sample 1 and Sample 2, the engine and transmission file names
were provided, but the user did not indicate that they were located in subfolders, as noted
previously in the GEM Input File Structure sections. Sample 3 attempted to provide a CdA

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value for a heavy-haul tractor (i.e., regulatory subcategory "C8_HH"), but this subcategory has a
default value and the input should be "NA", The remaining errors indicated that the cases were
out of their allowable ranges.
QCElffl
File Edit Format View Help
|us EPA Phase 2 gem v3.0 Error Log
Sample_l  Invalid Engine Definition File C:\Users\jbrakora\Documents\MATLAB\GEM\2016.07.13 3.0 pre\Sample Input Files\EPA_2018_D_GENERlC_455_CycleAvg. csv - Unable to Open File
sample_2 -- invalid Transmission Definition File c:\users\jbrakora\Documents\MATLAB\GEM\2016.07.13 3.0 pre\sample input Files\EPA_AMT_10_c78_4490.csv - unable to open file
sample_3  invalid Aerodynamic Drag Area (CdA) should be na for C8_HH subcategory
5ample_4  invalid steer Axle Tire Rolling Resistance Level value "30" outside of allowable range ( 3.0 - 20.0 )
sample_5  invalid Loaded Tire speed value "1001" outside of allowable range ( 100 - 1000 )
sample_7  invalid Technology improvement weight Reduction value "20000" outside of allowable range CO- 14000 )
sample_8  invalid Technology improvement vehicle speed Limiter value "50" outside of allowable range ( 54.0 - 65.0 )
Figure 46: Example _Errors.txt Output File Generated when Testing GEM Inputs
Users should correct any errors in their files and rerun the test until they receive a
confirmation that all of the inputs are valid, as seen in Figure 47. Once completed, the input files
are now ready to be used in a GEM simulation.
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Processing Run ID Sample 5	
...Input Valid!

Processing Run ID Sample 6	
...Input Valid!

Processing Run ID Sample 7	
...Input Valid

Processing Run ID Sample 8	
...Input Valid!
	
Processing Run D PT Samplel
Input Valid!
-
 Batch Simulation Complete! 

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Figure 47: Status Window Indicating GEM Input Files Contain No Errors
VLB. Running GEM Using the Start Menu and Desktop Icon
Users can access the Phase 2 GEM executable from the Start Menu. Go to All Programs
> EPA Phase 2 GEM > Phase 2 GEM as shown in Figure 48. Note that this is the same location
of the executables to test input files ("Phase 2 GEM Check Inputs") and create cycle average
maps ("Phase 2 GEM Cycle Creation").

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Activldentity
AMD Catalyst Control Center
. Cisco
Cisco IPTV Viewer
Embedded Lockdown Manager
EndNote
, EPA Phase 2 GEM
ft Phase 2 GEM Check Inputs
Phase 2 GEM Cycle Creation
Phase 2 GEM Documentation
yjr Phase 2 GEM on the Web
Phase 2 GEM Sample Input
-V Phase 2 GEM User Guide
-ft; Phase 2 GEM	
Games
GIS (Mapping)
. Java
Juniper Networks
Lotus Applications
Maintenance
i Back
I Search programs and files
Figure 48: How to Access Phase 2 GEM from the Start Menu
Alternatively, users can access the executable by typing "Phase 2 GEM" in the Search
programs and files box located at the bottom of the Start Menu, and hitting "Enter". Users that
selected the option to "Create Desktop Icon" during installation can double click the icon (shown
previously in Figure 6) to initiate the program as well. Once the executable is selected, users will
briefly see the image shown in Figure 49 as the program loads.
W
GREENHOUSE GAS EMISSIONS MODEL
GEM P2V3.0
Figure 49: GEM Splash Screen as Program Loads
A pop-up window will ask the user to select an input file, as shown in Figure 50. By
default, the program will first look in the installation folder. As mentioned previously, all of the
input files should be moved to a separate location to avoid permissions warnings. In this
example, we moved the files to the Desktop and renamed the folder GEM P2 Sample Input Files.
Navigate to the input files folder, and select the appropriate input file
(GEM Sample TRACTOR csv in Figure 51) to begin the simulation.

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Figure 52: Sample Status Window Showing Progress of GEM Simulations

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The status window will indicate when the simulations are complete with a window
similar to Figure 53. The resulting output file will be saved in the same location as the input file,
and will be given the same name as the input file with a " result.csv" extension added to the end
("GEMSampleTRACTORresult.csv" in this example). When the simulation is complete,
users can close the status window by clicking the red "X" in the top right corner of the window.
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Figure 53: Sample Status Window Showing Complete GEM Simulations
This first example simulation completed without any errors. No errors were produced in
the status window or the error log, shown in Figure 54, provides confirmation. If an error occurs
in any simulations, the window will indicate the configurations that failed and the model will
continue to the next simulation. See Section VI. A.2 of this Guide for examples of errors and a
description of the _errors.txt file produced.
File Edit Format View Help
US EPA Phase 2 GEM v3.0 Error Log
Figure 54: Sample Error Log with No Errors from Simulation
VI.C. Running GEM Using the Command Prompt
Users can also initiate GEM using the command prompt. As seen in Figure 55, the
command prompt can be found using the Start Menu's Search programs andfiles feature. Once
the executable cmd.exe is selected, a command window similar to the one shown in Figure 56
will display.

