We then apply this estimate to quantify the long-term emissions implications of alternative scenarios for street-network sprawl. We find an elasticity of vehicle ownership with respect to street connectivity of –0.15-larger than suggested by previous research. We provide new estimates of the environmental impact of low-connectivity roads, characterized by cul-de-sacs and T-intersections, which we dub street-network sprawl. The location and interconnectedness of local roadways form a near permanent backbone for the future layout of land parcels, buildings, and transportation options.

We focus on the long-term nature of infrastructure decisions, specifically local roadways, which can lock in greenhouse gas emissions for decades to come. We quantify the importance of early action to tackle urban sprawl. 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. The cities of Portland, OR Seattle, WA and Vancouver, BC have adopted climate action plans with the goal of dramatically reducing GHG emissions. (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. 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. 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.

Vmt vehicle miles traveled