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Transportation and Climate

Greenhouse Gas Emissions Model (GEM) for Medium- and Heavy-Duty Vehicle Compliance

NOTE: You will need Adobe Acrobat Reader, available as a free download, to view some of the files on this page. See EPA's PDF page to learn more about PDF, and for a link to the free Acrobat Reader.

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.

Phase 2 GEM Simulation Model (Supporting the Proposed Phase 2 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 proposed  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 proposed version of Phase 2 GEM intended for simulating vehicle compliance for model years 2021 and beyond. The report of the peer review on Phase 2 GEM includes the comments received on the model and EPA’s responses.  Last, the MATLAB/Simulink code that is recommended for powertrain testing according to 40 CFR 1037.550 is provided. 

GEM Simulation Model v2.0.1 (Supporting the Final Heavy-Duty Vehicle Greenhouse Gas Emissions and Fuel Efficiency Rules (“Phase 1”))

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 the GEM for simulating vehicle compliance. Lastly, the report of the peer review of GEM v1.0 includes the comments received on the model and EPA’s responses.

  • Read the user guide for model architecture, how to use the model, and inputs used to determine the final standards (PDF) (16 pp, 693K, EPA-420-B-11-019, August 2011)
  • Download the executable version of GEM_Setup.exe (zip) (194MB)
    • GEM v2.0.1 (zip) (189MB, May 2013): A revision has been made to GEM to accommodate the revision to 49 CFR 535.6(b)(3) which derives the fuel consumption FEL from the CO2 FEL value rounded to the nearest whole number. The update also includes the previous update to address an installation bug has been identified for computers using a Windows 7 operating system. Due to the security setup of the Windows 7 operating system, the GEM executable code will not run from the default installation folder of C:\Program Files(x86)\EPA\GEM or from any other folder under C:/Program Files. This bug can be avoided by clicking on Browse under "Choose Installation Location," and then selecting a different local folder into which to install the GEM.
    • Please unzip the file first and then follow the GEM User Guide instruction to install GEM v2.0.1
  • Peer Review Report and Response to Comments (PDF) (106 pp, 1.67MB, EPA-420-R-11-007, August 2011) This document contains the Peer Review Report, which is comprised of comments from four separate peer reviewers, and EPA’s response to those comments.

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