The Uber ride-hailing app. (Andrew Caballero-Reynolds/AFP/Getty Images)

About 1 in 15 miles driven in the District is in an Uber or Lyft vehicle, according to a study that offers long-sought details of the services’ impact on traffic in urban areas.

Supporters of the ride-hailing apps have long billed them as a way to ease traffic woes by encouraging people to give up their personal vehicles or leave them parked. But company data released this week demonstrate how the firms represent a significant part of the traffic mix.

Company officials emphasized that their operations represent just a fraction of overall driving in the Washington region and the other cities that were part of the study, which was conducted by the transportation firm Fehr & Peers and funded by Uber and Lyft. The study also looked at Boston, Chicago, Los Angeles, San Francisco and Seattle.

Uber and Lyft “are likely contributing to an increase in congestion,” Chris Pangilinan, Uber’s head of global policy for public transportation, said in a statement. But, he added, “its scale is dwarfed by that of private cars and commercial traffic.”

The data show that about 7 percent of the “vehicle miles traveled” in the District are in Ubers and Lyfts, and the other 93 percent are other cars and trucks. That 7 percent includes time the company drivers spend circling while they wait for a fare or driving to pick up passengers. The companies’ share of the vehicle miles traveled for the entire Washington region was about 2 percent, according to the study.

“I’m delighted to finally see these numbers. They’re something we’ve been trying to get our hands on,” said Paul Lewis, vice president of policy at the Washington-based Eno Center for Transportation.

Lewis noted that the figures are for September 2018, and they do not include data on when trips were taken, which can obscure critical parts of the picture. “D.C. streets aren’t always congested, right?” Lewis said, adding that data showing the amount of miles driven by Uber and Lyft vehicles “during the peak hour is almost more important.”

The data from September 2018 was selected, researchers said, because September is a representative non-summer month with little holiday activity.

Still, the numbers raise important policy questions, Lewis said, about how the firms are drawing riders from transit and about the efficiency of the services, which are posting big losses as they subsidize rides to compete with each other.

“People are leaving the bus and train networks not only because” Uber and Lyft “are cheap but because the transit service they’re providing is not that great,” Lewis said, adding that levies on the ride-hailing services can be directed at improving traffic flow for other city residents through initiatives such as express bus lanes.

Jeff Marootian, director of the District Department of Transportation, said the study “highlights the importance of our efforts to innovate using data and technology to reduce congestion and improve safety at the curbside.” The city has taken steps to “create dedicated pickup and drop off areas for ride-hailing vehicles,” he said, and embraced scooter and bike-share efforts, among other initiatives.

The data show that of the Uber and Lyft miles driven in the District, 19 percent are downtown and 81 percent are in the rest of the city.