A Quantitative Investigation into the Impact of Partially Automated Vehicles on Vehicle Miles Travelled in California

Research Team: Scott Hardman (lead), Debapriya Chakraborty, and Eben Kohn

University: UC Davis

Problem Statement: Researchers estimate that, in 2018 alone, more than 140,000 partially automated electric vehicles were sold in the United States. Prior research has shown that these vehicles may already be impacting travel in the U.S. in ways that contradict the national goal of reducing vehicle miles traveled (VMT) and California’s goal of reducing greenhouse gas emissions, partly by reducing VMT. If automated electric vehicles lead to increased VMT, the positive benefits of electric vehicle introduction may be somewhat reduced, thus negatively impacting future transportation emissions. The California Air Resources Board notes that a 14.3% reduction in per capita VMT is needed to meet California’s goals of a 19% reduction in greenhouse gas emissions from passenger transportation by 2035 relative to 2005.

Project Description: This project investigated changes in travel behavior by owners of partially automated electric vehicles. Partial automation can control vehicle speed and steering using sensors that monitor the external environment. The researchers used review results from survey responses including 940 users of partial automation, of which 628 who have Tesla Autopilot and 312 with systems from other automakers. Autopilot users report using automation more than users of other partial automation systems. Autopilot has the largest impact on travel, notably 36% of Autopilot users reporting more long-distance travel. Respondents who are younger, have a lower household income, use automation in a greater variety of traffic, roads, and weather conditions, and those who have pro-technology attitudes and outdoor lifestyles are more likely to report doing more long-distance travel. The project used propensity score matching to investigate whether automation leads to any increase in respondents’ annual vehicle miles travelled. For simplicity, the researchers focused only on the impact of Tesla Autopilot and found that automation results in an average of 4,884 more miles being driven per year.

Status: Completed

Budget: $79,700

Project Partner(s): California Air Resources Board

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