Last week, motorists in Arlington, Virginia thought they spotted one of the most advanced driverless vehicles ever to hit the roads. Not only was it missing the required co-pilot ready to take control should things go wrong, but it appeared to lack the usual multitude of external sensors found on fully autonomous vehicles.

Video from, which you can see here, shows the van driving around. While the clip looks very convincing, transportation reporter Adam Tuss from NBC's Washington affiliate investigated further. He discovered the vehicle yesterday and peered inside with his camera, only to find that the driver's spot wasn't actually empty - it contained a man dressed in a costume that resembled the front seat.

The hidden driver was controlling the 2017 Ford Transit Connect by holding the bottom of the steering wheel. Tuss tried to speak to the man, but he drove through a red light to get away, making the "driverless car" look like one of the numerous pranks that have appeared on YouTube.

The mystery was finally solved when, following multiple inquiries, Virginia Tech Transportation Institute admitted the van and driver were part of a study it was conducting to see how people reacted to driverless cars. One that would "determine how best to design automated 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 said in a statement.

An institute spokeswoman said county officials were involved in the planning for the study, though a representative for the Arlington Police Department told NBC 4 it was "shocked" by news of the van.