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The Environmental Protection Agency is proposing to modify the schedule for light-duty and medium-duty vehicles to meet Tier 4 criteria pollutant standards. The proposal targets model years 2027 and 2028. The agency is adjusting the phase-in schedule, which dictates how quickly manufacturers must reduce emissions as they introduce new vehicles into the market.

Why it matters: This action primarily affects vehicle manufacturers, importers, and converters who need to plan production schedules and compliance strategies for the 2027 and 2028 model years. Adjusting the phase-in schedule can change when specific emission requirements kick in, which may influence how quickly manufacturers transition their fleets toward lower-emission technologies. For the general public, the impact is indirect and depends on how these timeline changes affect vehicle availability and pricing.

Who it affects

  • Manufacturers of light-duty vehicles (passenger cars and light trucks).

This summary is based on a proposed rule published by the Environmental Protection Agency in the Federal Register; readers should consult the full document at Docket ID EPA-HQ-OAR-2025-3297 before relying on specific details.

Agency: Environmental Protection Agency
Source: Federal Register — read the official document

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