For all the tensions that Uber and Lyft have had with taxicabs, the bigger questions about ride-hailing companies have to do with their effects on all the other ways you might get around.

Have they siphoned riders from public transit, or have they made transit feasible for more riders?

Have they enabled people to ditch their cars, or only encouraged people to use cars (driven by other people) even more?

The answers will determine how chaotic our streets become. And they could tell us something about how people will behave in a more far-off future of self-driving cars, when ubiquitous ride-hailing will have no one at the wheel.

The answers are still up for debate because these services remain relatively new, because the companies that offer them guard their data, and because even they don’t track the counterfactuals. There’s no button in the Uber app that asks, “If Uber weren’t an option, how would you get where you’re going?”