Mobile Source Program

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Over seventy percent of the total 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?

  • Commercial diesel-fueled trucks and buses
  • Transportation refrigeration units (TRUs)


School Bus
  • Diesel-fueled off-road equipment 25 horsepower (HP) or greater.
Off-Road Equipment - Water Truck

What Are The Regulations?

On-Road Equipment:

  • Regulated On-Road commercial heavy duty diesel trucks including drayage trucks and buses must meet the California Air Recourses Board (CARB) emission standards. An Engine Control Label (ECL) verifying that these emission standards are met must be affixed to the vehicle's engine. See CARB's Mobile Source's Page for additional information.
  • Transport Refrigeration Units are subject to emission standards.
  • Idling Restrictions: Heavy Duty commercial diesel vehicles with a GVWR of over 10,000 lbs and school buses are required to restrict engine idling.
  • If you would like to verify if a company or fleet has reported compliance with the Truck and Bus regulation to the Air Resources Board click here.
  • Truck and Bus Regulation- How to Verify if Hired Fleets Comply

Off-Road Equipment:

  • Regulated Off-Road equipment must be reported into CARB's Diesel Off-Road Online Reporting System (DOORS).
  • DOORS public information lookup- All vehicles subject to the Off-Road diesel-fueled fleets regulation should be labeled with Equipment Identification Numbers (EINs) by September 2009.  All EINs consist of six characters - two upper case letters, one number, one upper case letter, and then two numbers (for example, RH4M79). If you suspect a vehicle you observe has a fraudulent EIN, you can look up further information on the vehicle including vehicle type, and vehicle manufacturer. Enter the EIN in the box provided. Be sure to use uppercase letters. You can also verify if a company has a certification of compliance for their fleet.
  • DOORS User Guide - Public Info Look Up

Exhaust Smoke Opacity Requirements:

  • On-Road equipment must meet the requirements of the periodic smoke inspection program. For more information see here.

California Air Resources Board (CARB) Course 521.7- CARB Diesel On-Road Truck Rules

CARB Course 504 In-Use Off-Road Diesel Vehicle Regulation

How Do We Ensure Compliance?

Inspections: The San Diego Air Pollution Control District (District) signed a Memorandum of Understanding with the California Air Resources Board to enforce certain mobile source regulations.  District inspectors will enforce mobile source requirements through inspections of On-Road and Off-Road equipment at ports, highway patrol stops, places of business, etc. Additionally, inspections of mobile sources may occur concurrently with inspections of permitted stationary equipment. A Compliance Advisory was issued on 04/22/16 to notify equipment operators that the District will enforce certain mobile source regulations. 


Incentives Program

For Eligible Mobile Source operator applicants, 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

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