The devices that control traffic lights and electronic signs in many cities are vulnerable to a number of attacks. Cesar Cerrudo, a researcher and CTO at IOActive, found that the vulnerabilities he identified can be exploited from up to a mile or two away with the right equipment. The vendor he was investigating has deployments of vulnerable systems in several countries, including the United States, China, the U.K., Australia and Canada. The vulnerabilities he found allow anyone to take complete control of the devices and send fake data to traffic control systems.
Source: https://threatpost.com/hacking-traffic-systems-for-fun-and-chaos/105789/