Greenhouse Gas Emissions Model 

(GEM) User Guide 
Greenhouse Gas Emissions Model
 

(GEM) User Guide
 

Assessment and Standards Division 

Office of Transportation and Air Quality 

U.S. Environmental Protection Agency 

EPA-420-B-10-039 

October 2010 
 

 

 

 

 

 

 

 

 

 

 

 

Greenhouse gas Emissions Model (GEM) User Guide 

The Greenhouse gas Emissions Model was developed by EPA as a means for 

determining compliance with the proposed GHG emissions and fuel consumption vehicle 

standards for Class 7 and 8 combination tractors and Class 2b-8 vocational vehicles developed 

by EPA and NHTSA respectively. The model itself is part of the proposed rule. See Section 

II.B.2 of the preamble and Chapter 4 of the draft RIA. It is a free, desktop computer application. 

GEM is designed to operate on a single computer. The downloadable installation file 

located on the EPA website at http://www.epa.gov/otaq/climate/regulations.htm contains the 

application executable file and other supporting files, which will be described in this guide. 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 contact: 

Assessment and Standards (ASD) Hotline at: 

734-214-4636 or 

Email: ASDInfo@epa.gov 

This user guide contains the model documentation with details on the model’s input files, 

algorithms, and output files. It also includes instructions on how to use GEM. In addition, this 

document includes the input file which was used to determine the baseline and proposed 

greenhouse gas emissions and fuel efficiency standards for Class 7 and 8 tractors and Class 2b-8 

heavy-duty vehicles. Some of the information provided here are also contained in Chapter 4 of 

the draft RIA. 

1. GEM Documentation v1.0 

This section describes the GEM vehicle model architecture, the list of pre-defined input 

parameters, output calculations, and the installation and usage of the MATLAB/Simulink version 

of GEM. 

1.1. Vehicle Model Architecture 

Table 1 outlines the Class 2b-8 vehicle compliance model architecture, which is 

comprised of six systems: Ambient, Driver, Electric, Engine, Transmission, and Vehicle. With 

the exception of “Ambient” and “Driver,” each system consists of two to four component 

models. The function of each system and their respective component models, wherever 

applicable, is discussed in this section. 

1 
 

 

 

 

	 

	 

	 

	 

	 

	 

	 

	 

	 

Table 1: Vehicle Model Architecture 

System Component Models 

Ambient 

Driver 

Electric 

Engine 

Transmission 

Vehicle 

none 

none 

Starter; Electrical Energy System; Alternator; Accessory (electrical) 

Cylinder; Accessory (mechanical) 

Clutch; Gearbox 

Chassis; Final Drive 

•	 Ambient – This system defines ambient conditions such as pressure, temperature, and 

road gradient, where vehicle operations are simulated. 

•	 Driver – GEM is a forward-looking driving model. Rather than constantly matching the 

exact drive cycle, the driver model considers the current speed and the desired future 

speed to try to predict the necessary power required to close the gap and follow the 

driving trace. If the driver misses the target, a different power request is sent to the 

engine and/or brakes are applied. This search for the proper vehicle speed occurs at 

every simulation time step. The feedback loop uses a PID controller. 

•	 The “Electric” system consists of four components: Starter, Electrical Energy System, 

Alternator, and Electrical Accessory 

o	 Starter – This models the starter for the engine, which is identical for most 

vehicles. 

o	 Electrical Energy System – GEM simulates a standard 12 or 24 volt lead-acid 

battery, which provides currents to the starter and electrical systems for engine 

starting, lighting, and vehicle controls. This module estimates State-of-Charge 

(SOC), internal ohmic resistance and open circuit voltage, voltage and current of 

electrical energy storage system. 

o	 Alternator – This models the alternator that generates electricity for the battery 

and electrical system. The model calculates voltage and current of the AC 

alternator based on alternator performance maps and charge control strategy. 

o	 Electrical Accessory – All vehicles have a number of electrical loads, some of 

which are necessary to operate the vehicle. The engine control unit (ECU), fuel 

injectors and fuel pump for instance are electrical loads that are constantly on the 

battery, and these are already taken into account in the fuel map. 

