CARB Announces Public Workshop on Tier 5 Off-Road Diesel Engine Emission Standards Rulemaking



CARBThe California Air Resources Board (CARB) announced a new virtual public workshop regarding its upcoming off-road diesel engine Tier 5 rulemaking activities.

This rulemaking corresponds with CARB’s ongoing work to amend the current Tier 4 off-road diesel engine standards to help California comply with the EPA’s National Ambient Air Quality Standards (NAAQS). CARB staff are proposing drastic reductions of 90% and 75% to both NOx and PM, respectively, when compared to CARB’s Tier 4 emissions standards.  

During this two-day workshop, CARB staff will introduce and discuss various concepts from its latest proposal to reduce criteria pollutants and tailpipe greenhouse gas (GHG) emissions from new diesel engines. Some of these proposals will likely include:

  • Tier 5 implementation timelines
  • Criteria pollutant & GHG emissions standards
  • Off-road Low Load Cycle (LLC) for certification
  • Idling standards
  • Revised warranty and useful life requirements
  • Credit provisions
  • Among other important issues

These proposals are tentatively planned for official Board approval in the 2025 timeframe, with implementation dates starting in 2029 for certain engine families. It is crucial for industry stakeholders to participate in these discussions as much as possible. Through the AEM Engine Emissions Technical Committee (EETC), AEM intends on participating on these workgroup meetings and staying engaged throughout the rulemaking process to better understand CARB’s intentions and to ensure the industry’s voice is represented during these meetings. If you are interested in this topic, or participating on the EETC, please reach out to AEM’s Travis Webb or Jason Malcore at   

The Public Workgroup is scheduled for Oct. 30-31, 2023, from 8 a.m. PST – 5 p.m. PST.  We encourage all stakeholders to register for this workshop and participate on the call.

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