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 US light-duty vehicles.
FIA Foundation and the International Council on Clean Transportation (ICCT) established The Real Urban Emissions (TRUE) Initiative. The TRUE initiative seeks to supply cities with data regarding the real-world emissions of their vehicle fleets and equip them with technical information that can be used for strategic decision making. TRUE combines measurement techniques to produce a granular picture of the on-road emissions of the entire vehicle fleet by make, model, and model year.
The TRUE US 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. Analysis of the TRUE US remote sensing database revealed the following key findings regarding the makeup and emissions of the US 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 US EPA Tier 2 standards in the mid-2000s.
The NO emissions from light-duty vehicles of all model years 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 US EPA emission standards. The rate of emissions increase declines with newer model years, suggesting that emissions deterioration is less pronounced in modern vehicles.
Average fuel-specific NO emissions of gasoline light-duty vehicles and light-duty trucks per model year and vehicle age. Source: The ICCT.
Measured deterioration rates are much higher than projections submitted to the US EPA by manufacturers. The average manufacturer-reported deterioration rate is 0.009 gNOx/kg per year. This is about an order of magnitude lower than remote sensing deterioration rates for MY 2010 light-duty vehicles (0.09 gNOx/kg per year) and light-duty trucks (0.08 gNOx/kg per year).
For light-duty vehicles, the contribution of the oldest vehicles in the fleet to total NO mass emissions has increased over time. In 2010, vehicles 15 years old and older made up approximatively 14% of the fleet but were responsible of 50% of total NO mass emissions. By 2018, the percentage of the fleet responsible for 50% of total NO emissions had decreased to 11%.
The NO emissions distribution for heavy-duty vehicles has also become more skewed with time and the implementation of more stringent NOx engine emission standards. Between 2010 and 2018, the proportion of the oldest vehicles in the fleet contributing to 50% of total mass emissions decreased from 30% to 16%.
The analysis revealed a doubling of NO emissions for certain diesel pickup trucks under cold weather conditions. This finding warrants further investigation and highlights the value of remote sensing data in identifying vehicles with atypical real-world emissions performance.
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.
The US remote sensing data are consistent with other real-world emissions measurement techniques in showing elevated NOx emissions from diesel trucks under low-speed urban operating conditions.
Remote sensing campaigns continue to find that real-world emissions can be much higher than emission standards. As new data become available, the TRUE US database will be expanded, allowing for continued assessment of the real-world emissions of US cars and trucks to support further decision making and policy development to address fleet emissions.