Traffic lights have become a standard and effective method for managing vehicle flow on roads today. However, the concept of traffic signals dates back to the 19th century. In 1858, the first traffic light was installed in London, England, using gas-powered red and blue mechanical signal lamps to control carriages. This marked the beginning of modern traffic management. A few years later, in 1868, engineer Nathan Smith designed the world’s first gas-powered traffic light, which was placed in front of the Parliament Building in Westminster. It featured a rotating lantern with red and green lights, where red meant “stop†and green indicated “caution.†Unfortunately, this system had a major flaw—on January 2, 1869, the gas lamp exploded, injuring a police officer and leading to its immediate removal.
Today, urban traffic control systems are advanced computer-based solutions that monitor traffic data, manage signal timing, and provide real-time guidance. These systems play a crucial role in modern city infrastructure. The challenge lies in using current technologies such as computers and automation to optimize traffic flow, increase intersection capacity, improve vehicle speed, and reduce accidents. In this paper, we explore the design of an urban and rural traffic light control system based on PLC (Programmable Logic Controller), focusing on both theoretical calculations and practical testing.
The system is designed to control traffic lights at intersections, with red, yellow, and green lights operating in a specific sequence. When the start switch is activated, the system begins by turning on the north-south red light while the east-west green light is active. After 25 seconds, the north-south green light turns on, followed by a 20-second countdown. At the end of this period, the green light flashes for 3 seconds before turning off. Then, the east-west yellow light activates for 2 seconds, after which the east-west red light turns on. Simultaneously, the north-south green light turns off, and the north-south red light comes on again, repeating the cycle continuously.
The hardware setup uses a Siemens S7-200-224 PLC as the central controller. Input devices include a start button (SB1) connected to I0.0, while output relays control the red, yellow, and green lights for both directions. The wiring diagram is shown in Figure 1, illustrating how each component is connected to the PLC. The ladder logic design follows a sequential control approach, dividing the operation into steps that transition based on time and conditions. This ensures that the system operates smoothly and reliably, with clear logical relationships between input signals and output actions.
Figure 2 presents the ladder diagram of the traffic light control system. When the PLC is powered on, it starts in the initial state (S0.0). Pressing the start button (SB1) initiates the sequence, activating the east-west green light and starting a 20-second timer. After the timer completes, the green light begins flashing, followed by the activation of the yellow light for 2 seconds. Then, the red light turns on, and the cycle repeats. The same process applies to the north-south direction, ensuring coordinated operation between both directions.
In conclusion, implementing a traffic light control system requires careful planning and reliable technology. Traditional methods often lack the stability and efficiency needed for high-traffic areas. PLC-based systems offer significant advantages, including ease of use, flexibility, and reliability. The design presented here meets all functional requirements and demonstrates the potential for real-world application. With further development, such systems can contribute to safer and more efficient urban transportation networks.
For those interested in exploring more, there are various resources available, including free downloads of PLC traffic light circuit designs, course projects on FPGA-based traffic light controllers, and microcontroller-based traffic light control systems. Each offers unique insights into different approaches to modern traffic management.
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