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Programs (1)
SB cmd
See more results
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Figure 55: Initiating the Command Prompt from the Start Menu Search Bar
j C:\windows\systerri32\cmd.exe
icrosoft Windows [Uersion 6.1.7601]
opyright  2009 Microsoft Corporation. All rights reserved.
):\Users\UserName >_
Figure 56: Windows Command Prompt Window
Users begin by navigating to the installation directory where the GEM executable is
located using the command: cd "C: Program Files' USEPA\Phase 2 GEM. Users can then
initiate the same "Select an Input File" pop-up window shown in Figure 50 by typing the
command: GEM.exe as seen in Figure 57. Users follow the same steps to locate and select
an input file as shown in the previous section and GEM will show the GEM status window
similar to Figure 52.

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Microsoft Windows [Uersion 6.1.7601]
Copyright  2009 Microsoft Corporation. All rights reserved.
C:\UsersNUserName>cd C:\Progran FilesNUS EPANPhase 2 GEM
C:\Program FilesNUS EPANPhase 2 GEM>GEM.exe ""
C:\Progran FilesNUS EPANPhase 2 GEM>_
Figure 57: Command Prompt to Initiate GEM Input File Selection Pop-up Window
Alternatively, users have the option of bypassing use of the input file selection window
by including the location and name of the input file (GEM.exe "Path\Filename "), as shown in
Figure 58. In this example, the executable is stored in the default Program Files location and the
input files are located in a folder on the desktop. The program will directly initiate a status
window similar to Figure 52.

icrosoft Windows [Uersion 6.1.7601]
opyright (c) 2009 Microsoft Corporation.
All rights reserved.
:\Users\UserName>cd C:\Program FilesNUS EPANPhase 2 GEM
C:\Program FilesNUS EPANPhase 2 GEM>GEM.exe "C:\Users\UserName\Desktop\GEM P2 Sa
mple Input Files\GEM_tractor_sample_inputs.csv"
C:\Program FilesNUS EPANPhase 2 GEM>
Figure 58: Command Prompt to Initiate GEM and Directly Apply Input Files (no File Selection Window)
As mentioned previously, the command prompt method of running GEM has several
options that can alter the output format or generate additional data. These options are included
after the main command as single-letter flags with a dash (e.g., GEM.exe "Path\Filename" -t)
and users may include more than one flag in a single command. The available flags are shown in
Table 31. As mentioned previously, the -e flag is used to generate the cycle average maps
(Section VIA. 1) and the -t flag is used to test the input files prior to running GEM (Section
VI.A.2).

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Table 31: Command Line Options for GEM
Command Flag
Option Name
Description
-vN
Model output verbosity
N = 0 (default) logs only the data required for certification
N = 1 turns on the model's energy auditing
N = 2 or 3 add additional signals of interest for debugging.
-d
Detailed output
Generates additional cycle-specific data columns in the results.csv
file (see Section V.B)
-P
Preserve files
Preserve the simulation raw output as a .mat file for later
examination
-t
Test inputs
Disables simulation but allows the user to test the input file for
errors such as out of range parameters (see Section VI. A.2)
-n
No tech improvements
Turns off all technology improvements and result modifiers
-i
Save model inputs
Exports the model parameters before simulation; useful for later
running Simulink version.
-c
Console Only
Disables the status display window and runs in a console mode
-e
Engine cycle generation
Exports the engine speed and load data from each simulation of
each phase to a separate file for use in cycle average testing (see
Section VI. A. 1)
-s
Stringency mode
Bypasses requirement of cycle average map for ARB transient cycle
and rounding of input parameters is disabled.
This Guide does not provide examples of the use of each flag listed in Table 31.
However, the console option may be of interest to users who wish to automate their GEM runs.
As seen in Figure 59, when users apply the -c flag, the output generally shown in the GEM
status window is displayed in the command window instead.
I
Figure 59: Command Prompt Display When Using the Console Only Option
VII. Final Notes
Users are encouraged to look through the additional information provided in the
Documentation folder included with the GEM installation. For more information on the Phase 2
rule, please see Docket EPA-HQ-OAR-2014-0827 available at www.regulations.gov.
icrosoft Uindous [Uersion 6.1.7601]
opyright  2009 Microsoft Corporation. fill rights reserved.
:\Users\UserName>cd C:\Program FilesSUS EPfiSPhase 2 GEM
C:\Program FilesSUS EPfiSPhase 2 GEM>GEM.exe "C:\Users\UserName\Desktop\GEM P2 Sa
mple Input FilesSGEM_tractor_sample_inputs.csu" -c
:SProgram FilesSUS EPfiSPhase 2 GEMMJS Environmental Protection figency
GEM P2u3.0
rocessing "C:\UsersSUserNane\Desktop\GEM P2 Sample Input FilesSGEM_tractor_samp
e_inputs.csu"
rocessing Run ID Sample_1 	Complete?
rocessing Run ID Sample_2 	Complete?
rocessing Run ID Sample_3 	Complete?
rocessing Run ID Sample_4 	

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