Traffic lights are controlled using a variety of systems, ranging from older electromechanical timers to modern computerized systems. Electrical relays also play a crucial role, particularly in older systems.
Here's a breakdown of the control methods:
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Electromechanical Timers (Older Systems):
- These systems utilize dial timers with fixed time plans for each intersection.
- Cycle lengths (the time it takes for all signal phases to complete) are determined by gears within the dial timer.
- Electrical relays are used to switch the lights according to the preset timing sequence.
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Computerized Systems (Modern Systems):
- These systems use computers to dynamically adjust timing based on real-time traffic conditions.
- Traffic Sensors: Detect vehicle presence and volume using various technologies, including:
- Inductive Loops: Buried in the pavement, these detect changes in magnetic fields caused by vehicles.
- Video Detection: Cameras analyze traffic flow.
- Radar and Lidar: Use radio waves or laser beams to detect vehicles.
- Centralized Control: Data from sensors is sent to a central controller that optimizes timing for the entire network.
- Adaptive Timing: Adjusts signal timing based on the collected data, optimizing traffic flow in real-time.
- Pre-timed control: Signals operate based on a pre-defined schedule, often used during periods of consistent traffic flow.
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Manual Control:
- In emergency situations or during special events, traffic lights can be manually controlled by traffic personnel.
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Emergency Vehicle Preemption:
- Systems allowing emergency vehicles (fire trucks, ambulances, police cars) to change traffic lights to green in their direction of travel.
- Uses devices such as strobe light detectors or GPS-based systems to communicate with traffic signals.
Essentially, traffic light control varies from fixed timing systems using electromechanical relays and timers, to more advanced, adaptive systems relying on sensors and computer algorithms to dynamically optimize traffic flow.
