Maryland Pushes Back Against EPA Plan To Postpone Tier 4 Vehicle Emissions Standards

NOTE: The Maryland Office of the Attorney General shared the following press release:

BALTIMORE, MD – Attorney General Anthony G. Brown joined a coalition of attorneys general and cities in submitting a comment letter to the U.S. Environmental Protection Agency (EPA) opposing its proposed rule to delay implementation of the Tier 4 emissions standards for light-duty and medium-duty vehicles.  

If finalized, the EPA’s proposal would give manufacturers two additional years before they have to begin implementing these health-protective standards. Under the current, state-of-the-art “Tier 4” standards, which the EPA adopted in 2024, manufacturers must ensure that vehicles emit fewer harmful pollutants, including nitrogen oxides, particulate matter, hydrocarbons, and carbon monoxide. When it adopted these standards in 2024, the EPA gave manufacturers sufficient lead time before the standards would begin to be phased in and several additional years before full implementation of the standards is required. In accordance with this schedule, manufacturers are required to start implementing the standards with their model year 2027 vehicles and will have to obtain Tier 4 certification for all light-duty vehicles by 2030 and for all medium-duty vehicles by 2031. Now, the EPA has proposed to delay the start of this phase-in schedule for two years, which would delay the health protections the standards provide. 

In the comment letter, the coalition asserts that the EPA’s proposal to delay this compliance schedule, such that manufacturers are not required to take any action until they begin producing model year 2029 vehicles, would harm public health and welfare by delaying the benefits of stricter air pollutant emissions standards.  

Air pollution from motor vehicles continues to impact public health, welfare, and the environment. Motor vehicle emissions contribute to ozone, increased levels of particulate matter, and air toxics, which are linked to premature deaths and other serious health impacts, including respiratory illness, cardiovascular problems, and cancer. The Tier 4 standards take important steps towards reducing these public health burdens. The EPA projected that the final rule’s reductions of greenhouse gases, criteria pollutants, and air toxics would result in $270 billion net benefits by 2055 and would eliminate 410 million metric tons of carbon dioxide, 36,000 tons of nitrogen oxides, 8,700 tons of particulate matter, and 2,300 tons of benzene that otherwise would have been emitted by vehicles.  

Under the Trump administration, the EPA has already repealed federal greenhouse gas standards for vehicles, and a coalition of states – including Maryland – local governments, and regulatory agencies are currently challenging that action in court. Now the EPA seeks to delay the implementation of criteria and toxic pollutant standards, which would similarly erase important health and welfare benefits. 

In the letter, the attorneys general and cities assert that:  

• The EPA has failed to support with any evidence its claims that compliance with the Tier 4 standards is infeasible. In fact, the Tier 4 standards are still feasible and cost-effective based on the lengthy phase-in schedule and the flexible compliance pathways outlined in the 2024 rule, including low-cost, off-the-shelf controls for internal combustion engines.  
• The EPA failed to conduct any air quality modeling, nor did the EPA make any attempts to consider the economic value of the negative impacts of delaying the Tier 4 standards on air quality, and, by extension, public health and welfare.  
• The Clean Air Act does not allow the EPA to reverse course and weaken criteria and toxic air pollutant standards. It also does not authorize the EPA to make it harder for states to meet federal air quality standards. Thus, this proposal, if finalized, would be unlawful.  

In submitting the comment letter, Attorney General Brown joins the attorneys general of California, Colorado, Connecticut, Delaware, the District of Columbia, Hawaiʻi, Illinois, Maine, Massachusetts, Michigan, Minnesota, New Jersey, New York, North Carolina, Oregon, Rhode Island, Washington, Wisconsin, and the Chief Legal Officers of the City of Chicago, Illinois; the City of New York, New York; the City and County of Denver, Colorado; and the City and County of San Francisco, California.