Uber and Lyft may be making San Francisco’s traffic worse

It’s no news to San Francisco, California, residents that traffic is getting worse. Now, a new study suggests the biggest culprit, from 2010 to 2016, were cars driving for the ride-sharing companies Uber and Lyft, which are both headquartered in San Francisco. The new findings, based on a computer model that simulated the speed of traffic with Uber and Lyft vehicles removed, echo those of another study of New York City.

A comparison of traffic speeds from 2010, before ride-sharing apps were widely used, with 2016 shows the time cars spent sitting in San Francisco traffic increased by 69%. To find out how much of that was caused by ride-sharing vehicles, researchers used the model to forecast what traffic might have been like in 2016 without Uber or Lyft.

To do this, the authors needed to know how many additional cars Lyft and Uber were putting on the streets. When the companies refused to share this information, researchers used a program that had thousands of “ghost users” ping the Uber and Lyft apps every 5 seconds for 6 weeks in 2016, revealing the locations of nearby drivers—and how many were on the streets at any given time.

The model closely predicted the real-life traffic seen in 2010 and, after plugging in the Uber and Lyft driver data, 2016. The researchers then used the model to envision 2016 traffic minus the cars driving for Uber and Lyft.

Without those cars, the model estimated just a 22% increase in traffic delays from 2010–16, suggesting ride-sharing companies were responsible for more than half of San Francisco’s real-world traffic increase, the authors report today in Science Advances . The remainder of San Francisco’s traffic increase was accounted for by growth in population and employment, which grew by roughly 70,000 people and 150,000 jobs respectively.

Uber and Lyft have long said their services may relieve urban congestion by facilitating access to public transit or even by so overwhelming customers with convenience that they ditch their personal vehicles altogether. Uber did not respond to a request for comment, but a spokesperson for Lyft said the study—which has the potential to affect transportation policy decisions from San Francisco to New York City—does not adequately account for traffic growth because of tourism or delivery services like Amazon.