Ride-sharing services like Uber and Lyft have become popular by offering a convenient alternative to crowded public transportation and stressful city driving. But a new study conducted in San Francisco adds to a growing body of evidence suggesting that the services come with a significant downside: increased traffic congestion.

The study showed that San Franciscans spent 62 percent more time sitting in traffic in 2016 than in 2010, before ride-sharing went mainstream. The researchers behind the study, a joint effort of the San Francisco County Transportation Authority and the University of Kentucky, found that ride-share cars were responsible for more than half of the increase.

“It’s simply a matter of too many cars on a road at a particular point in time,” said study co-author Greg Erhardt, assistant professor of civil engineering at the university. Given the companies’ claims that they help ease traffic congestion, he added, the new finding shows the importance of “understanding that there are trade-offs and understanding not to believe the hype without questioning it.”

The study, published Wednesday in the journal Science Advances, isn’t the first research to suggest that ride-sharing apps are making urban traffic worse. A 2018 report found that Uber, Lyft and other ride-sharing services are contributing to congestion in Boston, Chicago, Los Angeles, Miami, New York, Philadelphia, Seattle, and Washington, as well as San Francisco.

The San Francisco County Transportation Authority began the research after noticing that the rise of ride-sharing seemed to coincide with a noticeable spike in traffic congestion in the city. “People were saying, ‘It feels like there’s a lot more congestion,’” said Joe Castiglione, the authority's deputy director and a co-author of the study. “Is there a relationship between these two things?”

To answer that question, the researchers tracked ride-share pickups and drop-offs in San Francisco during a six-week period in 2016. They found that most occurred in parts of the city that already were highly congested and at times when traffic was at its worst, concluding that rather than taking cars off the road, ride-share apps were aggravating rush-hour gridlock in downtown San Francisco.

After finding that traffic levels in San Francisco had increased sharply from 2010 to 2016, researchers used a computer simulation to show how traffic would have changed over the same six-year period in the absence of ride-sharing and found that traffic rose only 22 percent in the “counterfactual” model.

In other words, San Francisco was more congested with ride-sharing than it would have been without.

"These results lead us to conclude that transportation network companies are the biggest factor driving the rapid growth of congestion and deterioration of travel time reliability in San Francisco,” the researchers wrote. “These findings are of interest to transportation planners, to policy makers and to the general public in San Francisco and other large cities.”

Erhardt and Castiglione acknowledged the limitations of the methodology, including its inability to account for some factors that might have influenced congestion, like increased truck traffic due to the popularity of online shopping. But Erhardt said the study suggested that some people in San Francisco who at one time might have walked or used public transportation to get around might have shifted to ride-sharing instead.

Other experts agreed.

“When the cost of something decreases, people typically (perhaps always) do more of it,” Andrew Owen, a research fellow at the University of Minnesota's Center for Transportation Studies in Minneapolis, who wasn’t involved in the new research, told NBC News MACH in an email.

Owen said there were many strategies that might be used to help ease traffic congestion in San Francisco and elsewhere, including taxing ride-sharing companies and upgrading public transportation. But he said he would continue to use ride-sharing services, adding, “We just need to make sure we’re addressing the cost it imposes on the world around us.”

Uber didn’t respond to a request for comment about the study. Lyft spokesperson Alex Rafter said the company was partnering with cities to find ways to ease congestion. “We’re investing deeply in products and new infrastructure for bikes, transit and shared rides to contribute to the greater solution,” he said in an email.

The new study comes at a busy time for the ride-sharing industry. Uber is scheduled for an $80 billion to $90 billion initial public offering Friday, prompting Uber and Lyft drivers in New York, Los Angeles and other major cities to strike Wednesday morning in protest against low wages and sudden firings by the ride-share giants.

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