99 smartphones are transported in a handcart to generate virtual traffic jam in Google Maps.Through this activity, it is possible to turn a green street red which has an impact in the physical world by navigating cars on another route to avoid being stuck in traffic. [...] Google Maps determines congestion by gathering the location and motion speed of phones in a given area. Generally speaking, those phones are going to be in the road because they're with drivers, inside vehicles, and so measuring the phones' speed is a reasonably decent proxy for measuring vehicle speed. Those data points, aggregated, make a road look green on the map if traffic seems to be moving smoothly, or they look red on the map if traffic appears to be severe. When traffic is severe, the map's navigation software will reroute drivers around the congestion when possible.