Emissions Impact of Connected and Automated Vehicle Deployment in California

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The transportation sector is undergoing a rapid transformation towards connected and automated vehicles (CAVs)—vehicles that communicate with roadway infrastructure and other vehicles and those able to drive without a human driver on-board. CAVs are expected to deliver many benefits for the transportation system and for vehicle occupants including safety improvements, travel cost reductions, and increased productivity while traveling.  For all these reasons, CAVs are anticipated to be a very attractive means of travel, and they will likely increase travel demand and vehicle miles traveled (VMT), which may lead to increased energy consumption and greenhouse gas (GHG) and criteria pollutant emissions. The exact impacts of CAVs will be determined by how these vehicles are designed, adopted, and utilized.

This study examined the existing literature on the expected impacts of CAV deployment on travel demand, gathered feedback through a workshop with leading experts in the field, and explored several California scenarios of light-duty CAV vehicle technology adoption, usage preferences, and policies in 2050 to estimate the associated VMT and resulting criteria pollutant and GHG emissions. Using a set of modifications in the California Statewide Travel Demand Model (CSTDM), the following scenarios were examined:

0) baseline (i.e., no CAVs);
1) private (i.e., privately-owned) CAVs;
2) private CAVs plus pricing;
3) private CAVs as zero-emission vehicles (ZEV);
4) shared (i.e., fleet-owned) CAVs;
5) shared CAVs plus pricing; and
6) shared CAVs as ZEVs

For each scenario, the travel demand and mode share outputs from CSTDM were used in combination with emission factors to project GHG and criteria pollutant emissions.

The results indicate that for both the “private CAVs” and “shared CAVs” scenarios the mode shares of public transit and air travel will likely sharply decrease, while total vehicle miles traveled and emissions will likely increase due to the relative convenience of CAVs, especially if no additional policies are implemented to contain the growth in car travel. Both pricing scenarios show a reduction in VMT is possible highlighting how road congestion and other pricing policies could at least in part offset the expected increases in VMT from CAVs. Finally, the electrification of CAVs would lead to eliminating the tailpipe vehicle emissions. However, other externalities, such as traffic congestion, would persist. In conclusion, policies such as pricing strategies and electrification can counteract and mitigate some of the undesirable impacts of CAVs such as pollutant emissions, though they will likely not be able to completely offset the increases in travel demand and road congestion that might result from CAV deployment. Results from this study will help inform CARB’s policies related to Senate Bill 375 and California’s broader CAV policies.

This study also reveals limitations in models like the CSTDM that primarily use sociodemographic factors and job/residence location as inputs for the simulation of activity participation and tour patterns, without accounting for some of the disruptive effects of CAVs. Thus, these models seem unable to account for certain changes in travel behaviors that might be expected when CAVs become available in the future, leading to the potential underestimation of the induced demand associated with CAV deployment.



Giovanni Circella headshot

Giovanni Circella, Ph.D., is the Director of the 3 Revolutions Future Mobility Program and the Honda Distinguished Scholar for New Mobility Studies at the University of California, Davis, and a Senior Research Engineer in the School of Civil and Environmental Engineering of the Georgia Institute of Technology. His expertise includes travel behavior, emerging mobility services, travel demand modeling and travel survey methods. Dr. Circella’s recent research has focused on the impacts of information and communication technologies, shared mobility, micromobility, vehicle automation and the COVID-19 pandemic on travel behavior and auto ownership, and the evolving lifestyles and mobility patterns of various population segments (e.g. “millennials”) in various regions of the U.S., Europe, South America and the Middle East. He is actively involved in the Transportation Research Board and serves as Chair of the Committee on Information and Communication Technologies and Transportation. He also serves as an elected member of the Executive Board of the International Association for Travel Behaviour Research. He received his Ph.D. in Infrastructure Engineering and Transportation Planning from the Technical University of Bari (Italy), his M.S. in Agricultural and Resources Economics from the University of California, Davis, and his Italian Laurea (B.S. plus M.S. equivalent) degree in Civil Engineering from the Technical University of Bari (Italy).

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