Far from reducing traffic, the ride-sharing companies were the biggest contributors to its growth as commuters ditched bus rides or walking for the convenience of their mobile-app summoned rides. (Shutterstock/Andrew Zarivny)
One of the early promises of the ride-hailing era ushered in by Uber and Lyft was that the new entrants would complement public transit, reduce car ownership, and help alleviate urban congestion.
But a new study on tech hub San Francisco published Wednesday in Science Advances has found the opposite may be in fact be true: far from reducing traffic, the companies were the biggest contributors to its growth as commuters ditched bus rides or walking for the convenience of their mobile-app summoned rides.
The peer-reviewed paper, which adds to a growing body of research in the area, was co-authored by scientists at the University of Kentucky and a team at the San Francisco County Transportation Authority (SFCTA).
It used 2010, when so-called transportation network companies (TNCs) didn't exist, as its baseline to compare travel times and roadway conditions to 2016, when they were firmly established.
But the period also saw the city's population grow from 805,000 to 876,000, while some 150,000 jobs were added to the economy and numerous changes made to the road network.
In order to account for these developments, the authors used a computer model to establish a counterfactual: what would things look like if ride-hailing companies had not hit the scene?
Greg Erhardt, an assistant professor in engineering at the University of Kentucky, told AFP that the team had indeed found "some substitution" from private cars to TNCs as well as a slight increase in carpooling.
"But the net effect is that two-thirds of TNCs are new cars added to the roadway, that would otherwise not be present."
The team also found that weekday vehicle hours of delay -- defined as the difference in travel time in congested versus free-flow conditions -- increased by 62 percent and that average speeds decreased by 13 percent between 2010 and 2016.
By contrast, in the simulated model without ride-hailing companies, weekday vehicle hours of delay increased by only 22 percent and average speeds decreased by just four percent.
Deadheading, pickups and drop-offs
The findings were challenged by Lyft, which said the study had failed to account for increased freight and commercial deliveries -- an area where Amazon and others have aggressively expanded in recent years, as well as tourism growth.
"Lyft is actively working with cities on solutions backed by years of economic and engineering research, such as comprehensive congestion pricing and proven infrastructure investment," the company said in a statement noting its investments in shared rides and bikes.
Uber likewise said: "While studies disagree on causes for congestion, almost everyone agrees on the solution," adding it too backed proposals for congestion charges.
The study comes as rideshare drivers in major US cities were set to stage a series of strikes ahead of Uber's keenly anticipated Wall Street debut. Lyft went public in March.
Proponents of ridesharing often cite the argument that the majority of rides take place at non-peak times, such as when people have gone for a night out and are returning home from bars.
But the study found peaks occurring at 7:00 am and 8:00 am and then again around 5:00 pm and 6:00 pm.
Among the cars' most disruptive activities on traffic flow was curbside pickups and drop-offs, especially on major arterial roads, it found.
Another notable effect was so-called "deadheading," which Erhardt explained as driving around in search of the next customer. "It doesn't serve a purpose in terms of transporting a person. So that's purely an addition to traffic."
The study relied on background traffic speed from GPS data obtained from a commercial vendor, but when the researchers approached the companies to share their own trip data, they were denied access.
They were forced then to rely on a method of data scraping developed by Northeastern University that uses the companies' public apps to learn about vehicle movements.
Elliot Martin, a research engineer at the University of California Berkeley's Transportation Sustainability Research Center, who was not connected to the study, said its methodology was rigorous.
"I think that they did a good job of trying to draw comparisons, to look at what would have happened in a world where TNCs didn't exist versus where they did exist," he said, adding the methodology was the "best available" given the amount of information.
Despite the findings, ride-hailing isn't all bad, said co-author Joe Castiglione of the SFCTA.
"They are providing services like helping people move around in the evening when transit isn't great, or assisting the visually impaired," he told AFP.
The trick, he said, was to determine "how do we manage the positive benefits without the negative externalities" through new policies like congestion pricing or curbside drop off regulation.