By Scott Hardman, Gil Tal, and Dan Sperling
Driverless cars will almost certainly lead to much greater travel, assuming they are personally owned, as most cars are today. But what about vehicles on sale today that already have partial automation? Will people use these cars differently? Will they drive them more than non-automated vehicles? Are they part of the reason traffic congestion is worsening? Early evidence suggests the answer could be yes.
Many major automakers offer cars with partial automation, including Tesla with Autopilot, Cadillac with Supercruise, and Nissan with Pro Pilot Assist. These technology packages can control speed, braking, and acceleration; keep the car in a lane; and allow the car to overtake slower traffic—all without driver input. These cars essentially drive themselves in certain conditions (such as on freeways), with the caveat that the human driver is still in control and alert. The systems monitor alertness by sensing whether the driver has at least one hand on the steering wheel (though they don’t have to steer), or with a camera that ensures the driver is looking at the road ahead.
In a recent study, we surveyed drivers in the United States who owned Tesla electric cars outfitted with Autopilot, Tesla’s partial automation technology package. Of these drivers, we found that Autopilot users are clustered into four groups: very frequent users, frequent users, semi-frequent users, and infrequent users. Very frequent users report using Autopilot on 90% of their trips regardless of road type, weather conditions, or traffic conditions. Frequent users engage automation on close to 80% of their trips and are more pragmatic in their usage, being most likely to use it on freeways, in clear weather or rain (but not fog or snow), and in both congested and free-flow traffic conditions. Semi-frequent users are more cautious, using Autopilot on around 40% of trips, and only on freeways in clear weather. Infrequent users are the most cautious, using automation for only a quarter of trips, and only on freeways without traffic in clear weather.
Total vehicle usage varies significantly between these users, as indicated in the figure below. We found that frequent and very frequent uses of Autopilot drive many more miles per year compared to other drivers, logging 4200-5700 more miles than other Tesla owners, and 3300 more than drivers in vehicles less than five years old.
Partially automated cars (Teslas with autopilot) are driven 22% more miles (annually) than the average for vehicles less than 5 years old, and 38% more than Tesla cars without autopilot
UC Davis Institute of Transportation Studies
We suspect this large increase in car travel is the result of drivers feeling more relaxed, less stressed, and less tired, which makes them more willing to spend time in their car. However, we cannot rule out the role of other factors in increasing miles, such as the lower cost of driving an electric car, the comfort and refinement associated with a luxury car, or self-selection. Nor can we rule out the possibility that the need for increased travel is the cause of frequent Autopilot use, rather than vice versa.
These findings are not definitive. More research is needed to determine the causal relationship, but based on this survey and ongoing research, we hypothesize that the use of partial automation will increase the amount that consumers drive. We are less confident of the magnitude of the increase.
This potential for partial automation to increase vehicle use is important, especially as policymakers grapple with traffic congestion, energy use, climate change, and local air pollution. Given that the benefits of partial automation (e.g., increased safety and comfort) apply principally to car drivers, and the costs (e.g., congestion and pollution) apply to the entire population, there is more urgency for public action. What is the best way to encourage innovation, while protecting the public interest? Perhaps most compelling is the use of road pricing to internalize the additional cost of congestion and energy use.
This blog is based on findings in the publication: Hardman S, Lee JH, Tal G. How do drivers use automation? Insights from a survey of partially automated vehicle owners in the United States. Transportation Research Part A: Policy and Practice 2019;129:246–56.
Scott Hardman, Ph.D. is a researcher at the Plug-in Hybrid & Electric Vehicle Research Center of the Institute of Transportation Studies at the University of California Davis (ITS-Davis). His focus is on electric vehicles (EVs) and automated vehicles (AVs). This includes understanding the buyers of EVs & AVs, consumer preferences and purchase motivations, how consumers use the vehicles, and researching policies to manage the adoption of both technologies. See his research here. Follow on Twitter: @scottiehardman.
Gil Tal, Ph.D. is director at the Plug-in Hybrid & Electric Vehicle Research Center and transportation research director at the China Center for Energy Transportation, both at the Institute of Transportation Studies at the University of California Davis (ITS-Davis). He focuses on travel behavior and the implementation of travel behavior related policies. See his research here.
Dan Sperling, Ph.D. is the Distinguished Blue Planet Prize Professor of Engineering and Environmental Science at the University of California, Davis, director of ITS-Davis, and lead author of Three Revolutions: Steering Automated, Shared, and Electric Vehicles to a Better Future. Follow on Twitter: @DanSperling_ITS, @ITS_UCDavis, @3Rev_ITSDavis.
