Sunset Estimation for Biodiesel On-Road In-Use Requirements
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The sunset of the biodiesel on-road in-use requirements occurred on December 31, 2025. For more information, please view the Executive Order.
The purpose of this document is to provide user-friendly public guidance on how the California Air Resources Board (CARB) will estimate the penetration of new technology diesel engines (NTDE) in the California heavy-duty on-road diesel vehicle fleet under CARB’s Regulation on the Commercialization of Alternative Diesel Fuels (ADF regulation).12
Under the ADF regulation for the on-road sector,3 biodiesel in-use requirements necessitate the mitigation of NOx emissions associated with the use of biodiesel blends above the NOx control level. Biodiesel in-use requirements will sunset when the vehicle miles traveled (VMT) by heavy-duty on-road new technology diesel engines (NTDE) in California reaches 90 percent of the total VMT by the California heavy-duty on-road diesel vehicle fleet.
CARB will issue an Executive Order certifying that biodiesel in-use requirements are no longer in effect for the on-road sector once the threshold above has been reached.4
The ADF regulation requires that “The portion of VMT by on-road diesel vehicles in California represented by NTDEs will be determined using the most current CARB mobile source emissions inventory and any related tools.”5
CARB will determine the sunset dates for biodiesel in-use requirements using the current version of CARB’s online emissions inventory tool for on-road mobile sources (EMFAC),6 available here: https://arb.ca.gov/emfac/emissions-inventory. On-road emissions inventory data relevant to estimating the portion of VMT by on-road diesel vehicles in California represented by NTDEs can be downloaded by selecting the options shown below for EMFAC 2021:
| Inventory Option | EMFAC 2021 User Selection |
|---|---|
| Output | Onroad Emissions |
| Model Version | EMFAC 2021 v1.0.2 |
| Region Type | Statewide |
| Region | [Not applicable – autofilled to Statewide] |
| Calendar Year | [Select years of interest] |
| Season | Annual |
| Vehicle Category | EMFAC202x Categories |
| [Include all vehicle categories except LDA, LDT1, LDT2, MDV, MCY] | |
| Model Year | Select |
| [Include all available model years] | |
| Speed | Aggregate |
| Fuel | Diesel |
| Output Unit | tons/year |
After downloading the on-road emissions inventory data for the calendar years of interest, the percent of VMT by heavy-duty on-road NTDEs in California can be estimated for a given calendar year by:
Filtering the “Model Year” column and labeling model years 2011 and newer as NTDE and labeling model years 2010 and older as non-NTDE. CARB assumes that model year 2011 and newer vehicles, which contain model year 2010 and newer engines, are equipped with NTDEs for all heavy-duty on-road vehicle categories.
Summing cVMT (EMFAC 2021) or cVMT7 (EMFAC 2025) by heavy-duty on-road NTDEs across all heavy-duty on-road vehicle categories for each calendar year of interest.
Summing cVMT (EMFAC 2021) or cVMT (EMFAC 2025) by heavy-duty on-road vehicles across all heavy-duty on-road vehicle categories for each calendar year of interest.
Dividing the sum of cVMT (EMFAC 2021) or cVMT (EMFAC 2025) by heavy-duty on-road NTDEs for the given calendar year by the sum of cVMT (EMFAC 2021) or cVMT (EMFAC 2025) by the heavy-duty on-road diesel vehicle fleet for the same given calendar year.
- 1CARB’s ADF Regulation can be found in Title 13, California Code of Regulations, Sections 2293-2293.9 and Appendix 1 of Subarticle 2. Please note that all ADF regulation citations below are to Title 13, California Code of Regulations.
- 2Unlike the regulation itself, this document does not have the force of law. It is not intended to and cannot establish new mandatory requirements beyond those that are already in the ADF Regulation, nor can it supplant, replace or amend any of the legal requirements of the regulation. Conversely, any omission or truncation of regulatory requirements does not relieve entities of their legal obligation to fully comply with all requirements of the regulation.
- 3See ADF regulation subsection 2293.6(a)(4)(A).
- 4See ADF regulation subsections 2293.6(a)(4)(B).
- 5See ADF regulation subsection 2293.6(a)(4)(A).
- 6As of July 1, 2025, the most current version of CARB’s on-road mobile source emissions inventory is EMFAC 2025, and the most current US EPA-approved version of CARB’s on-road mobile sources emissions inventory is EMFAC 2021. US EPA approval is required for new versions of EMFAC for statewide use in State Implementation Plan (SIP) development and emissions analyses for conformity purposes. CARB plans to submit EMFAC 2025 for US EPA review in Spring 2026. CARB staff developed this guidance for use with EMFAC 2021 and EMFAC 2025.
- 7EMFAC 2021 and 2025 provide VMT data as conventional VMT (cVMT), which represents VMT from vehicles fueled by conventional fuels (e.g., diesel, gasoline, natural gas), electric VMT (eVMT), which represents VMT from vehicles powered by electricity, and Total VMT, which is the sum of cVMT and eVMT. The use of EMFAC 2025 to estimate of the portion of VMT by on-road diesel vehicles in California represented by NTDEs relies on cVMT.