Mobile Source Program

Over 70% of the total air pollution in San Diego County is generated from mobile sources. The purpose of the Mobile Source Program is to reduce public exposure to diesel particulate matter (PM) and smog-forming Nitrogen Oxide (NOx) emissions from diesel-powered trucks, buses, and other heavy duty equipment.

What Mobile Equipment Is Regulated and How?

Smoking Truck
Dump Truck
School Bus
Shipping Containers
Off-road Vehicle

Commercial Trucks & Buses

Truck and Bus Regulation

Diesel-fueled trucks and buses greater than 26,000 lbs. must have a diesel particulate filter (DPF) installed or be approved for an exemption. Trucks and buses between 14,001 and 26,000 lbs. must upgrade to a 2010 or newer model year engine based on a compliance schedule.

Full Regulation

Regulation Overview

The Truck Stop: California Diesel Truck Info

Heavy Duty Vehicle Inspection Program

Heavy-duty trucks and buses are prohibited from emitting smoke over a certain opacity. DPF and DPF monitoring systems must be properly functioning and an emission control label (ECL) verifying that the engine has met Californian emission standards must be affixed to the vehicle's engine.

Full Regulation

Regulation Pamphlet

Commercial Vehicle and School Bus Idling

Diesel-fueled vehicles weighing more than 10,000 lbs. are prohibited from idling for greater than 5 minutes unless the engine meets a low-NOx idling emission standard and the truck is labeled with a "Cerified Clean Idle" sticker. This sticker is invalid when the truck is idling within a restricted area. School buses and other heavy duty vehicles must turn off the engine immediately upon arriving at a school and depart within 30 seconds of starting the engine.

Full Regulation (Commercial Vehicles)

Full Regulation (School Buses)

Regulation Fact Sheet


Diesel-fueled vehicles greater than 26,000 lbs. that transport cargo within ports and intermodal rail yards must meet engine emission standards. All drayage trucks must have a 2007 or newer model year engine.

Full Regulation

Regulation Fact Sheet

Off-Road Vehicles

Off-road vehicles that are diesel-powered, self-propelled, and 25 horsepower or greater must be registered under the current owner with the California Air Resources Board (CARB) Diesel Off-Road Online Reporting System (DOORS). Each vehicle is assigned an Equipment Identification Number (EIN) which must be labeled on both sides of the vehicle. Fleets must meet emission targets.

Full Regulation

Regulation Fact Sheet

Informational Flyer

Off-road Regulation Knowledge Center

Transportation Refrigeration Units (TRU) and TRU Gensets

Diesel-fueled TRUs that operate in California must meet in-use performance standards by the end of the 7th year after the engine model year. TRUs that are based in California must also register with CARB via the CARB Equipment Registration page (ARBER).

Full Regulation

Regulation Advisory

How Do We Ensure Compliance?

The California Health and Safety Code grants District staff the right of entry to conduct inspections and enforce air pollution regulations. District inspectors enforce mobile source requirements through unannounced inspections of on-road and off-road equipment. Inspections of mobile sources may also occur concurrently with inspections of permitted stationary equipment. A Memorandum of Understanding (MOU) was signed with CARB in 2014 designating which regulations the District will enforce. An updated MOU was signed in 2017 to allow the District to settle certain violation types. A Compliance Advisory was issued in 2016 to notify equipment operators of these inspections.

How Should I Respond to an APCD Citation?

For more information about District violations please see our Violation Information page.

Off-Road Vehicle Violations

Violation Recommended Action
Failure to Report Vehicle in DOORS Register the vehicle to your company in DOORS. If the vehicle has already been assigned an EIN you must move that EIN into your fleet. Vehicles should be registered within two weeks of the citation issuance.
Failure to Display EIN The EIN should be properly displayed on both sides of the vehicle. More information is available here. Send pictures of both sides of the vehicle with the labels in place to the Air Quality Inspector within two weeks of the citation issuance.

TRU Violations

Violation Recommended Action
Failure to Report TRU in ARBER TRUs based in California should register with CARB's Equipment Registration System (ARBER) within 14 days of the citation issuance.
Failure to Display IDN The Identification Number (IDN) of the TRU should be labeled on both sides of the unit. Send pictures of both sides of the TRU with the IDN properly labeled to the Air Quality Inspector within two weeks.
TRU Not Compliant with In-Use Standards Remove from service by following the steps outlined in this CARB Advisory or comply with in-use standard requirements within 30 days of the citation issuance. Send proof of compliance to the Air Quality Inspector.

How Can I Learn More?

CARB hosts informational trainings about these regulations at various locations throughout the year. To browse the training calendar navigate to the CARB training page, select Log In, then select "Prefer to browse first" under the New Students section.

CARB Course 521.7- Diesel On-Road Truck Rules

CARB Course 504 - Off-Road Diesel Vehicle Rules

What Incentives are Offered for Mobile Source Compliance?

For eligible mobile source operators, the District administers a number of grant programs for partially funding the replacement of older engines or vehicles with new, less polluting models. Learn more


Compliance Division Contact

Contact Us

If you have any questions, please contact the APCD Mobile Source Coordinator by email or phone at (858) 586-2677.