Section 176(c) of the federal Clean Air Act establishes transportation conformity requirements that are intended to ensure that transportation activities do not interfere with air quality progress. Transportation conformity links and coordinates transportation and air quality planning processes through motor vehicle emissions budgets (Budgets) that are established in State Implementation Plans. Once Budgets are established in a State Implementation Plan and approved or determined adequate by U.S. EPA, subsequent transportation plans and programs produced by transportation planning agencies must demonstrate that the emissions from the plan or project do not exceed those budgets and thus “conform” to the State Implementation Plan.
For the San Joaquin Valley (Valley), U.S. EPA approved budgets for the 75 parts per billion 8-hour ozone standard that included budgets developed using the EMFAC2017 model. In 2021, California released a new version of its transportation model, EMFAC2021, which included reductions from new and revised regulations, such as the Advanced Clean Truck regulation and the Heavy Duty Omnibus regulation. Due to the updated data and methodologies, EMFAC2021 estimates higher overall emissions from the on-road vehicle population. Because of the increased emissions in the model, the Metropolitan Planning Organizations in the Valley may not be able to demonstrate transportation conformity against Budgets established using EMFAC2017. To align the Budgets with EMFAC2021, on March 27, 2025, CARB revised the Budgets in the Valley 75 ppb ozone plan.
Following the March 2025 update to the Budgets, the federal government took several actions affecting the emissions reductions accounted for in the Budgets. In June of 2025, the current federal administration adopted illegal congressional resolutions that purported to revoke California’s clean air waivers, including those needed to enforce regulations accounted for in EMFAC2021, the Advanced Clean Truck and the Heavy-Duty Vehicle Omnibus regulations.
In response to these federal actions and to ensure that transportation plans and programs produced by Metropolitan Planning Organizations in the Valley can meet the Clean Air Act requirement for transportation conformity, CARB is proposing to further update the Budgets for the Valley 75 ppb ozone plan. The current updates to the Budgets include the removal of the benefits from the Advanced Clean Truck and Heavy-Duty Omnibus regulations and an adjustment to align with EMFAC2021.
