On May 14, 2026, the EPA proposed delaying Tier 4 by two model years, citing industry feasibility concerns. This is Part 1 of a two-part review; Part 2 may result in permanent changes to or elimination of the standards entirely. The proposed delay means millions more vehicles will be sold at higher pollution levels that we already know cause preventable illness and death.

Transportation is the largest source of greenhouse gas emissions in the U.S. and a leading contributor to harmful air pollution, with communities of color and low-income communities bearing the greatest burden. Delaying cleaner standards extends and deepens these inequities for another generation.

The current proposed delay quantifies only the cost to industry of complying with Tier 4 standards. It does not quantify the cost to the public of delaying them — no accounting of premature deaths, asthma attacks, hospitalizations, or lost workdays that will now occur. EPA produced those numbers two years ago. Choosing not to include them now is a values decision, not a technical one.

It’s essential that we oppose the proposed delay and call on EPA to implement Tier 4 standards on schedule in model year 2027. Submit your comment now to protect this vital regulation.

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