Economists have long understood the strong correlation between an economy’s performance and the overall vehicle miles traveled (VMT) in that region. VMT, which is also affected by gas prices, serves as a reasonable proxy for potential congestion. In the United States, given expectations for GDP growth, the US Census Bureau data indicates there may be a 1 percent CAGR for VMTs through 2030—a 14 percent gain, or a 500 billion mile increase.1
1 United States Census Bureau. (2016). “American Community Survey”. Retrieved from https://www.census.gov/programs-surveys/acs/
Demographic changes and urbanization
The US population continues to grow and shift from rural to urban areas. From 2010 to 2030, the US population is expected to increase 15 percent, from 309 million to 355 million, and the percentage living in urban areas is expected to rise from 81 percent in 2010 to 89 percent by 2050.2 This could exacerbate an existing trend—a 160 percent gain in the US urban population since 1980—that has significantly increased VMT in cities.3 Meanwhile, motor vehicles remain the dominant transportation mode.
2, 3 United Nations. (2018). World: Urbanization Prospects 2018 Revision. Retrieved from https://population.un.org/wup/Download/
Transportation disruption: TNC and ride hailing
Ride-hailing has grown, substituting for mass transit, putting more cars on the street, and contributing to congestion at the curb. Transportation Network Companies (TNCs) have experienced explosive growth, from just a handful of trips in 2012 to about 2.6 billion trips in 2017.4 The VMT from these TNCs grew from 30 million in December 2013 to 500 million in December 2016, a compound annual growth rate (CAGR) of 150 percent.5
4, 5 Schaller Consulting. (2018). “The New Automobility: Lyft, Uber and the Future of American Cities”. Retrieved from http://www.schallerconsult.com/rideservices/automobility.pdf
E-commerce and on-demand delivery
Internet-based purchasing is on a rapid growth trajectory, rising in the United States from 0.3 percent of retail spending in 1998 to 8.7 percent in 2014.6 Estimates suggest that this share could rise by as much as 1.2 percent a year through 2030.7 While it once seemed likely that on-demand delivery would prompt consumers to reduce trips to malls and retail stores, the expected drop in VMT never materialized due to the resulting increase in single-package deliveries (and smaller vehicle loads), failed deliveries which drive repeat visits, and the high return rate of e-commerce orders.
6, 7 United States Census Bureau. (2014). Census E-Commerce Statistics (E-STATS). Retrieved from https://www.census.gov/programs-surveys/e-stats.html
Underinvestment in infrastructure
A well run transportation network is critical to limiting congestion, but urbanization has overwhelmed the infrastructure of many cities. This has been particularly problematic in the United States, where roads, bridges, and tunnels already suffer from lack of upgrades and maintenance. The American Society of Civil Engineers’ 2017 infrastructure report card graded U.S. systems a D+ overall. A primary reason for this is the backlog of unmet capital investment needed for highways and bridges: about $836 billion, according to a 2015 US Department of Transportation (DOT) report.
Mixed effectiveness of policies and programs
Cities have embraced a variety of mobility solutions, with mixed effectiveness. For example, high-occupancy vehicle (HOV) and bus-only lanes are supposed to justify their capital-project costs by discouraging the use of private vehicles for commuting, but they often don’t. Because of challenges with enforcement and other operational issues, these solutions tend to lead to more, not less, congestion. Other city parking policies, such as subsidized on-street parking that reinforces the behavior of circling, can also contribute to congestion.