What will happen when driverless cars are increasingly taking to the roads, but human drivers are still operating, say, half of the cars out there? Some researchers believe safety will actually worsen during this time—at least for the people in cars driven by humans. This isn’t just because humans are worse drivers than computers—and, certainly, they are—but because humans will be forced to navigate a vehicular environment that lacks many of the cues we use now to get around.

“In many current situations, interacting drivers of conventional vehicles make eye contact and proceed according to the feedback received from other drivers,” wrote Michael Sivak and Brandon Schoettle, transportation researchers at the University of Michigan, in an essay for Time last month. “Such feedback would be absent in interactions with self-driving vehicles.”

And even if people become accustomed to interacting with cars without human drivers, they’ll have to form different expectations based on which kind of driverless car they’re encountering. “Given that all vehicles may not be programmed the same way, drivers might not know what to expect from a self-driving vehicle from one manufacturer versus another,” wrote Sivak and Schoettle.