An artist wheeled 99 smartphones around in a wagon to create fake traffic jams on Google Maps.

At a public May Day gathering in Berlin a few years ago, Simon Weckert noticed something unusual. His Google Maps app showed there was a massive traffic jam, even though there weren’t any cars on the road. After some thought, Weckert realized it was the mass of people in the street—or more specifically their smartphones—that Google Maps was responding to, not actual car traffic. This mass of smartphones had inadvertently tricked Google into seeing gridlock on an empty street. And then he decided to try it himself.

“The question was if it might be possible to generate something like this in a much simpler way,” Weckert says. “I don’t need the people. I just need their smartphones.”

Borrowing from friends and rental companies, Weckert collected 99 old cellphones and piled them into a little red wagon. He then proceeded to march up and down random streets in Berlin, pulling his phones behind him.

It took about an hour for the results to appear on Google Maps, but sure enough, Weckert says his wagon created a long red line in the app, indicating that traffic had slowed to a crawl—even though there wasn’t any traffic at all. And his Google Maps Hack project was born.

A Google representative told Business Insider that the app determines traffic by continuously pinging smartphones that use location services and by using “contributions from the Google Maps community.”

“We’ve launched the ability to distinguish between cars and motorcycles in several countries including India, Indonesia and Egypt, though we haven’t quite cracked traveling by wagon,” the representative said. 

Weckert said that he simply wanted to draw attention to the blind trust that many people have in tech companies and platforms. But in this age of tactical urbanism and DYI traffic engineering, this little Google trick could also be used by residents who may be fed up with the real traffic situation in their own neighborhoods. Fool drivers into thinking your street is a traffic-nightmare, and they’ll likely find another route.

So now you can add the Google Maps Hack next to the good old Invisible Rope method of traffic-calming. Of course, if commuters would just use the subway instead, traffic-hacking might not be necessary.