Introduction

Traffic signals play a vital role in the busy modern urban traffic network. Traffic lights are power-driven traffic control devices that display lights that instruct traffic to take specific actions. They can guide vehicles, pedestrians and other traffic participants to pass in an orderly manner, effectively reducing traffic conflicts and congestion. Ultimately, it improves the safety of vehicle users and pedestrians and makes the most efficient use of available road space. We will list the classification and functions of traffic signals one by one, as well as the composition and working principles of traffic lights at typical intersections. In addition, the concept of “phase” of traffic lights is the core of understanding their working principles and traffic flow organization, which determines the order and duration of different traffic flows. This article aims to provide readers with a comprehensive and in-depth knowledge system of traffic signals, so as to better understand this seemingly simple but crucial traffic facility.

The role of traffic signals

The function of traffic signals is to control the movement of traffic, bicycles and pedestrians, especially at intersections, and to alert road users to special safety issues (for example, at level crossings or in front of schools). Traffic signals should achieve some or all of the following purposes:

• Provide safe and orderly movement: Traffic lights ensure that road users (including vehicles, pedestrians and cyclists) can pass through intersections safely and in an orderly manner through clear instructions.
• Improve traffic efficiency: Properly set traffic signals can control traffic flow in different directions and ensure that vehicles and pedestrians can pass in an orderly manner, which helps to reduce traffic congestion and waiting time.
• Reduce the frequency of accidents: Orderly passage can reduce traffic conflict points, thereby reducing the frequency of traffic accidents.
• Reduce overall delays: By optimizing the timing of traffic signals, optimizing the time ratio of driving on main roads and secondary roads, reducing the waiting time of vehicles at intersections, and reducing overall traffic delays.

Different traffic signals

Traffic signals are an important tool for directing road traffic. They can be divided into many types according to their functions and locations. Common types of traffic lights include:

Item	Motor vehicle traffic signals	Pedestrian traffic signals	Arrow traffic signals	Countdown timer
Photos

Motor vehicle traffic signals

The motor vehicle traffic signal consists of three circular(full ball) units of red, yellow and green patterns. It has three complete (circular) faces and indicates that vehicles can pass the relevant stop line under the instruction of the relevant green face lighting, but it does not impose any restrictions on direction, etc. Its main function is to guide the passage of motor vehicles, that is, the red light indicates prohibition of passage, the green light indicates permission to pass, and the yellow light indicates slow travel or warning.

Non-motor vehicle traffic signals(Pedestrian traffic signals)

Pedestrian signals are traffic signals designed specifically for controlling pedestrian traffic. Pedestrian facilities should be provided to improve the safety of pedestrians crossing the road. They are usually installed at intersections controlled by traffic signals. It provides pedestrians with a phase at which signals can be issued to take care of the needs of pedestrians. Pedestrian traffic signals can be activated by a relay pedestrian button or automatically (for example, to prevent the phase from being inconsistent with adjacent signals on the connected signal system). It also consists of red, yellow (if available), and green circular units with bicycle/pedestrian patterns inside. It is generally set at both ends of the crosswalk. When the red light is on, pedestrians and non-motor vehicles are not allowed to enter the crosswalk/intersection; when the green light is on, pedestrians and non-motor vehicles can pass.

Arrow traffic signals

When it is necessary to control vehicles for a specific movement (usually a left turn), a second traffic signal head may be set up next to the signal head that controls the movement of adjacent traffic. The second head should display red, amber and green arrows instead of full aspects. This arrangement avoids the more obvious full red aspect, which only stops the turn when other traffic has a green aspect. The arrow can point left or right, or upward to indicate straight-line movement. It uses arrow traffic signals to indicate different directions of vehicle or pedestrian flow to more accurately control traffic flow and direction.

Countdown traffic signals(Countdown timer)

In places where there are a large number of motor vehicles or long waiting times, in addition to red, amber and green digital signals, countdown timers can also be installed on each side of the intersection. Using the remaining time displayed by the traffic light countdown timer, drivers can turn off their engines while waiting for the red light, which helps reduce fuel consumption. When the red light is about to end, drivers can use the remaining time displayed by the traffic light countdown timer to start the vehicle in advance, thereby shortening the start time and improving the traffic capacity of the intersection. It can also be set up next to non-motorized vehicles and pedestrian signals. This type of timer system provides drivers and pedestrians with an accurate countdown, increasing road flow, reducing congestion at intersections and ultimately improving traffic conditions.

What’s phasing and different signal phase operation?

Next, we discuss traffic signal phase-related concepts, standard phase schemes, and discuss their impact on traffic efficiency and safety. A “signal phase” is the complete sequence of green, yellow, and all red indications that give an action (including going straight, turning left, or turning right to the east, west, north, or south). Each of the green, yellow, and all red cycles that make up a phase is called a “phase interval.” The series of signal phases that serve all possible movements at an intersection is a “cycle.” A cycle can consist of as few as two phases or as many as eight (or more) phases. The phase state list details the color state of the signal light (such as red, green, yellow) and its duration in that phase. The number of phases at an intersection depends on the specific conditions of the intersection, including factors such as the shape of the intersection, the number of lanes, and the traffic volume. Common phases include standard two phase operation, standard four phase operation, and standard eight phase operation.

Standard two phase operation

The simplest type of signal phase is the standard two-phase operation. Here, the main street entrances to the intersection are served by phase one and the secondary street entrances are served by phase two. The two-phase configuration is very efficient and works well in low-volume conditions, but does not allow for a separate turn phase, so two-phase systems are less commonly used at intersections with a high volume of turning (left-turning) traffic. Two-phase signals are often found in urban and rural areas where left-turn volume is low to moderate.

