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California Mobile Source Services

Yorke Engineering provides comprehensive compliance, reporting, and strategic planning support for California mobile source regulations overseen by the California Air Resources Board (CARB) and local air districts. We assist organizations affected by rules governing on‑road fleets, off‑road diesel equipment, forklifts, ports, warehouses, and public agencies. Our team helps clients understand regulatory applicability, maintain compliance, and plan for zero‑emission transitions.

Yorke Engineering has assisted over 100 fleets in navigating California mobile source regulations that impact their operations. Our services include determining which regulations apply to the fleet, evaluating current compliance with each applicable regulation, developing long-term compliance strategies, and assisting with reporting in the Diesel Off-Road Online Reporting System (DOORS); the Truck Regulations, Upload, and Compliance Reporting System (TRUCRS) for on-road diesel vehicles; and the South Coast Air Quality Management District’s (SCAQMD’s) Program Online Portal (POP).

On-Road Heavy-Duty Vehicles and Fleets

Diesel vehicles with a gross vehicle weight rating (GVWR) greater than 14,000 pounds have distinct fleet requirements in California, particularly as regulated by CARB. Yorke Engineering has assisted fleets of varying sizes, ranging from small fleets with fewer than three vehicles to large fleets with over 1,000 vehicles. A few of the typical tasks we commonly perform are shown below as examples:

• Compliance assessments and long-term compliance planning for companies subject to the Truck and Bus Regulation;
• TRUCRS reporting assistance to demonstrate compliance with the flexibility options of the Truck and Bus Regulation, including low-use, emergency use, nitrogen oxide (NO_X)-exempt area operations, heavy-crane, low-mileage work truck, phase-in, and agricultural provisions and exemptions;
• Compliance support for the CARB Fleet Rule for Public Agencies and Utilities (PAU);
• Compliance support for the SCAQMD Public Fleet Rules (such as Rule 1186.1, 1191, and 1196);
• Assisting with smoke test requirements, including the transition from the Periodic Smoke Inspection Program (PSIP) to the “Clean Truck Check” Program, also known as the Heavy-Duty Inspection and Maintenance (HD I&M) Program;
• Assistance with overlapping on-road regulatory requirements, such as smoke test requirements, fleet compliance with historic regulations, and evaluating applicability of the Advanced Clean Fleets (ACF) Regulation, as well as supporting compliance planning for State and Local Government (SLG) fleets, where applicable (see ACF section below);
• Funding assistance, such as Hybrid and Zero-Emission Truck and Bus Voucher Incentive Project) (HVIP) (see Funding section below);
• Assisting with CARB fleet audits; and
• Assisting with notices of non-compliance, such as Department of Motor Vehicles (DMV) renewal holds.

Off-Road Diesel Fleets

In total, our clients operate well over 250,000 horsepower (hp) of off-road diesel equipment, which is subject to the In-Use Off-Road Diesel-Fueled Fleets Regulation (ORD Regulation). Some facilities operate just a few pieces of equipment, while others operate more than 50. No matter the fleet size, Yorke Engineering can help bridge the gap between CARB compliance requirements and a facility’s equipment maintenance management strategies. A few of the typical tasks we commonly perform are shown below as examples:

• Fleet average and Best Available Control Technology (BACT) compliance calculations;
• Long‑term compliance planning aligned with current and future CARB off‑road diesel requirements;
• DOORS reporting assistance;
• Low-use tracking and strategies;
• Flex engine reporting;
• Agricultural provisions and exemptions;
• Cargo handling equipment compliance assistance for operations at a port or intermodal railyard;
• Funding assistance, such as California Clean Off-Road Equipment (CORE) (see Funding section below); and
• Compliance support for the Off‑Road Regulation amendments adopted in November 2022, including Tier phase‑out requirements, R99/R100 renewable diesel provisions, and ongoing fleet turnover planning.

Large Spark-Ignition (LSI)

Yorke Engineering has assessed over 500 pieces of LSI equipment and found exemptions for about 15% of them. Yorke Engineering has reported more than 350 LSI forklifts into DOORS for the initial reporting requirement that began on June 30, 2017. A few of the typical tasks we commonly perform are shown below as examples:

• Fleet assessments and compliance strategizing;
• Fleet average calculations;
• Low-use tracking and strategies;
• DOORS reporting assistance;
• Agricultural provisions and exemptions; and
• Coordination of LSI compliance requirements with the adopted Zero‑Emission Forklift (ZEF) Regulation (see ZEF section below).

