Ford Transit
'Driverless' Ford Transit was spotted on the streets of Arlington, Virginia Adam Tuss via Twitter

Self-driving vehicles are a regular sight on the roads of California, thanks to Tesla, Google, Uber and others testing their latest technologies. But no matter how advanced the autonomous systems, there is always someone in the driver's seat, ready to grab the wheel.

So it is no wonder that motorists in Arlington, Virginia were alarmed to see a Ford Transit van apparently driving itself with no one inside. Footage published on YouTube shows the vehicle driving through traffic despite its front two seats apparently both being empty.

Some thought the van was from Virginia Tech, which recently received permission to test autonomous technology on public roads. But even that would have required a supervisor in the driver's seat at all times.

On Monday (7 August) the mystery was solved when NBC 4's transportation correspondent Adam Tuss approached the stationary vehicle, to find its driver was wearing a costume disguising him as a seat.

Appearing to drive the vehicle with modified hand controls, the man said nothing before driving off.

Hours later, Virginia Tech came clean and admitted it was using the vehicle as part of an experiment into people's perceptions of driverless vehicles. "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 told NBC in a statement.

The strange experiment comes a year after a Tesla Model S was spotted apparently driving itself on a US highway. By dressing up as the front seat and engaging the car's Autopilot function, YouTube prankster Rahat Hossain then filmed the reactions of other motorists as he covertly drove by.

Both stunts raise interesting questions about the future of autonomous vehicles. It is one thing for cars to temporarily drive themselves while the owner keeps a loose grip on the wheel, but given the reactions to these apparently driver-free vehicles, motorists are, for now at least, not entirely comfortable sharing the roads with truly autonomous cars.

Man disguised as van seat
Virginia Tech researcher is seen disguised as the front seat of a van Adam Tuss via Twitter