The two went beyond road building to show that increases in public transit and changes in land use — basically, building apartments next to office buildings so that more people can walk or bike to work — also fail to cut traffic (or do so only a little).

This doesn’t mean public transit and land planning are bad ideas, or that widening freeways is a bad idea. When roads are bigger, more people can get around. More people see family; more packages are delivered; more babies are lulled to sleep. It just means that none of those measures have done much to reduce commute times, and self-driving cars seem unlikely to either.

That’s where charging people during busy times comes in. “Maybe autonomous cars will be different from other capacity expansions,” Mr. Turner said. “But of the things we have observed so far, the only thing that really drives down travel times is pricing.”

This is because the average person prefers the privacy and convenience of riding in a car. Only when the drive is far enough or the traffic is bad enough — or a taxi costs enough — will more people choose to bike, car-pool, hop on a train or postpone a trip. This same pattern shows up in all kinds of places. You can see it in car-centric cities like Los Angeles and Houston, where yearslong, multibillion dollar lane-widening projects did little to speed commutes.

But you can also see it in New York — by far the most transit-friendly city in the United States. Ride-hailing services like Lyft and Uber have led to increased auto traffic, according to a February study from Schaller Consulting in Brooklyn, while subway trips dipped slightly in 2016 because of a fall in weekend usage.

Bruce Schaller, principal of Schaller Consulting, said if the growth in ride-hailing services continued, it would inevitably push the city toward some sort of congestion pricing system, an idea New York has floated and rejected.

“There will be so many cars on the streets, and freight deliveries and buses and everyone else will be so slowed down, that people will get fed up and demand a solution,” he said. “And we have a solution in pricing.”