Standard four phase operation

In order to provide an independent left turn phase when there are a lot of left turn movement, a four-phase signal controller is designed. In a four-phase signal, all phases are continuous, which means that no two phases can be activated at the same time. It usually does not allow the movement within a phase to be timed separately, or in other words, the signal cannot enter the next phase until all movements within the current phase have timed out or interrupted. Its overall structure is called a “loop” because after completing a cycle, it returns to phase 1 and starts again. A typical four-phase plan is shown in the figure below.

Standard eight phase operation

Four-phase operation allows left turns to be handled individually, but does not allow for individual timing of each (different) action within a phase. This is important in situations where the relative volumes of a phase are unbalanced, where four-phase operation will maintain a phase even if one of the actions no longer has any demand. Eight-phase operation allows for individual timing of each action, for more efficient operation.

An eight-phase controller is like two four-phase controllers working together. As with a four-phase controller, phases 1-4 form one ring. Phases 5-8 form a second ring, so eight-phase controllers are often called “dual-ring” controllers. Each ring operates in sequence, meaning that at any time only one phase in a ring can be active and timed separately from the phases in the other ring. Phases can be skipped if there is no demand. All phases in a given ring should be collided. Each ring operates independently, with the only restriction that both rings must cross the barrier together. That is, any phase (1 and 2) in ring 1 on the left side of the barrier can be matched with any phase (5 and 6) in ring 2 on the left side of the barrier. However, any phase (1 and 2) in ring 1 on the left side of the barrier cannot be run together with any phase (5 and 6) in ring 2 on the right side of the barrier.

Traffic signals at typical intersection and how do they work？

Traffic signals at typical intersection

The signal configuration of an intersection needs to consider many factors, such as traffic volume, intersection size, number of lanes in different directions, and functional requirements. Among them, the motor vehicle traffic signals (fall ball red, yellow, and green) need to be set up with a set of three-color signal lights in each direction. If there are multiple lanes, the number can be increased appropriately to ensure that drivers in all lanes can clearly see the signal. For example, a four-way intersection with one or more lanes in each direction requires at least 4 sets of traffic signals. If the intersection allows left or right turns and has a dedicated turning lane, arrow traffic signal lights should be set up and each direction usually requires at least one left turn arrow traffic signals(right turn arrow traffic signals – if requires). That is, a four-way intersection requires up to 8 arrow signal lights (two in each direction, one left turn and one right turn). Countdown devices are usually installed next to motor vehicle traffic signals or pedestrian traffic signals to help drivers and pedestrians understand the remaining waiting or passing time. Generally speaking, a four-way intersection requires at least 4 countdown devices. If the intersection design includes non-motorized vehicle lanes or dedicated bicycle lanes, each direction requires a non-motorized vehicle traffic signals and two pedestrian signals. Below is the signal light configuration at a typical intersection.

Items	Model	Photo	Product	LED Qty (PCS)	Light Intensity (MCD)	Wavelength (NM)	Power (W)	Input Voltage (DC/VAC)	Quantity
No.1	JD300-3-ZGSM-3-RYG		Full Ball Traffic  Signals	R: 168 Y: 168 G: 168	R: 5000~7000 Y: 5000~7000 G: 8000~13000	R: 625±5 Y: 590±5 G: 500±5	≤8 ≤8 ≤10	100-240V AC (±10%), 50/60Hz 12/ 24V DC	4
No.2	FX300-3-ZGSM-3-RYG		Arrow Traffic  Signals	R: 96 Y: 96 G: 96	R: 5000~7000 Y: 5000~7000 G: 8000~13000	R: 625±5 Y: 590±5 G: 500±5	≤5 ≤5 ≤7	100-240V AC (±10%), 50/60Hz 12/ 24V DC	4
No.3	DJS300-3-ZGSM-1-88RG		Countdown Traffic  Signals	R: 84 G: 84	R: 5000~7000 G: 8000~13000	R: 590±5 G: 500±5	≤2 ≤2	100-240V AC (±10%), 50/60Hz 12/ 24V DC	4
No.4	RX300-3-ZGSM-2-RG		Pedestrian traffic signals	R: 80 G: 82	R: 5000~7000 G: 8000~13000	R: 590±5 G: 500±5	≤8	100-240V AC (±10%), 50/60Hz 12/ 24V DC	8

How do they work?

At each entrance to an intersection, vehicles have three directions they can go which is called moves: right, through, or left. Right and through are usually grouped together as a single move, so a typical four-way intersection has eight vehicle and four pedestrian moves. These moves can be grouped into phases of a traffic signal. For example, left turns in opposite directions can be grouped into a single phase because they can be done at the same time without conflict. Traffic engineers use circle and barrier diagrams to outline how the signals operate in different phases. Here is a ring and barrier diagram for our example intersection. Phase 1 is for left turns in the north-south direction, and phase 2 is for straight travel in the north-south direction. Note that the timing of the opposite direction moves in phases 1 and 2 can be inconsistent, i.e., a south-to-north left turn can end early and be replaced by a north-to-south straight move. But there is a barrier between phases 2 and 3, so they must end at the same time. Phase 3’s east-west left turns and phase 4’s east-west straight moves also operate in the same way, so we won’t go into detail here. The following diagram will give you a better understanding of the different moves in the four/eight phases.

Summary

This article mainly introduces the main functions of traffic signals, the classification of different traffic signals, and the composition and distribution of typical crossroad lights. We also introduce the theory of traffic signal phases and understand their actual application and application characteristics in intersections. At the same time, we also apply these theories to typical intersections to help us understand the working principles of traffic lights, etc. I hope that everyone can deepen their understanding of traffic lights through this article, suppliers can better serve customers, and customers can better and more accurately choose signals to arrange their own projects. Contact us for more information.

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