Every day we travel on city roads, traffic signals are an all-too-familiar presence. It seems simple, but it plays a key role in maintaining traffic order and ensuring travel safety. In this article, we will explore the working principle of traffic signals, bring you to unravel the mystery behind it, and enhance traffic safety awareness.
Traffic lights
The green signal is a clear indication of passage. Whether a driver is eager to continue his journey or a pedestrian is waiting to cross the street, the sight of green means it is safe to proceed. During off-peak hours in many cities, Intelligent Transportation Systems (ITS) come into play to synchronize signals at multiple intersections, creating a “green band”. Vehicles can continuously pass through multiple green-light intersections, which not only reduces stopping and waiting time, but also reduces fuel consumption, effectively eases traffic congestion, and makes road traffic smoother and more efficient.
Red is the most eye-catching color in traffic signals, which represents immediate stop. When the red light is on, vehicles and pedestrians must stop and wait patiently, leaving space for traffic from other directions. This uniform rule greatly reduces the likelihood of intersection collisions and makes traffic flow predictable. At the same time, red lights also provide a buffer for drivers, reminding them to maintain a safe distance when approaching an intersection, thus protecting pedestrians, non-motorized vehicles and other motor vehicles in all aspects and building a solid foundation for road safety.
The yellow signal, which sits between the red and green colors, serves as both a warning and a buffer. It acts as a reminder to all road users that the signal is about to change. For vehicles that are too close to the stop line to brake immediately, the yellow light provides valuable reaction time to avoid accidents such as rear-end collisions caused by harsh braking. Despite their short duration, yellow lights play an indispensable role in ensuring an orderly transition of traffic.
While red, yellow and green are standard for traffic signals in most parts of the world, in some places white signals play a special role. White signals are often used to manage special bus lanes, such as Bus Rapid Transit (BRT) systems. These white signals, usually in the form of horizontal or vertical bars, provide BRT drivers with the instructions to proceed, yield, or stop, distinguishing between regular vehicles and public transportation, and allowing public transportation to operate efficiently without interfering with the flow of regular traffic.
Traffic signals lights generally follow a fixed timed cycle of operation. The red, yellow and green lights come on for pre-determined periods of time. These timings are not arbitrary, but take into account a number of factors, such as the size of the traffic flow, the size of the intersection and the overall traffic conditions. In busy intersections, in order to allow more vehicles to pass smoothly, the green light will be lit for a longer period of time; while in smaller traffic flow, the green light will be shortened to ensure that vehicles in all directions can pass fairly, avoiding too long a wait.
Traffic lights
In urban traffic management, signal coordination is crucial. Many cities will synchronize the control of signals on major roads so that when a signal at an intersection turns green, subsequent signals along that route will also turn green in sequence, forming a “green band”. The advantages of this system are significant, as vehicles can continuously pass through multiple green-light intersections, reducing frequent stop-start situations, effectively reducing the level of congestion, shortening travel time, and providing drivers with a smoother driving experience.
Traffic signals are mainly classified into two types: timed and sensor-based, which have their own advantages and disadvantages and are suitable for different traffic scenarios.
| Type | Operation Mode | Advantages | Suitable Scenarios |
| Fixed-Time Traffic Light | Operates on a preset schedule, unaffected by real-time traffic conditions. | Simple system structure with low construction and maintenance costs. | Roads with stable, low-variation traffic flow, such as suburban roads. |
| Actuated Traffic Light | Uses sensors, cameras, or radar to detect vehicles and adjust timing dynamically. | Adapts flexibly to traffic changes, improving overall traffic efficiency. | Urban main roads or commercial intersections with significant traffic fluctuations. |
Accurate detection of the presence of vehicles is the key to efficient management of traffic signals. Currently, the following technologies are used to accomplish this task.
Inductive loops consist of coil wires buried under the roadway. When a vehicle drives through or stops above the coil, the metal parts of the vehicle will cause a change in the magnetic field around the coil, and the system will be able to determine the presence of the vehicle by detecting this change. Depending on the number of vehicles detected, the signal timing can be adjusted accordingly to ensure the efficiency of the intersection, which is particularly suitable for fine-tuning traffic flow management.
Traffic lights
Advanced traffic cameras are like intelligent “eyes” on the road. They capture real-time images of the road and use image recognition and processing technology to detect and track vehicles. By analyzing the captured images, the camera not only counts the number of vehicles, but also identifies traffic patterns and determines the level of congestion. The information obtained in real time provides the basis for the signal light system to adjust the light time in real time, making the traffic management more intelligent and efficient.
