1. How Traffic Control Centers Watch Traffic and Road Conditions
Traffic control centers measure the amount of traffic and the state of the roads. According to the Ehime Prefectural Police, they use vehicle detectors placed on major roads and at intersections to count cars [1]. At key intersections, television cameras watch the condition of the road. The center also collects information from police officers and patrol cars [1]. This gathered information is processed by large computers. It is used to control traffic signals and to provide information on electronic signs and radio broadcasts [1]. In short, the center connects four tasks in one room: collecting data, thinking about it, moving the signals, and sharing news. But how do these numbers actually change the signals?
2. How Green Light Length and Signal Timing Change With Traffic
The length of the green light and the timing with the next signal change based on traffic conditions. The Kanagawa Prefectural Police explains that the time allocated to green lights for each direction, and the timing for when adjacent signals turn green, are adjusted in real time as traffic changes [2]. The Police White Paper states that data on traffic volume and driving speed, collected by vehicle detectors, is analyzed. The results are then used to control signals and provide traffic information [3]. Detailed explanations of "system control" (linking signals together) and "offsets" (the difference in the start time of green lights) are covered in other notes. The National Police Agency’s materials also mention a method called "profile signal control." This method predicts the traffic volume arriving at a downstream intersection based on the volume measured at an upstream intersection, then sets the green time accordingly [8].
3. How Linking Traffic Signals Reduces CO2, Congestion and Accidents
Linking signals helps reduce congestion, prevent accidents like rear-end collisions, and lower carbon dioxide (CO2) emissions and noise. The Ehime Prefectural Police lists these benefits, noting that fewer stops mean less CO2 and noise [1]. According to the National Police Agency, the cumulative reduction in CO2 from centralizing signal control (connecting them to a center) was 7.04 million tons for the fiscal years 2015 to 2019 [8]. This is the total for five years, not the amount for one year. Moving a single signal does not produce a visible change on its own. However, when signals across a whole city are linked, the reduction amounts accumulate over time.
4. The First Traffic Signal Control Experiment in Ginza in 1965
In 1961, a traffic information center using the police telephone network started. It covered about 20 major routes, with the 1964 Tokyo Olympics as one of its goals [4]. This was a facility for gathering and sharing information, which is different from a traffic control center that moves signals. Then, in 1965, the first attempt to control a street network as an "area" began. A wide-area traffic signal control system started in the Ginza district, covering about 1 square kilometer (about 0.4 square miles) [4]. This was an attempt to control signals across a wide range of the street network. It was the first time a counting-type electronic computer was used for traffic control [4]. The phrase "about 1 square kilometer" refers to area. It means the same size as a square with 1-kilometer sides, but the actual shape was not necessarily a square.
5. How the Ginza System Spread to Control Centers Across Japan
According to the paper by Yoshishiro Sawa, a system improved on the Ginza model was completed in 1968 for central Tokyo. This was integrated with the traffic information center’s system to become a "traffic control system." It is explained that this became the system for traffic control centers, which began to be installed in various places starting in 1971 [4]. By the fiscal year 1984, centers were newly established in Nagaoka City and Sasebo City. Centers were set up in 72 major cities, including prefectural capital cities [5]. At the end of that fiscal year, out of 116,616 traffic signals nationwide, 31,162 signals (26.7%) were controlled by center computers [5]. If you divide 31,162 by 116,616, the result is about 0.267. This means roughly 1 out of every 4 signals was computer-controlled. However, this is a figure from the end of fiscal year 1984, not the current percentage.
6. How the FAST System Creates Green Lights for Emergency Vehicles
FAST (Field Access Support System) is a signal control system that prioritizes emergency vehicles like ambulances. Its aims are to shorten the time it takes to arrive at the scene and to prevent accidents during emergency driving [6]. According to the Police White Paper (2010 edition), 13 prefectures had installed this system by the end of fiscal year 2009 [6]. This is a figure from that time. The current number is not known from the materials used here. Besides FAST, the UTMS (Urban Traffic Management System) includes systems to inform drivers about congestion and to prioritize buses [7].
7. How to Observe Linked Traffic Signals Yourself
You can try this on your way home or while shopping. From the sidewalk, look for places where the signals in the direction you are traveling turn green one after another. Do not go out onto the road. By comparing places where lights turn green in sequence with places where they do not, you can observe the differences in signal timing. You can also visit a center. The Metropolitan Police Department’s traffic control center allows group visits (up to 36 people) with a prior phone reservation. It is open Monday to Friday (excluding holidays and year-end/New Year), with 4 sessions per day, each lasting about 50 minutes [9]. Conditions may change, so please check the official page for the latest information.