•	 The “Engine” system consists of two components: Cylinder and Mechanical Accessory 

o	 Cylinder – The cylinder model is based on a fuel map and torque curves at wide 

open throttle (full load) and closed throttle (no load). The engine fuel map 

features three sets of data: engine speed, torque, and fueling rate at pre-specified 

engine speed and torque intervals. The fuel map was developed from 

experimental results adjusted to reflect projected future engine performance. It is 

not a physics-based model and does not attempt to model in-cylinder combustion 

process. The engine torque and speed are used to select a fuel rate based on the 

fuel map. This map is adjusted automatically by taking into account three 

different driving types: acceleration, braking, and coasting. The fuel map, torque 

curves, and the different driving types can be adjusted by the user, but there are a 

number of default engines pre-programmed into GEM. 

2 
 

 

 

 

 

 

 

 

 

 

	 

	 

	 

	 

	 

	 

	 

	 

o	 Mechanical Accessory – Most vehicles run a number of accessories that are 

driven via mechanical power from the engine. Some of these accessories are 

necessary for the vehicle to run, like the coolant pump, while others are only used 

occasionally and at the operator’s discretion such as the air conditioning 

compressor. Some heavy-duty vehicles also use Power Take Off (PTO) to 

operate auxiliary equipment, like booms, and these would also be modeled as a 

mechanical accessory. 

•	 The manual “Transmission” system consists of two components: a Clutch and a Gearbox 

o	 Clutch – This component model simulates the clutch for a manual transmission. 

o	 Gearbox – A simple gearbox model is used for a manual transmission, and the 

number of gears and gear ratios are predefined for compliance purposes. This 

component model consists of a map using gearbox speed and torque as inputs to 

model the efficiency of each gear. 

•	 The “Vehicle” system consists of two components: Chassis and Final Drive 

o	 Chassis – This portion models the shell of the vehicle including the tires. The 

drag coefficient, mass of the vehicle, frontal area and other parameters are housed 

in this component. For tire simulation, the user specifies the configuration of 

each axle on the vehicle, including the tire diameter and the rolling resistance. 

o	 Final Drive – The gear ratio for the differential is predefined for compliance 

purposes. The efficiency is defined by a map based on the transmission output 

speed and torque. 

1.2.	 List of Predefined Input Parameters for Class 7/8 Combination 

Tractor Models 

Although many technologies can potentially achieve GHG emission and fuel 

consumption reductions, EPA and NHTSA are of the initial view that for the rule’s proposed 

timeframe, some may be too complex to model (e.g., hybrid control) while others require 

standardization such as the calculation of GHG and fuel consumption benefits due to 

aerodynamic improvements which would require an input for the tractor frontal area. To better 

capture the GHG emission and fuel consumption benefits in the simulation model as well as to 

avoid unintended consequences in the real world, the agencies have identified a set of parameters 

that are consistent across various manufacturers for this rulemaking period and are proposing 

that these parameters be used as predefined inputs to the model. EPA and NHTSA are proposing 

to standardize the tractor frontal area, tractor-trailer total and payload weight, gear box and its 

efficiency, final drive ratio, engine/transmission/wheel inertia, accessory load, axle base, tire 

radius, trailer tire coefficient of rolling resistance (Crr, trailer tires), and engine fuel map. The 

agencies are proposing to use these standardized input parameters in the simulation model for all 

seven proposed subcategories of combination tractors. The predefined values, if finalized, then 

will remain in force unless and until EPA and NHTSA amend the rule to change the values. 

Table 2 lists the specific values of these parameters. 

3 
 

 

 

 

 

 

 


 

Table 2: Combination Tractor Modeling Input Parameters 

MODEL TYPE CLASS 8 CLASS 8 CLASS 8 CLASS 8 CLASS 8 CLASS 7 CLASS 7 

Regulatory 

Subcategory 

Sleeper Cab 

High Roof 

Sleeper Cab 

Mid Roof 

Sleeper Cab 

Low Roof 

Day Cab 

High Roof 

Day Cab 

Low/Mid Roof 

Day Cab 

High Roof 

Day Cab 

Low/Mid Roof 

Fuel Map 15L - 455 HP 11L - 350 HP 

Gearbox 10-speed 

Manual 

10-speed 

Manual 

10-speed 

Manual 

10-speed 

Manual 

10-speed 

Manual 

10-speed 

Manual 

10-speed 

Manual 

Gearbox Ratio 14.8, 10.95, 8.09, 5.97, 4.46, 3.32, 2.45, 1.81, 1.35, 1 

11.06, 8.19, 6.05, 4.46, 

3.34, 2.48, 1.83, 1.36, 1, 

0.75 

Gearbox 

Efficiency 0.96, 0.96, 0.96, 0.96, 0.98, 0.98, 0.98, 0.98, 0.98, 0.98 0.96, 0.96, 0.96, 0.96, 0.98, 