Zero-Emission Forklifts (ZEF)

CARB adopted the ZEF Regulation to reduce emissions from LSI forklifts operating in California facilities, including warehouses, distribution centers, manufacturing sites, and ports. While CARB has delayed enforcement for privately owned fleets pending authorization from Region IX of the United States Environmental Protection Agency (U.S. EPA) under Clean Air Act §209(e), the regulation is in effect, and CARB is encouraging voluntary reporting and early compliance planning. SLG fleets are subject to the ZEF Regulation, and private fleets are advised to prepare for future enforcement.

Yorke Engineering provides comprehensive ZEF compliance and transition support, including:

• Forklift fleet inventories and applicability determinations under the ZEF Regulation;
• Evaluation of exemptions, extensions, and low‑use designations;
• Phase‑out and replacement planning based on forklift class, model year, and usage;
• Infrastructure readiness assessments, including charging and electrical capacity considerations;
• DOORS reporting assistance and voluntary reporting support;
• Coordination of ZEF compliance with existing LSI, off‑road diesel, and facility‑wide mobile source requirements; and
• Identification and pursuit of available funding and incentive programs to support ZEF transitions.

Funding

Since 2018 and the advent of Assembly Bill (AB) 617, there has been a significant push for funding cleaner mobile sources. Yorke Engineering can help clients navigate funding programs to find opportunities that suit each facility’s operational needs, as well as assist with the application process. Some of the most common funding programs include:

• HVIP;
• CORE Voucher Incentive Program;
• Carl Moyer Program Funding for Vehicle Replacement or Engine Repower (statewide funding with project types and timelines that vary by air district);
• Carl Moyer Program Funding for Zero-Emission Infrastructure;
• EnergIIZE for ZE Infrastructure;
• Funding Agricultural Replacement Measures for Emission Reductions (FARMER) Program;
• Surplus Off-Road Opt-In for NO_X (SOON) Funding Assistance for very large fleets (over 5,000 hp) operating in the South Coast Air Basin;
• Proposition 1B Goods Movement (legacy funding programs, where applicable); and
• Volkswagen (VW) Mitigation Funds, available statewide in a variety of categories, such as ZEV replacement, zero-emission infrastructure, zero-emission forklifts, etc.

Advanced Clean Fleets (ACF)

CARB adopted the ACF Regulation on April 28, 2023, with the regulation becoming effective October 1, 2023. ACF was designed to complement CARB’s Advanced Clean Truck (ACT) Regulation (established in 2021), which requires manufacturers selling trucks in California to meet annual ZEV or Near-Zero-Emission Vehicle (NZEV) sales goals starting in 2024.

ACF originally established fleet purchase and turnover requirements for certain owners and operators of medium‑ and heavy‑duty vehicles operating in California, with initial reporting and compliance obligations beginning in 2024. However, significant changes occurred in 2025 after CARB withdrew its request for a federal Clean Air Act waiver. As a result, CARB repealed its authority to enforce ACF purchase requirements on private high‑priority fleets and federal fleets, as well as the drayage truck fleet provisions.

As of 2026, the ACF Regulation remains in effect primarily for SLG fleets, which CARB can regulate without a federal waiver. These fleets are required to increase the use of zero‑emission vehicles as vehicles are replaced, subject to expanded exemptions, infrastructure‑delay provisions, and additional flexibility authorized by subsequent amendments and State legislation. CARB has also delayed certain 100% ZEV purchase requirements for affected public fleets.

Yorke Engineering continues to support clients navigating the evolving ACF landscape by providing targeted compliance and planning services aligned with current regulatory applicability. These services include:

• Applicability evaluations;
• Fleet and asset assessments;
• Reporting support;
• Exemption and extension strategy development; and
• Long-term ZEV transition planning for public-sector fleets.

To learn more about this suite of regulations, visit CARB’s website for the ACF program.

Additional Mobile Source Regulations and Projects

Yorke Engineering has experience with a wide variety of fleets in both the public and private sectors. Listed below are a few examples of programs we also support.

• SCAQMD Indirect Source Rules (ISRs) for Facility-Based Mobile Source Measures (FBMSMs), including Warehouse Rule 2305 (WAIRE Program);
• Transport Refrigerated Unit (TRU) Regulation;
• Cargo Handling Equipment (CHE) Regulation;
• Commercial Harbor Craft Regulation;
• Ocean Going Vessel (OGV) At Berth Regulation;
• Locomotive Regulation;
• Port-related studies and support;
• EMFAC and OFFROAD modeling; and
• Emission Inventory Reporting (EIR) emissions quantification and mitigation strategies.

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Yorke Engineering has assisted over 2,000 industrial and government facilities across California with EH&S consulting and air quality consulting, as well as permitting and compliance for storm water, wastewater, hazardous waste, industrial hygiene, and safety programs. Learn more here: Services – Yorke Engineering, LLC

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