Years of emerging research has yielded a murky mix of answers to those questions since Uber hit the road in 2009. At various points, the main ride-hailing companies have alternated between actively promoting their services as weapons that destroy public transit and positioning them as something more like partners that help people access other modes. But a new working paper by U.C. Davis transportation researchers—which reflects perhaps the most comprehensive survey of ride-hailing use in U.S. cities—makes some clear indications: The likes of Uber and Lyft are adding car trips to city and suburban streets, and in many cases, cannibalizing transit.