California Department of Transportation

Last Updated: Wednesday, March 30, 2016 2:06 PM


Emission factors that represent the vehicle fleet, speeds, and environmental conditions associated with a project are needed to perform project-level air quality modeling.The EMFAC model issued by the California Air Resources Board is used for this process in California. For more details regarding project-level "hot spot" modeling, please refer to the CO Protocol, Appendix B and the U.S. EPA's latest guidance Exit Caltrans website for particulate matter hot spot analysis.

EMFAC 2011 Exit Caltrans website was released by ARB on September 30, 2011. It was made available for conformity use by U.S. EPA on March 6, 2013 (Federal Register notice (PDF) Exit Caltrans website). All new air quality analysis must use EMFAC 2011 as of September 6, 2013. NEPA and CEQA (non-conformity-related) air quality analysis started since September 2011 should be using EMFAC 2011 for new studies, regardless of the version used for conformity.

Do not use EMFAC 2007 for new studies. Conformity studies begun with EMFAC 2007 may be completed with it as long as, in general, studies are completed within 3 years of starting work. For project-level conformity purposes, EPA will generally accept a project-level conformity determination if the Final NEPA document is completed and the project approved within 3 years of circulating the Draft NEPA document based on the older model version.

EMFAC software should be obtained from the ARB web Exit Caltrans website.

The EMFAC model and all supporting data are provided and supported by the California Air Resources Board Exit Caltrans website.


Caltrans and UC Davis interpreted the EMFAC model to provide a simplified user interface for project-level emission analysis, including emission factors and emission burden of criteria pollutants typically analyzed and Mobile Source Air Toxics (based on ARB's speciation factors for Total Organic Gases - TOG). For more information and to download the software package, see the CT-EMFAC page.

DO NOT USE CT-EMFAC 4 (EMFAC 2007) FOR ENVIRONMENTAL DOCUMENT AIR QUALITY STUDIES STARTED ON OR AFTER OCTOBER 1, 2011. Do not use CT-EMFAC 4 (EMFAC 2007) for ANY air quality studies (including conformity) started after September 5, 2013.

FOR CONFORMITY ANALYSIS: use EMFAC 2011-SG and -PL as documented in the latest EPA quantitative hot spot analysis guidance pending availability of CT-EMFAC 5 for that purpose. CT-EMFAC 5, if and when approved by EPA, will be an alternative model for conformity use.


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