Americans badly need more convenient public transport, but the risks of privatization are grave. Last year, Uber logged some five billion trips and $1.8 billion in losses; Lyft provided 619 million rides and reported more than $900 million in losses. These apps are popular because they’re artificially cheap: Uber and Lyft subsidize rides to increase their number of monthly users, a key metric for investors, while allocating relatively little per trip to drivers.

But by reducing the cost of individual rides, Uber and Lyft also draw a privileged subset of passengers away from public transit systems. That, in turn, undermines support for public transportation.

Researchers have also found that ride-hailing tends to make cities more congested and polluted, not less. Alejandro Henao of the National Renewable Energy Laboratory, who drove for Uber and Lyft as part of his research, showed that in Denver, ride-hailing was responsible for an 83 percent increase in the miles that would otherwise have been traveled by car. Much of that increase came from “deadheading,” or driving in search of the next fare. As Mr. Henao puts it, Uber may be reducing the public-transit base without providing enough services “to make up for that negative effect.”

Then there’s the question of accountability. “With public agencies, there’s a protocol for how to hold them responsible, whereas with private companies, their bottom line is profit,” said Naomi Iwasaki, a transportation planner and advocate in Los Angeles. “They look at their users as customers, not constituents.”

Ride-hailing companies “make a lot of money off these streets and sidewalks,” she noted, but they have no obligation to invest in the infrastructure they use. Nor are they required to serve low-income neighborhoods or cater to the elderly, non-English speakers or people with disabilities.

All of this erodes the fundamental idea of public transportation as a service that everyone uses. Jarrett Walker, a transit-design consultant, recently noted on the “Rideshare Guy” podcast that when Uber and Lyft divert relatively affluent riders from public transit, there’s a damaging effect on “elite opinion.” He added: “The notion among elites that, ‘Well, Uber is the thing, because it’s so convenient to me. Therefore, public transit should somehow become more like Uber.’”

As the stereotype goes, the public sector is bloated and inefficient; the private sector, lean and ruthlessly productive. And yet Uber and Lyft, billions of dollars in the red, have set their sights on community transit — not because they can do it better but because they need to be bailed out.

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