0.98, 0.98, 0.98, 0.98, 0.98 

Engine Inertia 

(kg-m2) 4.17 4.17 4.17 4.17 4.17 3.36 3.36 

Transmission 

Inertia (kg-m2) 0.2 0.2 0.2 0.2 0.2 0.2 0.2 

All Axle Inertia 

(kg-m2) 360 360 360 360 360 233.4 233.4 

Loaded Tire 

Radius (m) 0.489 0.489 0.489 0.489 0.489 0.489 0.489 

Body Mass (kg) 14742 13041 13154 14061 12474 11340 9752 

Cargo Mass (kg) 17236 17236 17236 17236 17236 11340 11340 

Total weight (kg) 31978 30277 30391 31298 29710 22680 21092 

Total weight (lbs) 70500 66750 67000 69000 65500 50000 46500 

Frontal Area (m2

) 9.8 7.7 6 9.8 6 9.8 6 

Coefficient of 

Aerodynamic 

Drag 

OEM Input OEM Input OEM Input OEM Input OEM Input OEM Input OEM Input 

Axle Base 5 5 5 5 5 4 4 

Electrical 

Accessory Power 

(W) 

360 360 360 360 360 360 360 

Mechanical 

Accessory Power 

(W) 

1000 1000 1000 1000 1000 1000 1000 

Final Drive Ratio 2.64 2.64 2.64 2.64 2.64 3.73 3.73 

Tire CRR 

(kg/metric ton) = 0.425 × Trailer CRR + 0.425 × Drive CRR + 0.15 × Steer CRR 

Trailer Tire CRR 

(kg/metric ton) 6 6 6 6 6 6 6 

Steer Tire CRR 

(kg/metric ton) OEM Input OEM Input OEM Input OEM Input OEM Input OEM Input OEM Input 

Drive Tire CRR 

(kg/metric ton) OEM Input OEM Input OEM Input OEM Input OEM Input OEM Input OEM Input 

Vehicle Speed 

Limiter (mph) OEM Input OEM Input OEM Input OEM Input OEM Input OEM Input OEM Input 

4
	
 

 

1.3.	 List of Predefined Input Parameters for Class 2b-8 Vocational 

Vehicle Models 

Likewise, EPA and NHTSA are proposing to standardize a set of parameters for the three 

proposed Class 2b-8 vocational vehicle types, which the agencies refer to as Vocational LightHeavy (VLH), Vocational Medium-Heavy (VMH), and Vocational Heavy-Heavy (VHH). These 

predefined parameters include the coefficient of aerodynamic drag, truck frontal area, truck total 

and payload weight, the gear box and its efficiency, final drive ratio, engine/transmission/wheel 

inertia, accessory load, axle base, tire radius, and the engine fuel map. The predefined values, if 

finalized, then will remain in force unless and until EPA and NHTSA amend the rule to change 

the values. The specific values of these parameters are listed in Table 3. 

5 
 

 

 

 

 

 

 

 

 

Table 3: Vocational Vehicle Modeling Input Parameters 

Model Type Heavy Heavy-Duty Medium Heavy-Duty Light Heavy-Duty 

Regulatory 

Subcategory 

Vocational Truck 

(Class 8) 

Vocational Truck 

(Class 6-7) 

Vocational Truck 

(Class 2b-5) 

