For all the hype surrounding driverless cars, no one knows exactly what their broader implications may be. This week one car designer suggested automated vehicles could deal a setback to trends in the U.S. toward less driving and more sustainable modes.

At the Automated Vehicles Symposium in San Francisco, Ken Laberteaux, senior principal scientist for Toyota’s North American team studying future transportation, spoke with a Bloomberg reporter about the potential for unwelcome outcomes, including more sprawl.

“U.S. history shows that anytime you make driving easier, there seems to be this inexhaustible desire to live further from things,” Laberteaux said. “The pattern we’ve seen for a century is people turn more speed into more travel, rather than maybe saying ‘I’m going to use my reduced travel time by spending more time with my family.’”

He said tolling could be a potential solution, but then went on to question the political practicality of that approach. “We’ve created an entire culture and economy based on the notion that transportation is cheap,” he said.