July 15, 2016

MEMORANDUM

SUBJECT:	"Greenhouse gas Emissions Model" (GEM) simulation tool, Version 3.0

FROM:	Houshun Zhang, OTAQ/ASD

TO:	Greenhouse Gas Emissions Standards and Fuel Efficiency Standards for Medium- and Heavy-Duty Engines and Vehicles - Phase 2 - EPA-HQ-OAR-2014-0827


The enclosed compact disk contains the open source code and executable program for Version 3.0 of the "Greenhouse gas Emissions Model" (GEM) simulation tool. This model was developed to support the Phase 2 greenhouse gas emission standards for heavy-duty highway vehicles in 40 CFR part 1037. The model was finalized on July 15, 2016.

EPA's Greenhouse Gas Emissions Model (GEM) is a free, desktop computer application that estimates the greenhouse gas emissions and fuel efficiency performance of specific aspects of heavy-duty vehicles.  GEM is the agencies' official software application for manufacturers to certify their trucks.  GEM is written in the "Matlab/Simulink" computer language.  During the process of this program's development, the agencies recognized that not all GEM users would possess the requisite commercial licenses to execute the GEM source code.  Consequently, the agencies developed an executable version of GEM that runs on a desktop or laptop computer without the Matlab/Simulink software licenses. The official GEM executable software program can be downloaded for free for unlimited use from EPA's website at http://www.epa.gov/otaq/climate/gem.htm.  

In addition to this downloadable executable version of GEM, the agency also maintains an open source version of GEM, which contains all of GEM's source code in the Matlab/Simulink programming language.  This source code is freely available upon request.  The source code is self-explanatory without a separate user manual because the agencies' computer programmers inserted explanatory remarks and comments within the source code itself.   While the GEM source code is available to the public for transparent inspection of the code, but it may not be used for official certification, compliance or enforcement purposes.  Therefore, the agencies do not provide technical support for executing the GEM source code.  It should also be noted that in order to execute the GEM source code, a user must have separate commercial licenses from MathWorks, Inc. for "Matlab", "Simulink", "Stateflow", and Matlab's "Statistics Toolbox" software.


Encl. "Greenhouse gas Emissions Model" (GEM) simulation tool, Version 3.0, compact disk
