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On August 15, 2019, the U.S. Environmental Protection Agency (EPA) published to the Federal Register its official approval of EMFAC2017 as the latest update to the California EMFAC (short for EMission FACtor) model, as submitted by the California Air Resources Board (CARB) on July 20, 2018. EMFAC is a computer model used for estimating emission rates for on-road mobile sources in California for calendar years 2000 to 2050. This update is based on new and improved data and is approved for use in state implementation plan (SIP) development and transportation conformity in California for calculating emissions from on-road mobile sources (i.e. passenger cars, trucks, motorcycles, motor homes, and buses). EMFAC2017 is considered a major update to EMFAC because it includes new data and significant changes to the methodologies for calculating on-road mobile source emissions.

However, on September 27, 2019, the EPA and the National Highway Traffic Safety Administration (NHTSA) published the first part of a two-part rule titled “Safer Affordable Fuel Efficient (SAFE) Vehicles Rule Part One: One National Program” (Rule), which became effective on November 26, 2019. The Rule revoked California's authority to establish its own greenhouse gas (GHG) emissions standards and set zero-emission vehicle (ZEV) mandates in the state. California's GHG standards and ZEV sales are critical components to the state's ability to offset tailpipe emissions toward the goal of reaching air quality attainment standards and meeting climate needs.

Therefore, the approval of the Rule means that the previously approved EMFAC2017 model no longer accurately estimates future transportation emissions and requires off-model adjustment factors until the next update in order to reflect the impacts of the Rule. Note that the Rule impacts emissions only from gasoline-powered Light Duty Vehicles (i.e. LDA, LDT1, LDT2, and MDV vehicle categories).

CARB has provided off-model adjustment factors for EMFAC2017 to account for the impacts of the Rule. These adjustment factors are multipliers that can be applied to EMFAC emissions outputs and are available via CARB's website. Because these adjustments will multiply on-road mobile source emissions to varying extents (depending on year and pollutant) but always by a factor greater than 1, it can be expected that resulting emissions will increase, thus causing an increase in any potential fees related to mobile source emissions.

Process to apply EMFAC Off-Model Adjustment Factors

Part Two of the SAFE Vehicle Rule will result in additional impacts, the full extent of which will not be known until it is released. Trinity Consultants will follow the progress of Part Two's development, approval, and implications. Additional information on CARB's EMFAC off-model adjustment factors can be found on their website.