Answers to Your Questions about Greenhouse Gas, Tier 3 Vehicle Standards

By Glade Sowards

emission standardsUPDATED: 4/10/2020

On March 31, 2020, EPA finalized its Safer Affordable Fuel Efficient (SAFE) Vehicles Rule, which revised greenhouse gas (GHG) and corporate average fuel economy (CAFE) standards for light-duty vehicles.  Division of Air Quality (DAQ) staff received questions from the public about how this action might affect air quality in Utah and state efforts to meet federal air-quality standards in nonattainment areas.

While the revised standards may limit progress in reducing greenhouse gas (GHG) emissions, DAQ cannot make a comprehensive determination of those impacts on the emissions that contribute to Utah’s winter and summer air-quality challenges until EPA has updated its mobile source emissions model to reflect those revisions.

What are the standards in question?

In 2012, EPA established the second phase of light-duty vehicle greenhouse gas (GHG) standards covering model years (MY) 2017-2025. Like the Phase 1 standards (which covered MY 2012-2016 vehicles), the Phase 2 standards were established in parallel with National Highway Traffic Safety Administration (NHTSA) corporate average fuel economy (CAFE) standards, since vehicle GHG emissions largely correspond with fuel consumption. The Phase 2 GHG/CAFE standards are shown in Table 1 below, with the years affected by EPA’s April 2, 2018, action shaded in blue.

Table 1 – Projected 2017-2025 Fleet-Wide CO2 and Fuel Economy Compliance Levels

As part of the Phase 2 rulemaking, EPA conducted a Midterm Evaluation (MTE) of the standards for MY 2022-2025 to ensure that market conditions and technological developments remain conducive to achieving the GHG targets for those years. On January 12, 2017, former EPA Administrator Gina McCarthy completed the required MTE by signing a final determination to maintain the proposed GHG standards for MY 2022-2025.

On March 15, 2017, newly-appointed EPA Administrator Scott Pruitt announced his intent to reconsider former Administrator McCarthy’s final determination and make a new final determination by no later than April 1, 2018. The new final determination, signed on April 2, 2018, found that the MY 2022-2025 standards were “not appropriate” and should be revised.

On March 31, 2020, EPA and NHTSA announced a final rule revising the GHG/CAFE standards. The SAFE Vehicles Rule applies to model years 2021-2026.  As indicated, the final rule not only revised the existing GHG/CAFE standards for MY 2021-2025, but also finalized a new standard for MY 2026 as well.  The final rule GHG and CAFE estimated requirements are summarized in Table 2 below with the revised and new standards shaded in blue.  Because the final rule also made changes to the way GHG and CAFE targets are quantified, it is not possible to directly compare the compliance levels in Tables 1 and 2.  However, according to EPA and NHTSA, “The final rule will increase stringency of CAFE and CO2 emissions standards by 1.5% each year through model year 2026, as compared with the standards issued in 2012, which would have required about 5% annual increases.”

Table 2 – Projected 2017-2026 Fleet-Wide CO2 and Fuel Economy Compliance Levels

Does this impact Tier 3 vehicle standards?

While the Phase 2 GHG standards cover the same MY 2017-2025 time period as the Tier 3 vehicle standards, they are, in fact, separate standards with different aims. The GHG standards address carbon dioxide (CO2) emissions, with targets expressed in grams/mile. These targets coincide with CAFE fuel economy requirements, which are expressed in miles per gallon (mpg).

By contrast, the Tier 3 vehicle standards are aimed at reducing non-GHG emissions, such as directly emitted particulate matter (PM), nitrogen oxides (NOx), and nonmethane organic gas (NMOG), pollutants that contribute to particulate, ozone, and other air-quality problems. The Tier 3 vehicle standards, like the GHG standards, establish emission limits for these pollutants in grams/mile. The Tier 3 standards, shown in Table 3 below, are between 70 and 80 percent cleaner than the Tier 2 standards that came before them.

Table 2 – Tier 3 Certification Bin Standards (FTP; 150,000 miles)

Emission standards

Fuel consumption typically increases with vehicle size, so GHG emissions tend to be higher for larger vehicles like trucks and SUVs. However, due to the tremendous strides made in vehicle emission-control equipment over the past 50 years, emissions of non-GHG pollutants, such as direct PM, NOx, and NMOG, have become somewhat decoupled from fuel economy, to the extent that even larger SUVs and trucks are capable of meeting the stringent emissions limits established under Tier 3.

How will changes to the light-duty vehicle GHG standards impact Utah’s air quality?

Because the Tier 3 standards are independent of the GHG/CAFE standards, vehicles sold under the revised GHG and CAFE targets will still be subject to the pollutant emission limits established under Tier 3. Specifically, manufacturers will still be required to meet both the 30 mg/mile fleet average requirement for combined NMOG and NOx emissions and the 3 mg/mile per vehicle requirement for PM emissions — pollutants that contribute to Utah’s wintertime particulate and summertime ozone challenges. This means that if manufacturers choose to produce vehicles that consume more fuel as allowed under the revised GHG/CAFE standards, they will have to include more robust emissions controls sufficient enough to meet the Tier 3 mg/mile standards despite the increase in fuel combustion.  This gives us a degree of optimism that the impact of the revised GHG/CAFE on Utah’s air quality will be limited.  However, DAQ uses EPA models to calculate mobile source emissions, and until EPA has updated those models to reflect these revisions, DAQ cannot estimate the ultimate air quality impact of the revised GHG standards. Regardless, DAQ remains committed to protecting and improving Utah’s air quality and will continue its ongoing efforts to address Utah’s air-quality challenges.

Want to know more? Visit the EPA site for more information on the Safer Affordable Fuel Efficient (SAFE) Vehicles Final Rule.


Glade Sowards

I am an environmental scientist in the Division of Air Quality  Policy Section. I have a B.A. in Economics and Environmental Studies from Grinnell College and an M.S. in Forestry from Michigan Technological University. I worked at the Utah Energy Office for seven years before coming to work at DAQ. I enjoy playing music, road trips, camping, pack rafting, and hiking with my wife, Elizabeth, and our dog, Whiskey.