Fuel Map 15L - 455 HP 7L - 270 HP 7L - 200 HP 

Gearbox 10-speed Manual 6-speed Manual 6-speed Manual 

Gearbox Ratio 14.8, 10.95, 8.09, 5.97, 4.46, 

3.32, 2.45, 1.81, 1.35, 1 

9.01, 5.27, 3.22, 

2.04, 1.36, 1 

9.01, 5.27, 3.22, 

2.04, 1.36, 1 

Gearbox Efficiency 0.96, 0.96, 0.96, 0.96, 0.98, 

0.98, 0.98, 0.98, 0.98, 0.98 

0.92, 0.92, 0.93, 

0.95, 0.95, 0.95 

0.92, 0.92, 0.93, 

0.95, 0.95, 0.95 

Engine Inertia (kg-m2

) 4.17 2.79 2.79 

Transmission Inertia 

(kg-m2) 0.2 0.1 0.1 

All Axle Inertia (kg-m2

) 200 60 60 

Loaded Tire Radius (m) 0.489 0.389 0.378 

Body Mass (kg) 13154 6328 4672 

Cargo Mass (kg) 17236 5080 2585 

Total weight (kg) 30391 11408 7257 

Total weight (lbs) 67000 25150 16000 

Frontal Area (m2

) 9.8 9 9 

Coefficient of 

Aerodynamic Drag 0.7 0.6 0.6 

Axle Base 3 2 2 

Electrical Accessory 

Power (W) 360 360 360 

Mechanical Accessory 

Power (W) 1000 1000 1000 

Final Drive Ratio 2.64 3.36 3.25 

Tire CRR 

(kg/ton) = 0.5 × Drive CRR + 0.5 × Steer CRR 

Trailer Tire CRR 

(kg/metric ton) Not applicable Not applicable Not applicable 

Steer Tire CRR 

(kg/metric ton) OEM Input OEM Input OEM Input 

Drive Tire CRR 

(kg/metric ton) OEM Input OEM Input OEM Input 

1.4. Output Processes 

The outputs produced by GEM include post processes to calculate the final weighted results. 

6 
 

 

 

 

 

 

 

 

 

 

 

 

 

	 

	 

	 

	 

	 

GEM produces a cycle-weighted gram CO2/ton-mile and gallon/1000 ton-mile result which 

incorporates the proposed drive cycle weightings of the ARB transient cycle, 55 mph steady state 

cruise, and 65 mph steady state cruise cycle, as shown in Table 4. 

Table 4: Drive Cycle Weighting 

CATEGORY 

CLASS 8 

SLEEPER CAB 

TRACTORS 

CLASS 7/8 

DAY CAB 

TRACTORS 

CLASS 2b-8 

VOCATIONAL 

VEHICLES 

ARB Transient 5% 19% 42% 

55 mph Cruise 9% 17% 21% 

65 mph Cruise 86% 64% 37% 

GEM converts the mile per gallon result into ton-mile space by using the proposed 

payload for each regulatory class – 19 tons for Class 8 tractors, 12.5 tons for Class 7 tractors, 19 

tons for HHD vocational vehicles, 5.6 tons for MHD vocational vehicles, and 2.85 tons for LHD 

vocation vehicles. 

GEM calculates the gallons/1000 ton-mile weighted result by converting the weighted grams 

CO2/ton-mile result. The gram CO2/ton-mile result is multiplied by 1000 and divided by 10,180 

grams CO2 per gallon of diesel fuel. 

2. Instructions on How to Install and Use GEM 

The executable form of GEM can be downloaded from the website. Please follow the 

procedure below to run the executable version. 

1.		 Unzip the file (GEM Setup.zip), and run the executable "GEM_Run.exe". 

2.		 If the executable file runs and launches a Graphical User Interface (GUI) as shown in 

Figure 1, then your computer system is ready to run the model. 

3.		 If you receive the error message "application configuration is incorrect," then run 

"setup.bat". The error message is related to missing system Visual Studio Redistributable 

dll files and "setup.bat" will automatically run the Microsoft vcredist_x86.exe on the 

client systems experiencing this issue. 

4.		 Now, rerun the executable file "GEM_Run.exe". You should be able to see the GUI as 

shown in Figure 1. 

5.		 The simulation output is created in a folder "C:\GEM_Results\Month_Day_Year-Time". 

The output file in XML format can be opened with Excel to see the results. Each 

simulation creates a different folder using the above naming format. 

The GEM input screen, as shown in Figure 1, provides the user the ability to enter the 

required parameters into the model. There are essentially two types of parameters – ones 

required for information and ones which impact the model. The first set of parameters which are 

required to provide information to EPA and NHTSA and where GEM copies the information 

from the input screen to the output screen. These include the following: 

7 
 

 

 

 

 

 

 

 

	 

	 

	 

	 

	 

	 

	 

	 

	 

	 

	 

	 

	 

	 

	 

	 

	 

•	 Manufacturer Name 

•	 Email Address 

•	 Date 

•	 VERIFY User ID 

•	 VERIFY ID 

•	 Vehicle Family 

•	 Vehicle Subfamily 

•	 Engine Family 

•	 Engine Subfamily 

•	 Engine Model Year 

The second set of parameters affects how GEM calculates the final result. The list below 

describes each input and how it is used within GEM. 

•	 Vehicle Model Year: The pull-down allows the user to select either Pre 2014 MY, 

2014-2016 MY, or Post 2017 MY. The Vehicle Model Year selects the appropriate 

fuel map in the model. The Pre 2014 MY allows users to evaluate the baseline 

heavy-duty vehicle’s engine fuel map. The 2014-2016 MY selection uses the engine 

fuel maps which meet the proposed 2014 MY engine standards. The Post 2017 MY 

option uses engine fuel maps which meet the 2017 MY proposed engine standards. 

