What is an Actuated Traffic Signal?
When driving, there are cases where a traffic light changes as soon as your car approaches an intersection at night or on roads with little traffic.
Many of these traffic lights are actuated traffic signals. By adjusting the signal changes according to traffic conditions, they play a role in smoothing traffic flow and reducing congestion and unnecessary waiting time.
This article explains the mechanism and how to identify actuated traffic signals.
What is an actuated traffic signal?
An actuated traffic signal is a traffic signal that detects vehicles or pedestrians using sensors or buttons and automatically adjusts the signal display time based on that information.
Standard traffic lights switch between green, yellow, and red at fixed intervals. However, with actuated traffic signals, the signal timing changes according to traffic volume.
For example,
maintaining a red light for roads where no cars are present
switching to a green light when a car is detected
extending the green light for directions with higher traffic volume
are types of control performed.
Therefore, efficient signal operation is possible even at intersections with low traffic volume.
Actuated traffic signals are classified into the following two types.
Fully actuated traffic signals: Vehicle detectors are installed on both the main road and the side road, and the green time is varied according to traffic volume.
Semi-actuated traffic signals: Vehicle detectors are installed only on the side road, and green time is set for the side road only when a vehicle is present there. Pedestrian push buttons are often installed as well.
Some actuated signals change even if there are no vehicles or pedestrians after a certain amount of time has passed, or only operate during specific times such as at night.
Mechanism of vehicle-actuated traffic signals
Vehicle-actuated traffic signals use sensors installed on or beside the road.
Typical detection methods include the following.
1. Ultrasonic method
Ultrasonic sensors installed on the road detect vehicles. Because there is no need to dig up the road, it is characterized by being relatively easy to install and update. To identify vehicle-actuated traffic signals in Japan, one can check if there is an ultrasonic sensor before the vehicle stop position on the minor road.
2. Loop Coil Type
Electric wires (loop coils) are embedded in the road pavement, and they detect when a vehicle passes over or stops on them. This is not very common in Japan. It is the most common method in overseas countries such as the United States.
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Since motorcycles may be missed by standard vehicle sensors, push buttons for motorcycles are often provided alongside them.
Mechanism of Pedestrian-Actuated Traffic Signals
These are classified as a type of barrier-free traffic signal. It is a mechanism that automatically or via a button extends the green light when people who walk slowly, such as the elderly, are crossing the crosswalk.
High-precision pedestrian sensors (image detectors such as cameras or millimeter-wave radar) detect the movement of pedestrians on the crosswalk.
Types include pedestrian-actuated traffic signals (pedestrian sensors) and traffic signals for the elderly, etc. (push-button signals for green light extension, with white box buttons). They are sometimes called "pedestrian support signals."
Incidentally, standard push-button signals (yellow box buttons) that simply change the pedestrian signal to green when a pedestrian presses the button are not included as pedestrian-actuated traffic signals.
For more details, please refer to the following article.
Signage
To clearly indicate that it is an actuated traffic signal, signs stating "Actuated" or similar may be displayed on signs installed under the traffic signal body or on the arm. This is not mandatory.
The method of display varies by prefecture; some, like Tokyo, do not display it at all, while others may display "Detecting" via LEDs on the sign when the sensor reacts to alleviate the anxiety of drivers waiting for the signal.
Although many local governments describe even semi-actuated signals as "actuated," Gunma Prefecture has locations where it is meticulously labeled.
When the sensor detects a vehicle, "Detecting" is displayed on the LED below.
Although there is no 'Actuated' display, when the sensor detects a vehicle, it displays 'Detecting'
History of Actuated Traffic Signals
In Japan, the first actuated traffic signals were installed successively at intersections in Tokyo and Yokohama in March 1963 (Showa 38).
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