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Regulations for Emissions from Vehicles and Engines

Cleaner Trucks Initiative

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The EPA Administrator announced in November 2018 that EPA would pursue the Cleaner Trucks Initiative (CTI) to update NOx emissions standards for heavy-duty trucks. The purpose of this webpage is for EPA to keep interested stakeholders apprised of our progress as we develop the CTI rule.

From 2007 to 2017, NOx emissions in the U.S. dropped by more than 40 percent. But there is more work to be done. Heavy-duty vehicles are the largest contributor to mobile source emissions of NOx and will be one of the largest mobile source contributors to ozone in 2025. EPA last revised NOx standards for on-highway heavy-duty trucks and engines in 2001. We have an opportunity to modernize the requirements to better reflect the capability of available emissions control technologies. In particular, emissions standards have lowered overall NOx emissions from heavy-duty trucks, but have not focused on emission control under low-load conditions—when trucks are at idle, moving slowly, or in stop-and-go traffic.

The Cleaner Trucks Initiative will work to ensure emissions reductions occur in the real world in all types of truck operation. Notably, this rulemaking offers opportunities to reduce ambient particulate matter and ozone across the country by reducing NOx pollution from heavy-duty trucks. EPA is also exploring ways to develop a smart program design that leverages modern and advanced technologies, while streamlining existing requirements.

In 2016, EPA received petitions for a rulemaking to address heavy-duty NOx from over 20 organizations including state and local air agencies from across the country. More information on the petitions and EPA's response can be found here.

Cleaner Trucks Initiative Process

EPA is identifying technologies capable of reducing criteria pollutant emissions from heavy-duty trucks, and developing the data and analyses needed to inform a comprehensive rulemaking. We are actively working with a range of stakeholders, including OEMs, suppliers, end-users, dealerships, labor, state/local/tribal governments, and environmental and health organizations. We intend to issue a proposed rulemaking in 2021.

On January 6, 2020, the Administrator signed an Advance Notice of Proposed Rule (ANPR) soliciting pre-proposal comments on the Cleaner Trucks Initiative.

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EPA Technical Projects to Inform the Cleaner Trucks Initiative

Below are technical projects, studies, and test programs EPA is conducting or contributing to as part of the CTI rulemaking. Note that EPA will rely on additional technical information available in the public domain during the rulemaking.

  • Heavy-duty diesel advanced engine and aftertreatment technology demonstration program. EPA is investigating cylinder deactivation and late intake valve closing as strategies that can reduce airflow and increase exhaust temperatures in diesel engines. These valvetrain technologies can help catalyst-based aftertreatment maintain effective emission control under low load operation, while reducing fuel consumption. EPA is also evaluating next generation aftertreatment configurations and formulations to improve catalyst performance across a broader range of engine operating conditions. These technology assessments are being performed at EPA’s National Vehicle and Fuel Emissions Laboratory (NVFEL) and Southwest Research Institute (SwRI).
  • Heavy-duty gasoline demonstration program. Gasoline engines continue to play an important role in the heavy-duty market for some applications. EPA is evaluating strategies to accelerate light-off and keep the three-way catalyst warm for improved cold start and low-load emissions, and material improvements that can reduce the need for engine protection modes that increase emissions during high-load operation. These technology assessments are being performed at NVFEL and SwRI.
  • Diesel aftertreatment accelerated aging program. EPA is aware of stakeholder concerns that the current emissions durability demonstration process is time consuming, costly, and risky for manufacturers, yet can underestimate the real-world deterioration of the emissions system. EPA is developing a pathway for demonstrating aftertreatment durability through an accelerated catalyst aging procedure. Testing for this program is being performed at SwRI.
  • Aftertreatment cost teardown. EPA is conducting a technology teardown study to examine an advanced selective catalytic reduction aftertreatment system. This work will identify all component systems and include an engineering evaluation and cost analysis of the aftertreatment package. This study will build on methodology adopted and peer-reviewed for light-duty vehicle technologies.
  • Medium-duty diesel vehicle baseline studies. EPA is following full-vehicle testing performed by Environment and Climate Change Canada that is evaluating the performance of advanced technologies available in the market today. EPA expects this study will inform our baseline engine performance for medium-heavy duty engines.
  • NOx sensor performance program. Onboard NOx sensors could potentially play a key role in an updated in-use testing program and it is critical that EPA understand today’s sensor performance. EPA is beginning a study to assess the accuracy, repeatability, noise, interferences and response time of current NOx sensors.

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EPA Publications and Papers Informing the Cleaner Trucks Initiative

Below are links to recent technical publications and papers by EPA that may inform the CTI rulemaking. This is not a comprehensive list of publications that will be referenced in this rulemaking.

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EPA Presentations Regarding the Cleaner Trucks Initiative

Below are links to technical presentations by EPA that describe the CTI rulemaking, or related work that may inform the CTI rulemaking. These materials are shared with the intention of keeping all stakeholders informed of the work underway on the CTI rulemaking.

CTI Technical and Overview Presentations
CRC Real World Emissions Workshop Presentations
MOVES Review Work Group Presentations
All MOVES Review Work Group presentations listed below are available EPA’s MOVES Model Review Work Group page.
  • “Updates to MOVES Heavy-Duty Running Exhaust Rates: Diesel, Gasoline, and CNG”, MOVES Review Workgroup, April 2019.
  • “Modeling of Gliders in MOVES”, MOVES Review Workgroup, April 2019.
  • “Heavy-Duty Vehicle Activity in MOVES: Idle, Starts, Soaks, and Hotelling”, MOVES Review Workgroup, June 2018.
  • “Updates to MOVES HD Source Masses using VTRIS”, MOVES Review Workgroup, December 2017.
  • “Updates to HDV Fixed Mass Factor and Diesel PM Rates”, MOVES Review Workgroup, December 2017.
  • “Heavy-Duty Start Emission Rates”, MOVES Review Workgroup, June 2017.
  • “Vehicle Idle Activity in MOVES”, MOVES Review Workgroup, March 2017.
  • “Update to Running Exhaust Criteria Pollutant Emission Rates for Model Year 2010+ Heavy-Duty Diesel Vehicles”, MOVES Review Workgroup, December 2016.
  • “Updated Emission Rates for Extended Idle and Auxiliary Power Unites”, MOVES Review Workgroup, December 2016.

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