Simplify the following text for a Grade 8 native English-speaking person.
Original: Traffic lights , which may also be known as stoplights , traffic lamps , traffic signals , stop-and-go lights , robots or semaphore , are signalling devices positioned at road intersections , pedestrian crossings and other locations to control competing flows of traffic . Traffic lights have been installed in most cities around the world .
Simplified: Traffic signals are instruments for controlling traffic by using changing lights .