Trends in New York State light-duty vehicle fleet composition: Emission standards and engine technology (2013–2025)

The United States Environmental Protection Agency (USEPA) established regulatory frameworks (Pre-Tier 2, Tier 2, and Tier 3) to address vehicle emissions. Simultaneously, a technological shift from port fuel injection (PFI) to gasoline direct injection (GDI) engines (began in 2007), has been underway. GDI has greater fuel efficiency, but potentially produces more secondary organic aerosol (SOA) under Tier 2 emissions than Tier 3. This study examined light-duty vehicle fleet transitions in New York State from 2013-2025, specifically the shift between engine technology and fleet turnover across emission tiers. Registration data from the New York State Department of Motor Vehicles were analyzed and vehicles classified into Pre-Tier 2, Tier 2, and Tier 3 based on Model Year, Vehicle Identification Number (VIN), and regulatory phase-in schedules. Manufacturer-reported statistics and VIN were used to categorize vehicles. New vehicles sold after 2007 had to meet Tier 2 standards, but only 53% of the total fleet were Tier 2 vehicles in 2013 suggesting lag time in fleet-wide penetration. Similarly, penetration of Tier 3 vehicles (introduced in 2017) was slower than expected. By 2025 only 36% of the fleet consisted of Tier 3 vehicles, and ∼6% were plug-in electric or hybrid vehicles. Meanwhile, GDI technology adoption increased rapidly and grew from 5% in 2013 to 36% in 2025. The slow fleet turnover highlights substantial lag between regulatory implementation and fleet composition changes. This lag resulted in continuing higher emissions and SOA formation indicating that air quality benefits from Tier 3 implementation will take longer to be realized. • Multiple policy actions were made to reduce emissions from light duty vehicles. • Engine technology (PFI to GDI) was changed to improve fuel efficiency. • Gasoline was reformulated to reduce benzene exposures. • Effectiveness of emissions policies depends on new vehicles entering the fleet. • Relatively slow penetration of Tiers 2 and 3 vehicles limit control effectiveness.