Radar sensors utilize radar waves to determine the position and speed of vehicles with high precision. It can accurately obtain the vehicle’s traveling dynamic information, especially suitable for the monitoring of fast-moving vehicles. By analyzing the radar data, traffic signals can be adjusted in time to avoid traffic bottlenecks and ensure the overall efficiency of the road.
There are many types of traffic signals, each of which is designed to meet specific traffic needs and work together to ensure the orderly operation of traffic.
Standard traffic signals are the most common type of traffic signals we see on the road, which consists of three colors of light: red, yellow and green. Both vehicles and pedestrians act according to the instructions of standard traffic signals when passing through intersections. Its eye-catching colors and simple, easy-to-understand rules effectively maintain traffic order and greatly reduce the risk of traffic accidents, making it an important “guardian” of road traffic safety.
Traffic signal lights
Pedestrian traffic signals are specially designed to ensure the safe crossing of streets by pedestrians. It provides clear and unambiguous instructions to pedestrians by signaling both “wait” (usually a red palm icon) and “pass” (a green pedestrian walking icon). At many intersections, pedestrian traffic signals are used in conjunction with standard traffic signals to further enhance the safety of pedestrians crossing the street with confidence.
Turn Arrows are special members of the traffic signal that clearly inform drivers when they can turn left or right by indicating with a separate arrow. This design manages the flow of turning traffic separately from the flow of straight traffic, effectively reducing conflicts between straight and turning traffic, smoothing traffic flow at intersections, and improving overall traffic safety.
Urban and rural traffic conditions are different, and so are the needs for signalization. In urban areas with heavy traffic and many pedestrians, advanced and complex signal systems are needed to handle complex traffic conditions, while in rural areas with low traffic volumes, simple signal designs can meet basic traffic management needs. Adapting the design to local conditions allows the signal to better adapt to different environments and ensure road safety.
With the continuous progress of technology, the technology of traffic signals is also continuously updated. New detection technologies and intelligent control systems, such as SCOOT (Split Cycle Offset Optimization Technique), enable signals to better adapt to traffic changes and improve management efficiency. However, the application of these new technologies often requires high cost investment, including the costs of equipment procurement, installation and post maintenance. Therefore, when selecting signalization technologies and design solutions, a balance between performance enhancement and cost control needs to be found.
Traffic signal lights
The design of signal lights should not only be practical, but also consider the integration with the urban environment. In older cities with a long history, signal light designs may incorporate local cultural elements and architectural styles to harmonize with the cityscape, while in newer cities or modernized areas, clean, contemporary design styles are preferred. These different design choices reflect the personality of the city and influence the perception of traffic signals.
Cultural variations in different countries and regions can also be reflected in the design of traffic signals. Although the basic meanings of the colors red, yellow and green are more or less the same worldwide, there are still differences in some details. For example, in the United States and Canada, yellow signals indicate warnings; in Brazil, yellow lights convey a similar meaning. These differences ensure that traffic signals are better adapted to local cultures and usage to ensure road safety.
Traffic signals play a crucial role in modern transportation systems, and their role is mainly reflected in the following aspects.
Ensure traffic safety: through clear and uniform signal instructions, traffic signals reduce conflicts between vehicles and pedestrians at intersections, effectively prevent traffic accidents, and provide safety for road users.
Optimize traffic flow: Scientific and reasonable signal timing and coordination can minimize the waiting time of vehicles and pedestrians, reduce traffic congestion, and make traffic flow smoother and more efficient.
Distribute right of way: Using different signal phases, traffic signals distribute the right of way in each direction in an orderly manner, ensuring fairness and order in traffic operation.
Enhance traffic efficiency: Modern inductive signals and intelligent control systems are able to dynamically adjust the light hours according to real-time traffic data, making full use of road resources and improving overall traffic operation efficiency.
From the color meaning of the signal to the working mechanism, from the detection technology to the different types of functions, to the reasons for the differences in design and the important role, every aspect of the traffic signal contains science and wisdom. With the continuous progress of technology, future traffic signals will be more intelligent and efficient, using more advanced sensor technology, artificial intelligence algorithms and big data analysis to achieve accurate management of traffic and provide safer and more convenient protection for people’s travel. We also look forward to the continuous development of traffic signals, for the orderly operation of urban transportation continues to escort.