•	 Regulatory Class: The user must select one of the designated regulatory 

subcategories. The selection leads the model to use the appropriate predefined inputs 

and post processing parameters, as outlined in Sections 1.2, 1.3, and 1.4 of this 

Guidance. 

•	 Coefficient of Drag: The Cd value is input by the user based on the proposed 

aerodynamic bins, as discussed in both the preamble and draft RIA. This input is 

only required for combination tractors. No input is required for vocational trucks. 

•	 Steer Tire Rolling Resistance: The coefficient of rolling resistance for the steer tires 

should be input by the user in terms of kg/metric ton. Please note that the units are in 

kg/metric ton where the typical value is greater than 5.5 kg/metric ton. The units are 

not in kg/kg or lb/lb (the other industry norm) where the values are typically greater 

than 0.0055 kg/kg or lb/lb. 

•	 Drive Tire Rolling Resistance: The coefficient of rolling resistance for the drive tires 

should be input by the user in terms of kg/metric ton. Please note that the units are in 

kg/metric ton where the typical value is greater than 5.5 kg/metric ton. The units are 

not in kg/kg or lb/lb (the other industry norm) where the values are typically greater 

than 0.0055 kg/kg or lb/lb. 

•	 Vehicle Speed Limiter: If the vehicle contains a vehicle speed limiter, then the setting 

corresponding to the nearest whole mile per hour should be selected. GEM will limit 

the maximum speed of the vehicle to the value selected. This input is only available 

for combination tractors. No input is allowed for vocational trucks. 

•	 Vehicle Weight Reduction: If a combination tractor contains lighter weight wheels or 

tires, as described in the preamble, draft RIA, and regulations, then the user would 

input the sum of the weight reductions prescribed by the weight bins. This input is 

only available for combination tractors. No input is allowed for vocational trucks. 

8 
 

 

 

 

 

 

•	 Extended Idle Reduction: If a sleeper cab combination tractor contains an extended 

idle reduction technology and a 5 minute automatic engine shut-off, then the user 

would select the 5 g/ton-mile reduction. If not, then 0 should be selected. This input 

is only available for sleeper cab combination tractors. No input is allowed for day 

cab combination tractors or vocational vehicles. 

Figure 1 – GEM Input Screen 

After the user selects “RUN,” GEM will conduct the simulation of each of the drive 

cycles. The output will provide both the gram CO2/ton-mile and gallon/1000 ton-mile result in 

the .xml file, as shown in Figure 2. The simulation output is created in a folder 

"C:\GEM_Results\Month_Day_Year-Time." The output file is in xml format and can be opened 

with Excel. Each simulation creates a different folder using the “Month_Day_Year-Time” 

naming format. 

9 
 

 

 

 

 

 

 

 


 

Figure 2 – Sample GEM Output .xml File 

3. MATLAB/Simulink Version of GEM
 

In addition to providing executable file which the agencies have proposed to be used for 

certification purposes, the agencies are also furnishing a MATLAB/Simulink version of GEM to 

allow stakeholders to review the model architecture in detail. The system requirements for GEM 

include a minimum RAM of 1 GB, MATLAB, Simulink and Stateflow (version 2009b or later), 

and approximately 250 MB of disk storage.1,2,3 No separate license is required to run the 

program other than for MATLAB, Simulink, and Stateflow. Although the source code is 

available to users, all of the component initialization files, control strategies and the underlying 

MATLAB/Simulink/Stateflow-based models should remain fixed and should not be manipulated 

by the users when assessing their compliance. For these reasons, the stand-alone executable 

model independent of MATLAB/Simulink/Stateflow licenses has been created. The agencies 

recommend using the executable file for the evaluation of various truck configurations, as it was 

developed for the end user. 

3.1 Installation Instructions for the MATLAB/Simulink Version 

Copy the entire directory from the web link into the user’s hard drive, then follow the 

procedures below. 

1 http://www.mathworks.com/products/matlab © 1994-2010 The MathWorks, Inc. 2 http://www.mathworks.com/products/simulink © 1994-2010 The MathWorks, Inc. 

3 http://www.mathworks.com/products/stateflow © 1994-2010 The MathWorks, Inc. 

10 
 

 

	 

	 

	 

	 

	 


 


 


 


 


 


 


 


 


 


 


 

1.		 Start the MATLAB and change the current directory to the location where the tool is 

unzipped and saved. 

