In 2016, Lyft co-founder John Zimmer made the optimist’s case for services like Uber and Lyft in the American city. Zimmer forecast the end of private car ownership in cities within a decade as urbanites abandoned personal cars for the convenience of an increasingly automated and affordable shared fleet of taxis. Street space is repurposed, traffic declines, air quality improves.

That projected deadline is still years away, but the company thinks it’s making good progress. On its annual survey of drivers and passengers, Lyft reports that over 250,000 passengers gave up their personal vehicle thanks to easily available ride hailing. In an email, a company spokesperson cited a congestion study by the consulting firm Inrix, which showed peak-hour congestion falling by 5 percent in San Francisco from 2016 to 2017—a time when Lyft ridership grew 49 percent.

A new report from Bruce Schaller, a consultant and former traffic official in New York City, makes the opposite case. In nine of the country’s major cities (including its three biggest), Schaller argues, about 60 percent of Uber or Lyft rides are replacing journeys that would have been made on transit, on bike, or on foot—or not at all. In other words, ride hailing is mostly a substitute for transit and other transportation alternatives, not a complement. Because users are choosing the car ride instead of the subway and drivers spend a lot of time driving around without passengers (deadheading), Schaller projects services like Lyft and Uber put 2.8 new vehicle miles on the road for every mile of personal car travel they remove.

In short, the report argues that Uber and Lyft are creating a ton of traffic—5.7 billion miles a year in the nine cities he studies. Schaller, who is sympathetic to the cab companies that the startups displaced, has been making this point for some time. As have others. In 2015, New York City Mayor Bill de Blasio tried, and quickly failed, to put a limit on the number of Ubers in Manhattan. But times have changed since then. General Motors is launching a car-sharing service, like an Airbnb for cars. Uber and Lyft, in the meantime, have each purchased a company that rents bicycles—a move that relieves each company’s dependence on the personal automobile.

Uber spokesman Matthew Wing argued that while Uber may well be replacing transit trips, that says more about the quality of the transit that U.S. cities provide: “Yes, when a better option comes along in areas with bad transit, it should not be a surprise that they decide to take that better option.” In Los Angeles, UCLA researcher Anne Brown found that users in low-income neighborhoods made the most Lyft trips per person, and that the presence of carless households is positively correlated with trips. (Schaller also finds that Uber and Lyft usage is higher in cities with a greater share of transit riders.)

More, faster trips are a good thing. That means more people spending less time to commute, to socialize, to run errands, etc. But it poses an intractable problem for cities that only have so much street space. Unfortunately, politicians are already citing Uber, Lyft, and the supposedly imminent arrival of autonomous vehicles to reject transit improvements that could more efficiently move people around. Meanwhile, self-styled climate-warrior mayors refuse to challenge the dominance of personal cars, which still account for the lion’s share of traffic and emissions. All the while, worsening congestion slows ambulances, buses, and freight deliveries while punishing pedestrians, cyclists, and low-income residents with toxic air.

The long-term solution to this problem is a tax that accurately prices the externalities associated with driving alone, which can be funneled to fund better transit. (Not coincidentally, Uber has thrown $1 million behind such a proposal in New York City.)

The short-term solution might lie in the scooters and bicycles that have taken Silicon Valley by storm. If ride hailing is eating transit trips, dockless scooters and bikes (particularly electric ones) appear to be eating ride hail trips. Uber users in San Francisco who started to access the company’s new Jump e-bikes took 15 percent more trips through the app—but 10 percent fewer car rides.

What’s stopping Uber from shifting more trips from cars to bikes? Reactionary urban policy. There’s no limit on how many cars the company can drive into San Francisco—but the city only allows the company to operate 250 bikes, and has banned electric scooters altogether.