Light-Duty Vehicle Research
The impact of light-duty vehicles on statewide greenhouse gas emissions and criteria pollutants is large and many regulatory measures are in place to mitigate these impacts. Real-world vehicle operations need to be understood and measured to better characterize the impact that they have on emissions control deterioration, fuel consumption, activity characteristics, and high emissions over the vehicle's useful lifetime. Additionally, improving fuel economy and adopting zero-emission vehicles require research that helps in achieving air quality improvement and GHG reduction goals. Below is a list of some major projects being undertaken as part of the Vehicle Emissions Research Program at CARB focusing specifically on light-duty vehicles.
On-road light-duty vehicle emissions measurements using remote sensing devices
In order to evaluate the effectiveness of various regulations in reducing real-world vehicular emissions, and to identify any egregious emission issues in the real world, CARB needs a substantial set of long-term, real-world vehicle emission measurement data. Continued measurements of on-road light-duty vehicle (LDV) exhaust emissions in real-world conditions is key to monitoring the emission trends over time and to verifying the effectiveness of the California emission regulations.
In California, on-road LDV exhaust emissions have been measured successfully using roadside remote sensing devices (RSDs) at a West Los Angeles location every few years since 1999. They were conducted by the University of Denver (DU), and the most recent was completed in 2021 under a new CARB new research contract. This contract also sponsored similar sampling campaigns in Stockton and Fresno in 2021. The Fresno campaign was also sponsored by the CRC, and a Final Report with these results has been published on the CRC website.
These measurements provide a longitudinal record consisting of large sets of vehicle emission data. Real-world emission factors of carbon monoxide (CO), hydrocarbons (HCs), and oxides of nitrogen (NOx) from LDV have decreased by 75-85% between 1999 and 2018, but the contribution of the highest-emitting vehicles (i.e., the top 1%) to the total emissions have significantly increased, for example, from 26% in 1999 to 42% in 2018 for HCs. (Note that the total HC emitted by the top 1% decreased by 67% during this time period.)
The findings from these RSD measurement studies demonstrate the effectiveness of California’s emission control programs for LDV, and highlight the importance of continued mitigation of emissions from high-emitting vehicles.
The publications below present data form these projects. Also, all data collected can be accessed on the Denver University website.
Zhan et al., Atmos. Environ. (2020)
Bishop, JAWMA (2019)
Collection of Real-world Light-Duty Activity Data
Meeting California’s ambitious greenhouse gas (GHG) emissions goals will require real-world data on vehicular fuel consumption, engine duty cycles, and braking activity. A small pilot study has been conducted in which volunteers collect on-board diagnostic (OBD) and GPS data, either using dedicated OBD dataloggers or inexpensive wireless OBD transmitters that use smartphones as loggers. This data has been used to address questions regarding the benefits regenerative braking and the characteristics of engine start events, among others. These loggers have also been used to sample Transportation Network Company drivers in the development of the Clean Miles Standard.
Related Study on Plug-in Electric Vehicle Household Study
Other Projects and Research
Light-Duty Gasoline Vehicle (LDGV) High-PM Emitters
On-Road Vehicle Emissions Measurements with Remote Sensing Devices (RSD)
On-Road Measurement of Light-Duty Gasoline and Heavy-Duty Diesel Vehicle Emissions