UK Research Demonstrates TNCs a Major Contributor to Roadway Congestion in San Francisco

The San Francisco County Transportation Authority has released “TNCs and Congestion,” a report providing the first comprehensive analysis of how Transportation Network Companies (TNCs) Uber and Lyft collectively have affected roadway congestion in San Francisco. The report found that Transportation Network Companies accounted for approximately 50 percent of the rise in congestion in San Francisco between 2010 and 2016, as indicated by three congestion measures: vehicle hours of delay, vehicle miles traveled, and average speeds. Employment and population growth were primarily responsible for the remainder of the worsening congestion.

The Transportation Authority partnered with experts from the University of Kentucky to conduct the research. Greg Erhardt, an assistant professor, led the research team that conducted the analysis and drafted the findings. He was joined by Mei Chen, an associate professor, and Sneha Roy, a Ph.D. candidate.  All three are part of the transportation engineering and data science program in the Department of Civil Engineering. 

The report utilizes INRIX data, a commercial dataset which combines several real-time GPS monitoring sources with data from highway performance monitoring systems and a unique TNC trip dataset provided to the Transportation Authority by researchers from Northeastern University. These data are augmented with information on network changes, population changes, and employment changes provided by local and regional planning agencies, which are used as input to the Transportation Authority’s activity-based regional travel demand model SF-CHAMP.

Major findings of the TNCs and Congestion report show that collectively the ride-hail services accounted for:

• 51 percent of the increase in daily vehicle hours of delay between 2010 and 2016;
• 47 percent of the increase in vehicle miles travelled during that same time period; and
• 55 percent of the average speed decline on roadways during that same time period.

On an absolute basis, the Transportation Authority estimates that TNCs comprise 25 percent of total vehicle congestion (as measured by vehicle hours of delay) citywide and 36 percent of delay in the downtown core. Notably, the report indicates that TNC activity affects congestion differently throughout the day and throughout the city. TNCs caused increased congestion across all times of day, including the morning peak, midday and evening peak, but the increase attributable to TNCs was most pronounced in the evening.

Consistent with prior findings from the Transportation Authority’s 2017 TNCs Today report, TNCs also caused the greatest increases in congestion in the densest parts of the city - up to 73 percent in the downtown financial district - and along many of the city’s busiest corridors.

Tilly Chang, Executive Director of the San Francisco County Transportation Authority, said: “Understanding the drivers of congestion is key to our ability to address the problem effectively and maintain the accessibility of our downtown core. We are committed to data-driven analyses like this report to serve as the foundation for deeper understanding and informed action.”

The TNCs and Congestion report uses the following common measures of roadway congestion:

• Vehicle Hours of Delay: Measuring the overall amount of excess time spent in congestion, it is the difference between congested travel times and free flow travel times on a given roadway segment.
• Vehicle Miles Traveled: A measure of the overall amount of travel, as measured in distance, that occurs on the streets.
• Speed: The average speeds on streets.

 The full report, downloadable data files, and an interactive map are available at sfcta.org/tncsandcongestion.

Eric Young, San Francisco County Transportation Authority, and Kel Hahn, UK College of Engineering contributed to this article.