The transportation sector accounts for the largest portion of greenhouse gas (GHG) emissions compared to all other sectors, and GHGs are once again on the rise. At the same time, new mobility technologies are being introduced and fully autonomous vehicles (AVs) are anticipated to be deployed, at least to varying extents, within 5-10 years. (Waymo, Google’s self-driving project, is already operating a limited robotaxi service in Phoenix, AZ with a fleet of AVs.) AVs have the potential to improve safety, reduce congestion, and increase mobility— but they could also increase congestion, increase vehicle miles/ kilometers traveled (VMT/VKT), and erode transit, walk, and bike mode share, exacerbating existing conditions. The cities of Portland, OR; Seattle, WA; and Vancouver, BC have adopted climate action plans with the goal of dramatically reducing GHG emissions. This policy brief is intended to help the three cities better understand how AVs may help or hinder them in achieving their goals, and what recommended actions to take at this critical moment in time.

Key findings

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Research on AVs suggests that they are likely to increase VMT/VKT and congestion without policy intervention. AVs may also compete with transit since an AV trip may be cheaper than a ridehailing (e.g., Uber and Lyft) trip today as the labor costs associated with paying drivers will be dramatically reduced or eliminated.

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Thus far, AV technology is being incorporated into hybrid and electric vehicles rather than gasoline-powered ones. If electric AVs replace conventional, gasoline-powered vehicles, GHG emissions may be reduced—although the fuel mix of the local energy grid should be considered. AVs will likely share the road with conventional vehicles for years to come. If AVs contribute to increased VMT/VKT and congestion overall, GHGs are likely to rise.

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The compactness of the urban form is an important consideration in GHG emissions since the level of density and/or sprawl influences travel behavior. On the one hand, AVs have the potential to increase commute tolerance by freeing up time that would otherwise be spent behind the wheel. That may put additional pressure on sprawl if people are willing to commute longer distances in exchange for less expensive housing or more land. On the other hand, AVs may reduce demand for parking since passengers can be dropped off or picked up at their destination without the need to park. This could free up urban land to be redeveloped for other purposes such as affordable housing.

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Realizing the opportunities that AVs and other new mobility technologies hold will require a proactive approach by cities. Cities should continue working to enact policies that reduce reliance on the automobile overall by prioritizing active modes, and adopting a people-first approach. In working with the private sector, cities may benefit from identifying the desired outcomes first and encouraging private providers to find ways to achieve those outcomes. Smaller scale pilot projects can also help reduce risk and allow cities to evaluate initial outcomes as they work to identify the most effective policies. Additionally, cities should engage in regional collaboration and coordination to enhance leverage and maximize resources.

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