Sinal de trânsito
Complexo esquema de semáforos, na Alemanha
Semáforo de LED com contador regressivo, Poá-SP, Brasil.
Semáforo (também conhecido popularmente como sinal, sinaleira e farol) é um instrumento utilizado para controlar o tráfego de veículos e de pedestre (português brasileiro) ou peão (português europeu) nas grandes cidades em quase todo o mundo. Utiliza uma linguagem simples e por isso de fácil assimilação. É composto geralmente por três círculos de luzes coloridas:
Traffic lights, also known as traffic signals, stop lights, stoplight, traffic lamps, stop-and-go lights, robots or semaphore, are signaling 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 to control the flow of traffic. They assign the right of way to road users by the use of lights in standard colors (Red - Amber - Green), using a universal color code (and a precise sequence, for those who are color blind). They are used at busy intersections to more evenly apportion delay to the various users.
The most common traffic lights consist of a set of three lights: red, yellow (officially amber), and green. When illuminated, the red light indicates for vehicles facing the light to stop; the amber indicates caution, either because lights are about to turn green or because lights are about to turn red; and the green light to proceed, if it is safe to do so.
There are many variations in the use and legislation of traffic lights, depending on the customs of a country and the special needs of a particular intersection. There may, for example, be special lights for pedestrians, bicycles, buses, trams, etc; light sequences may differ; and there may be special rules, or sets of lights, for traffic turning in a particular direction. Complex intersections may use any combination of these.
Traffic light technology is constantly evolving with the aims of improving reliability, visibility, and efficiency of traffic flow.