Diesel Emissions - Mobile Equipment

Heavy Trucks:

Both on-road and off-road diesel powered vehicles and equipment are regulated by California Air Resources Board (CARB). On-road trucks greater than 14,000 lbs and off-road diesel equipment are required to meet numerical emissions limits for PM10. Offering an older diesel powered vehicle for sale within the state of California also has significant restrictions as does adding one to your fleet. If you intend to purchase or sell a diesel powered vehicle, please notify UCSF Environmental Programs.

Off-Road Diesels: 

On July 26, 2007, the Air Resources Board (ARB) adopted a regulation to reduce diesel particulate matter (PM) and oxides of nitrogen (NOx) emissions from in-use (existing) off-road heavy-duty diesel vehicles in California. Such vehicles are used in construction, mining, and industrial operations.

All self-propelled off-road diesel vehicles 25 horsepower or greater used in California and most two-engine vehicles (except on-road two-engine sweepers) are subject to the Regulation for In-Use Off-Road Diesel Fueled Fleets. This includes vehicles that are rented or leased.

The Off-Road regulation applies to self-propelled off-road vehicles (a.k.a. equipment or machines) with diesel-fueled or alternative diesel fueled (including biodiesel) engines that are 25 horsepower (hp) or greater. The vehicle is considered an off-road vehicle if it cannot be registered and driven safely on-road or was not designed to be driven on-road (this includes vehicles that were designed/manufactured for off-road use, but have since been modified so it can be driven safely on-road). The Off-Road regulation also applies to several types of on-road vehicles, such as workover rigs, and many two-engine vehicles. Vehicles that are covered by the Off-Road regulation include, but are not limited to: aerial lifts, aircraft tugs, backhoes, baggage tubs, belt loaders, cargo loaders, crawler tractors (bulldozers or dozer), excavators, forklifts, graders, loaders, mowers, rollers, rough terrain forklifts, rubber tired loaders, scrapers, skid steer loaders, snow blowers, tractors, trenchers, two-engine vehicles (may have on-road drive engines), workover rigs (may have on-road drive engines).

If you have any of the above equipment, please contact EH&S Environmental Programs to get your vehicles registered.

To learn more about the Off-Road Diesel-Fueled Equipment Program, please visit https://www.arb.ca.gov/msprog/ordiesel/ordiesel.htm and https://www.arb.ca.gov/msprog/ordiesel/faq/overview_fact_sheet_dec_2010-final.pdf

Portable Diesels:

Portable diesel-fueled engines having a rated brake horsepower of 50 and greater (≥ 50 bhp) “Portable” means designed and capable of being carried or moved from one location to another. Indicia of portability include, but are not limited to, wheels, skids, carrying handles, dolly, trailer, or platform. Examples of portable diesel equipment include air compressors, generators, concrete pumps, tub grinders, wood chippers, water pumps, drill rigs, pile drivers, rock drills, abrasive blasters, aggregate screening and crushing plants, concrete batch plants, and welders.

Particulate matter emission from diesel-fueled engines was identified as a toxic air contaminant in 1998, and this Airborne Toxic Control Measure (ATCM) is one of several control measures developed since then to reduce the toxic health risk associated from exposure to these emissions. The ATCM fleet standards became effective in January 2013, and will become progressively more stringent in January 2017 and in January 2020. In by requiring newer engines and cleaner engine technologies this regulation is part of the State’s Diesel Risk Reduction Plan to reduce diesel particulate matter.

Contact EH&S Environmental Programs to get your equipment registered and your fleet emissions calculated. Each fleet is subject to and shall comply with the following weighted PM emission fleet averages expressed as grams per brake horsepower-hour (g/bhp-hr) by the listed compliance dates:

Fleet Standard Compliance Date

Engines <175 hp (g/bhp-hr)

Engines 175 to 750 hp (g/bhp-hr)

Engines >750 hp (g/bhp-hr)














In 2008, CARB passed regulations that significantly restrict idling times of diesel trucks and off-road diesel vehicles. Heavy duty trucks greater than 10,000 lbs and off-road diesel vehicles consisting of tractors, trenchers, street sweepers, cranes, forklifts, or other diesel powered equipment are prohibited from idling > 5 min. Idling in excess of 5 min is allowable only under the following circumstances:

  • You are stuck in traffic.

  • When idling is necessary for inspecting, testing, repairing, or servicing your vehicle.

  • You need to verify that the vehicle is in a safe operating condition.

  • You are operating a power take-off device.

  • You cannot move because of adverse weather conditions or mechanical failure.  

  • You are queuing (must be beyond 100 feet from any residential area).

  • Your truck’s engine meets the optional NOx idling emission standard and your truck is located beyond 100 feet from any residential area.

  • You need to accomplish work for which the vehicle was designed (such as operating a crane).

  • It is necessary to bring the machine system to operating temperature.

  • It is necessary to ensure safe operation of the vehicle.

Idling Limit – No vehicles or engines subject to this regulation may idle for more than 5 consecutive minutes. Idling of a vehicle that is owned by a rental company is the responsibility of the renter or lessee, and the rental agreement shall so indicate.

View CARB’s Policy on Idling: https://www.arb.ca.gov/enf/advs/advs377.pdf