Semafori

Semafori, or traffic lights, are signaling devices installed at road intersections to regulate the movement of vehicles and pedestrians. They convey when to stop, go, or prepare to stop by means of color-coded lamps and, in many places, accompanying signals for pedestrians.

The standard three-color system uses red to stop, amber (yellow) to warn that the signal is about to change, and green to proceed. Some signals include left-turn or straight-right arrows that provide protected movements. Pedestrian signals typically display Walk and Don't Walk indicators, and many cities also show countdown timers indicating how many seconds remain for a crossing.

The concept dates to the 19th century; the first gas-lit semaphore signal appeared in London in 1868 but was soon abandoned after an explosion. Electric signals emerged in the early 20th century in North America; the modern three-color system was widely adopted during the 1920s and 1930s, with national and regional standards gradually harmonized.

Today, semafori are built with energy-efficient LEDs, and many use sensors, cameras, or loop detectors to adjust timing based on traffic demand. Some systems are connected to central control networks, allowing adaptive signaling. Pedestrian accessibility features, including audible signals and tactile indicators, are increasingly common to aid visually impaired users.

Global practice varies by country, but the red–amber–green sequence is typical in many regions. Semafori remain a core element of urban traffic management, with ongoing advances in automation and vehicle-infrastructure integration.