trafficsignal

A traffic signal, or traffic light, is a signaling device used to control vehicular and pedestrian traffic at road intersections and other locations. It uses lights that cycle through colors to allocate right of way and reduce conflicts, improve safety, and coordinate flow.

A typical traffic signal consists of signal heads with red, yellow, and green lenses, a controller or computer-based timing system, and sensors or detectors to adapt to traffic conditions. Pedestrian signals may accompany the vehicular lights, using 'Walk' and 'Don't Walk' indications with countdown timers in many places.

Color meanings and turning signals vary by jurisdiction. In most systems, red means stop, green means go, and yellow signals the imminent change to red, advising drivers to stop or prepare to stop. Protected-turn phases and pedestrian crossing times are programmed to minimize conflicts. Signals may be fixed-time, actuated, or adaptive; actuated signals respond to vehicle presence; adaptive systems adjust cycles based on real-time flow, often via sensors.

Regulatory frameworks govern placement and operation, with examples including MUTCD in the United States and the Vienna Convention in Europe. Proper visibility, mounting height, and power supply are essential. History notes: modern traffic signals emerged in the early 20th century and have evolved with LED lighting, smart controllers, and integration into city traffic management systems.