The man in the seat-cushion costume got all the attention. What appeared to be a driverless vehicle actually had a researcher sitting in the front seat, disguised to make it look like he wasn't behind the wheel.
But the strip of white lights on the top of the windshield offered a clue to the sort-of-clandestine study Virginia Tech is running on the streets of Arlington County, Virginia.
Take a close look at the video of the van tooling around Arlington captured by the news site ARLnow, which, with an assist from NBC Washington's Adam Tuss, unmasked the presence of the rolling experiment.
Tuss knocked on the van's window when he saw it Monday, but the guy in the costume declined to answer questions.
"We're trying not to dirty the data and make sure people aren't keeping their eyes peeled," said Mindy Buchanan-King, a spokeswoman for the Virginia Tech Transportation Institute.
The video shows the white strip of windshield lights flickering more or less around crosswalks.
So what's going on?
Researchers are working to make sure their robocars can emit some kind of replacement for the subtle cues that drivers and pedestrians rely on to stay safe.
Developers have taught driverless cars to stay in their lanes, steer around obstacles and follow traffic laws. More and more passengers are being ferried around in test vehicles and getting comfortable giving up the wheel. Now there's a focus is on "external communication."
"It's basically the next big topic we need to tackle," said Myra Blanco, a senior autonomous vehicle researcher at Virginia Tech. From eye contact to little waves, communication between humans is a vital part of what happens on the roads, she said.
When a pedestrian is ready to cross the street, "there's usually that looking at the driver. Is he going to let me go? Should I wait? Is he paying attention or not?" Blanco said.
Same thing with cars at an intersection. "If you have a stop sign, are you going or am I going? Okay, you go ahead first. You kind of do a wave."
Blanco declined to answer questions about the research with the silver van, because she doesn't want to foul up work being conducted by colleagues.
Buchanan-King would not say whether the costumed researcher in the front seat was there as backup, as is customary in driverless testing, or was driving himself.
Virginia Tech released a statement saying "the driver's seating area is configured to make the driver less visible within the vehicle, while still allowing him or her the ability to safely monitor and respond to surroundings."
The study "is investigating the potential need for additional exterior signals on automated vehicles. This research is relevant for ensuring pedestrians, cyclists, and other drivers are accommodated," according to the statement.
It will eventually be made public.
But researchers from Virginia Tech, Ford Motor Company, the University of Leeds and Japan's National Institute of Advanced Industrial Science and Technology outlined more details about the questions being considered in such research at symposium this summer.
Among them: How should cars communicate with others on the road while they're moving, stopped or transitioning? And would it make sense to standardise such communication?
In addition to eye contact and gestures, people on the road communicate with "turn signals, horns, and even the control of their movement to show intent (e.g. easing vehicle forward)," according to a summary of the researchers' discussion at the Automated Vehicles Symposium held in San Francisco last month.
It's unclear whether driverless cars "will be able to perceive and communicate intent in the same ways that a human can," according to the summary, so designing them "to signal their intent in ways other roadway users can reliably understand" is critical.
Buchanan-King said the Arlington van was taken off the road temporarily to check in with the driver, given all the attention. "He was fine," she said. "As far as I know the study will continue as planned."
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