Traffic lights adjust automatically to traffic in many modern cities, but not all traffic systems are this advanced yet. The main reasons for this are a mix of technical limitations, infrastructure costs, and the complexity of real-time traffic management.

1. Smart Traffic Systems Exist: Advanced traffic systems, often referred to as “adaptive” or “smart” traffic control, do exist and use sensors, cameras, and AI to adjust signal timing based on real-time traffic flow. For instance, if one road is more congested, the system can extend the green light to alleviate the traffic. These systems can improve traffic flow and reduce congestion, especially in high-density urban areas.
2. High Costs and Infrastructure Needs: Implementing such systems requires significant investment in infrastructure, including installing sensors, cameras, communication systems, and central control software. Upgrading existing traffic light systems to smart systems can be costly, and not all municipalities have the budget for these upgrades.
3. Legacy Systems: Many traffic lights still operate on fixed timing schedules, which are based on historical traffic patterns rather than real-time conditions. These systems are less expensive to maintain and have been in place for decades, so upgrading them often occurs slowly and incrementally.
4. Data and Complexity: Real-time traffic management requires processing a vast amount of data and coordinating traffic flow across a network of intersections. This can be technically complex, especially in large cities with unpredictable traffic patterns. Traffic engineers often design the systems for a balance between automation and manual control to handle exceptional events like road closures, accidents, or unexpected congestion.
5. Inconsistent Deployment: Even in cities with smart traffic lights, deployment can be inconsistent. Some intersections may be equipped with adaptive systems, while others may still operate on fixed schedules, leading to uneven traffic experiences.

While adaptive traffic systems are becoming more common, widespread adoption takes time due to these challenges.