9.1. Clean Truck Check#
Clean Truck Check (CTC)–Heavy-Duty Inspection and Maintenance (HD I/M) Program–was approved by the California Office of Administrative Law (OAL) on October 5, 2022, and implementation began on January 1, 2023. CTC applies to all on-road, non-gasoline heavy-duty vehicles with a gross vehicle weight rating over 14,000 pounds that operate in California. This includes vehicles registered out of state and out of the country. CTC requires vehicle owners to demonstrate that their emissions control systems are properly functioning, thereby reducing excess NOx and PM emissions resulting from poor maintenance and tampering. The emission benefits from CTC in EMFAC2025 reflect lower rates of emissions-related deterioration due to induced repairs and better maintenance. The regulation requires on-board diagnostics (OBD)-equipped vehicles to submit their OBD data periodically. Non-OBD-equipped vehicles are required to submit their opacity test periodically, and any non-compliant vehicles will receive a DMV registration hold. The program is scheduled to be implemented in four phases:
Phase 1: Starting January 2023, high-emitter vehicles were screened with portable emissions acquisition systems (PEAQS) in the South Coast and San Joaquin Valley regions.
Phase 2: Enforcement of compliance certification requirements began in mid-2023; the California Department of Motor Vehicles (DMV) began holding vehicle registrations of non-compliant California-registered vehicles.
Phase 3: Starting in 2025, periodic testing is now enforced, and heavy-duty vehicles are required to have two tests per year.
Phase 4: Starting in 2028, OBD-equipped vehicles will be required to submit their tests four times per year.
Staff developed a model to incorporate the program’s different phases to calculate the emission benefit, which is described further in Appendix D of the CTC ISOR (CARB, 2021). At a high level, EMFAC2025 uses outputs from a MIL-On solver. This unit solves a series of ordinary differential equations that describe the evolution of the fraction of vehicles with their MIL lamp on, based on:
Initial fractions at the start of the program (which depend on the EMFAC vehicle category and model year).
Program phase, which provides inputs such as expected repair rates and test frequency.
The output of the unit is MIL ON fractions by calendar year, EMFAC vehicle category, vehicle model year, and air basin.
To reflect the emissions benefits of CTC in EMFAC2025, the baseline NOx and PM deterioration rates for applicable vehicle categories and fuel types are adjusted using the ratio of the new MIL ON fraction (after the regulation is in place) to the old MIL ON fraction (before the regulation is in place).