In the 1930s, New York building commissioner Robert Moses built one highway and bridge after another, with the aim of relieving congestion in America's biggest city. But each time, the result was the same: worse traffic.

What's going on: Eight decades later, transportation experts are observing a similar phenomenon with the world's newest urban innovation: ride-hailing services. According to a major new study, Uber, Lyft and their smaller rivals are clogging major U.S. cities — not relieving congestion — and even more traffic may be on the way when self-driving cars are commonplace.

On Thursday, the New York City Council began considering bills aimed at capping ride-sharing services. A vote may come as early as August 8, and any cap would be a first for a U.S. city.

Why it matters: A major promise of the self-driving, ride-hailing future has been cleaner, more walkable, and people-friendly cities, with much more efficient, individual transportation. But if the study — like others before it — is accurate, we are instead heading toward a bigger problem.

Bruce Schaller, a former New York deputy commissioner of transportation and author of the report, tells Axios that when people use a ride-hailing company, they are opting to do so rather than take public transportation, walk or bike. They generally are not choosing between hailing and driving themselves.

U.S. ridership is surging, he said — up 37% last year, to 2.6 billion passengers, from 2016.

And hailing added 5.7 billion miles of driving a year to the nine cities in the study compared with six years ago — Boston, Chicago, Los Angeles, Miami, New York, Philadelphia, San Francisco, Seattle and Washington.

Uber and other ride-hailing services may not have exacerbated traffic initially. "But now they are clearly a source of congestion, and to deal with congestion you have to deal with them," he said.

Schaller's report aligns with an October study released by UC Davis. It found that, in U.S. cities, 49% to 61% of ride-hailing trips would have not been made at all — or by walking, biking, or public transit.

Regina Clewlow, a transportation research scientist and an author of the UC Davis study, told Axios that no one expected such consumer demand for the rides.

"Cities were blindsided by the dramatic growth of ride-sharing companies," she said.

Clewlow urged continued investment in public transportation. "There’s no way that ride hailing could move people around as efficiently as mass transit."

This outcome also repeats history. In his classic biography of Moses, The Power Broker, Robert Caro described the phenomenon as "traffic generation."

"The more highways were built to alleviate congestion, the more automobiles would pour onto them and congest them and thus force the building of more highways — which would generate more traffic and become congested in their turn in an inexorably widening spiral that contained the most awesome implications for the future of New York and of all urban areas."

— Robert Caro

Schaller disputed a broad consensus among mobility experts that autonomous cars will relieve urban congestion. He said that, instead, self-driving vehicles will create the same dynamic as seen today with ride-hailing. And to the degree the cities become more congested, people will increasingly avoid them, he said.