Introduction: The California Air Resources Board (ARB) has proposed a new regulation aimed at reducing emissions of diesel particulate matter (PM), oxides of nitrogen and greenhouse gases from in-use, on-road diesel-fueled vehicles.

The regulation is still preliminary and there is no currently scheduled ARB meeting to consider or decide whether to actually implement the new regulation, which is still in the public comment period. The next scheduled public meetings on the proposed regulation are as follows: August 22 in El Monte. August 23 in Sacramento. August 28 in Fresno. For further information or to contribute public comments, please visit

As the regulation develops, this blog page will provide updates, especially if and when the regulation seems poised to pass. Below is a brief summary of the regulation in its current form:

Scope: The regulation applies to all heavy duty diesel-fueled or alternative diesel-fueled vehicles with engines model-year 2006 and older, and gross vehicle weight rating greater than 14,000 pounds that operate on streets or highways in California. While currently not included in the regulation, there are indications that future drafts will include cranes (on and off road) as needing to comply.

The regulation affects all persons, businesses or governments who own, lease, rent or sell such a vehicle in California, except that persons who provide financing for leases are not subject to the regulation. It also affects all vehicles intended to be on-road vehicles that otherwise fit the criteria, regardless of whether they are actually used on-road.

Summary of Requirements: Owners are required to keep each regulated vehicle in compliance for the entire time that the owner operates the vehicle in California. Each regulated vehicle fleet must:

  • Comply with best available control requirements (BACT). As an alternative to BACT requirements, an owner can use "fleet averaging.
  • Follow proper labeling procedures.
  • Comply with record-keeping requirements.

The regulation is intended to limit emissions of greenhouse gases, but currently does not have any specific provisions in this regard. The regulation is still subject to future consideration of the "strategy to reduce greenhouse gas emissions."

The regulation is currently separated into two phases, with the goal apparently to retire or "phase out" older engines over time. In fact, retiring older vehicles appears to be the most effective way of complying with the regulations at least in the first few years, after which the use of control technology and alternative fuels may be the best strategy. Phase 1 emission requirements start in 2009 (for pre-1994 engines) and end in 2013 (for 2003-2006 engines). Phase II requirements start in 2017 (for pre-2003 engines), and end in 2019 (for 2005-2006 engines).

Exemptions: Currently, certain vehicles are expressly exempted from this regulation (though they are likely covered by other environmental laws and regulations). These are:

  • Solid waste collection vehicles
  • Vehicles subject to the public agency and utility fleet rule
  • Heavy duty drayage trucks
  • School buses owned by a public school district
  • Military and tactical support vehicles
  • Emergency vehicles
  • Off-road vehicles
  • Historic vehicles