At major city intersections, conflicting streams of vehicles, bicycles and pedestrians require precise coordination to move safely and efficiently. Traffic signals provide a standardized method for assigning right-of-way, balancing cost, space constraints and safety needs. Each intersection typically manages eight vehicle movements and four pedestrian phases, organized into timed sequences that allow specific directions to proceed while others wait. Engineers design these phases using ring-and-barrier diagrams to minimize conflicts, often grouping left turns from opposite approaches to share a signal phase. The duration of each signal phase depends on traffic demand, with longer green periods used during peak congestion to clear queues, and amber intervals timed to allow safe deceleration based on speed limits and road conditions. Simple fixed-timing systems are increasingly supplemented with actuated controls that use road-surface loop detectors or radar to sense vehicle presence and adjust signals in real time. These systems can extend green lights when traffic builds up, shorten them when no vehicles are waiting, and prioritize emergency vehicles through specialized sensors. However, isolated signals cannot fully optimize flow across entire corridors. Coordinated signal networks address this by synchronizing multiple lights along major roads, enabling platoons of vehicles to travel through successive intersections without stopping. More advanced adaptive systems collect data from numerous detectors to apply algorithmic optimization across entire urban networks, though they remain limited in deployment due to cost and cybersecurity concerns. While future technologies like vehicle-to-vehicle communication may eventually reduce reliance on physical signals, current infrastructure continues to evolve as cities seek to improve capacity and safety within existing urban layouts.