2.		 Run the MATLAB script "Run_GEM_sim.m" to launch the GUI window to start using 

the tool. 

3.		 Select one radial button on the left-hand side of the window to choose an appropriate 

truck subcategory. 

4.		 Enter proper values for "Coefficient of Aerodynamic Drag," "Steer Tire Rolling 

Resistance," and "Drive Tire Rolling Resistance" on the right-hand side of the window 

(see Section 2 above which describes each input). 

5.		 Click the "RUN" button. Then, the tool will simulate the three different driving cycles 

(ARB transient, 55 mph, and 65 mph) and display the final results in the Matlab 

Command Window. The tool will also display plots of vehicle speed for all three cycles. 

3.2 Input File Structures 

The programs that are downloaded from website consist of the following files in the main 

directory: 

Run_GEM_sim.m: a Matlab file used to launch the simulation
	

GEM_manual_v1.mdl: Simulink file containing vehicle and all submodels
	

run_preproc.m
	

run_postproc.m
	

GEM_sim.m
	

run_55mph.m
	

run_65mph.m
	

run_transient.m
	

drive_cycles folder
	

executable folder
	

param_files folder
	

4. Input Files Used to Calculate the Proposed GHG Emissions and Fuel 

Efficiency Standards 

The agencies developed the baseline and proposed standards using the input tables included 

in Table 5 and Table 6. 

11 
 


 

Table 5: Input Parameters for Proposed Tractor Standards 

CLASS CLASS 8 CLASS 8 CLASS 8 CLASS 8 CLASS 8 CLASS 7 CLASS 7 

Regulatory 

Subcategory 

Sleeper Cab 

High Roof 

Sleeper Cab 

Mid Roof 

Sleeper Cab 

Low Roof 

Day Cab 

High Roof 

Day Cab 

Low/Mid Roof 

Day Cab 

High Roof 

Day Cab 

Low/Mid Roof 

Baseline 

Fuel Map 2010 MY 2010 MY 2010 MY 2010 MY 2010 MY 2010 MY 2010 MY 

Cd 0.69 0.76 0.81 0.69 0.81 0.69 0.81 

Steer Tire CRR 7.8 7.8 7.8 7.8 7.8 7.8 7.8 

Drive Tire CRR 8.2 8.2 8.2 8.2 8.2 8.2 8.2 

Weight Reduction 

(lbs) 0 0 0 0 0 0 0 

Extended Idle None None None N/A N/A N/A N/A 

2014 MY Proposed Standard 

Fuel Map 2014 MY 2014 MY 2014 MY 2014 MY 2014 MY 2014 MY 2014 MY 

Cd 0.60 0.72 0.76 0.62 0.77 0.62 0.77 

Steer Tire CRR 6.54 6.87 6.87 6.87 6.99 6.87 6.99 

Drive Tire CRR 6.92 7.26 7.26 7.26 7.38 7.26 7.38 

Weight Reduction 

(lbs) 400 400 400 400 400 400 400 

Extended Idle Yes Yes Yes N/A N/A N/A N/A 

2017 MY Proposed Standard 

Fuel Map 2017 MY 2017 MY 2017 MY 2017 MY 2017 MY 2017 MY 2017 MY 

Cd 0.60 0.72 0.76 0.62 0.77 0.62 0.77 

Steer Tire CRR 6.54 6.87 6.87 6.87 6.99 6.87 6.99 

Drive Tire CRR 6.92 7.26 7.26 7.26 7.38 7.26 7.38 

Weight Reduction 

(lbs) 400 400 400 400 400 400 400 

Extended Idle Yes Yes Yes N/A N/A N/A N/A 

12
	
Table 6: Input Parameters for Proposed Vocational Vehicle Standards 

Model Type Heavy Heavy-Duty Medium Heavy-Duty Light Heavy-Duty 

Regulatory Subcategory Vocation Truck 

(Class 8) 

Vocation Truck 

(Class 6-7) 

Vocation Truck 

(Class 2b-5) 

Baseline 

Fuel Map 2010 MY 2010 MY 2010 MY 

Tire CRR (kg/metric ton) 9.0 9.0 9.0 

2014 MY Proposed Standard 

Fuel Map 2014 MY 2014 MY 2014 MY 

Tire CRR (kg/metric ton) 8.1 8.1 8.1 

2017 MY Proposed Standard 

Fuel Map 2017 MY 2017 MY 2017 MY 

Tire CRR (kg/metric ton) 8.1 8.1 8.1 

13