Traffic lights are structures placed at the intersection of two roads. Using different colored lights, they let drivers know when it is their turn to go across the intersection. Wherever there's an intersection, there's the possibility of an accident if two cars try to cross at the same time. The purpose of a traffic light is to keep wrecks and other traffic accidents from happening by allowing traffic to proceed in an orderly manner, one direction at a time. Signals connected to red lights also indicate when it's safest for pedestrians to cross, reducing the number of people on foot who get hit by cars.
The first traffic light ever built was installed in England in 1868 to direct traffic at the British Houses of Parliament. It was operated by hand by a policeman. Tragically, the newfangled device exploded a little over a year after it was installed, killing the policeman. Today, traffic lights are much improved. The lights change by themselves, and can even be connected to other traffic lights to improve the flow of traffic. The first automated, interconnected set of traffic lights was turned on in Houston in 1922. Fortunately, the newer models are also much less explosive!