A short while ago, residents of Arlington, VA were startled to see a driverless car passing through its streets. At one point a reporter on foot approached the car and looked in and saw that the car did have a driver but that he was disguised as a car seat that he could see through and was controlling the car with his hands held low.

It turns out that this was not just some prank. Designers were studying how to deal with a problem with driverless cars that has not received much attention, and that is their absence of subtle human-to-human communication cues that human drivers use with other users of the road to indicate awareness of their presence and what their intent is. They are seeing whether other means, such as light signals, can be developed as adequate substitutes.

The “seat suit” stunt was the brainchild of Ford and Virginia Tech Transportation Institute research to explore how self-driving vehicles can communicate their intent to pedestrians, human drivers and cyclists.

There are many subtle cues humans use to communicate with each other on the road that disappear when the driver is removed from the equation: eye contact to show a pedestrian they’ve been noticed; a head nod to let another driver take his or her turn at an intersection; or a hand wave of appreciation when changing lanes in heavy traffic.

Ford and Virginia Tech wanted to test how people would react to light signals replacing some of this communication.

“We needed to try out this new lighting to communicate the intent of the vehicle, but if you’ve got a driver behind the seat you still have natural communication between humans like eye-to-eye contact,” said Andy Shaudt, who headed the research at Virginia Tech. “So we needed to make it look like a driverless car.”

Here’s a video that shows the encounters of the car and its light signals with other users.