TRUE publication

Development and application of a United States real-world vehicle emissions database

Remote sensing is an important tool for monitoring the real-world emissions of cars and trucks, and remote sensing data can be used to evaluate the effectiveness of emission control policies and identify emission defects and defeat devices. To complement its work on real-world emissions in Europe, TRUE has compiled remote sensing data from the states of Colorado and Virginia and the University of Denver to investigate the emissions of U.S. cars and trucks. The TRUE U.S. database includes nearly 60 million emissions records and is intended to support further research and the development of evidence-based emissions control policies in the United States.

Initial analysis of the database led to the following high-level findings regarding the U.S. fleet:

  • Over the past three decades, fleet-average emissions for nitrogen monoxide (NO), carbon monoxide (CO), and hydrocarbons (HC) have shown a significant downward trend and have remained particularly low after the phase-in of the U.S. EPA Tier 2 standards in the mid-2000s.
  • The NO emissions from light-duty vehicles increase with vehicle age as emission control technologies deteriorate. In older model years, the deterioration can exceed 0.2 g NO/kg fuel per year, an approximate median increase in emissions of 200% over the vehicle useful life defined in U.S. EPA emission standards. The rate of emissions increase declines with newer model years, suggesting that emissions deterioration is less pronounced in modern vehicles.
  • The contribution of the oldest light-duty vehicles in the fleet to total NO mass emissions has increased over time. In 2010, vehicles 15 years old and older made up approximately 14% of the fleet but were responsible for 50% of total NO mass emissions. By 2018, the percentage of the fleet responsible for 50% of total NO emissions had decreased to 11%.
  • Although there was a 94% reduction in heavy-duty vehicle NOx emissions from model year 2004 engines to model year 2016 engines, real-world emissions of most model years exceed EPA engine emission standards. Data show a considerable lag of 6 years or more between the adoption of EPA 2010 standards and the time when real-world emissions approached certification limits.