The van's windows were darkly tinted and cameras and a light bar were seen behind the windshield.
While investigating the mysterious van, NBC Washington's Adam Tuss, realized a man dressed in a car seat costume was actually behind the wheel of the vehicle.
"I looked out and I said, 'Oh my God, there's a guy in a seat costume,'" Tuss said. "How's that possible? Your brain can't get around it for a second."
Tuss approached the 2017 Ford Transit Connect and knocked on the window, where he saw a man's hands and legs sticking out from underneath the costume.
"Brother, who are you? What are you doing? I'm with the news, dude," Tuss said. "Dude, can you pull over and we can talk for a second?"
The driver didn't respond to Tuss, but the Virginia Tech Transportation Institute later revealed the van and its driver are part of a study about driverless cars.
"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 institute said.
Police and the Virginia Department of Transportation said they were not aware of the vehicle, but Arlington county officials were involved in planning the study.