JAPAN TRAFFIC MANAGEMENT TECHNOLOGY ASSOCIATION

Contents
Introduction‥ ‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 1Part I
1. Roles of traffic signals‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 2
2. Numerical analysis of traffic flow‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 3
3. Basics of traffic contro‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 6(1) Importance of traffic control‥ ‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 6(2) Signal phase ‥ ‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 7(3) Three cornerstones of traffic control‥ ‥‥‥‥‥‥‥‥‥‥‥‥ 8(4) Clearance intervals ‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥10(5) Pedestrian crossing time‥ ‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥ 11
4. Point, line, and area traffic control‥ ‥‥‥‥‥‥‥‥‥‥‥‥‥13
5. Traffic control centers‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥16
6. History of traffic signals‥ ‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥19
7. Q&A‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥25
8. Relationship between the number of traffic signals and the number oftraffic accident deaths‥ ‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥29
9. New traffic control system‥ ‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥31
Part II (an in-depth study of traffic signals)
1. Signal phase‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥33
2. Types of signal control systems‥ ‥‥‥‥‥‥‥‥‥‥‥‥‥‥37(1) Traffic-actuated control system‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥37(2) Coordinated signal control system‥‥‥‥‥‥‥‥‥‥‥‥‥‥43(3) Area traffic control system‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥46
3. Structure of traffic signals‥ ‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥51(1) Signal controllers‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥51(2) Signal lights‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥52(3) Push-button boxes‥ ‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥52(4) Vehicle detectors‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥‥53
4. Comprehensive checklist for traffic signals‥ ‥‥‥‥‥‥‥‥‥‥56

Introduction
At intersections, traffic flows merge, diverge, andintersect. Such traffic phenomena are further
complicated by the presence of pedestrians. Imagine
what roads would be like if we had no traffic signals.
Not only would the roads be overflowing with vehicles
traveling in different directions, but pedestrians would
be forced to weave their way through this traffic,
making traffic accidents and congestion a regularoccurrence. Traffic signals play a variety of essential
roles in preventing traffic accidents and ensuringsmooth driving.
Providing an easy-to-understand summary of key
information, this pamphlet is intended to raise readers'interest in traffic signals as well as to help them acquirea basic understanding of traffic signals.
An overview of traffic signals is provided in Part I, whilemore detailed explanations of how they operate can befound in Part II.

1

Part I

1. Roles of traffic signals
⿓Preventing traffic accidents

Traffic signals ensure a temporal separation of traffic
flows moving in different directions. They control traffic
flows to prevent vehicles from colliding with or
obstructing other vehicles and pedestrians, thereby
protecting them from traffic accidents.

⿓Ensuring smooth traffic flow

Traffic signals are operated at an optimal timing basedon the traffic volume to ensure a smooth flow of traffic.

⿓Improving the traffic environment

Smooth traffic reduces the number of vehicle stops andensures a stable traffic flow, thereby reducing trafficrelated problems, such as exhaust emissions andnoise. It also contributes to a reduction in carbon
emissions.

Buoooooo!

22. Numerical analysis of traffic flow
The analysis of traffic movement is necessary for thecontrol of traffic signals. To optimize the control of
traffic signals, we need to determine not only how
many vehicles are traveling in a particular direction andhow they are traveling, but also where traffic is being
impeded as a result of congestion. To provide
information to the signal devices, it is also necessary to
numerically analyze the traffic flow. Since it is
impossible to collect the necessary information
manually in every urban area, we need to develop
systems that can collect such information automatically.
In this section, we provide a brief explanation of how
traffic flow can be numerically analyzed.

⿓Quantifying traffic flow

Expressions such as "light traffic" and "heavy traffic"
are too ambiguous for a rigorous assessment of traffic.
To ensure the optimal management of traffic signals,
we need to conduct a numerical analysis of the traffic
flow. Generally speaking, the following three methods
can be used to measure traffic.
The first method measures traffic volume by counting
the number of vehicles that pass a specific point withina predetermined amount of time. The traffic volume
grows as the number of vehicles increases. However,a traffic volume that exceeds the road capacity resultsin traffic congestion, thereby reducing the traffic
volume.

3

Traffic volume

2. Numerical analysis of traffic flow

The second method measures traffic speed byaveraging the speeds of vehicles that pass a specificpoint within a predetermined amount of time. The traffic
speed is low if vehicles move slowly due to traffic
congestion, with a speed of zero indicating that thevehicles have stopped moving altogether.

Traffic speed

The third method measures traffic density by
calculating the number of vehicles traveling within a
specific road section. Traffic density increases oncongested roads, and it reaches a maximum if vehicles
stop moving due to traffic congestion.

Traffic volume, traffic speed, and traffic density are
the three measures used to quantify traffic flow.

Traffic density42. Numerical analysis of traffic flow

⿓Measuring traffic flow with vehicle
detectors

Devices called "vehicle detectors" are used toautomatically measure traffic flow without carrying out
any manual operations. Vehicle detectors generally
emit ultrasonic sound waves from above to detectvehicles passing underneath by using the difference
between the time required for sound waves to reflect
back from the bodies of the vehicles above the roadsurface and the time for waves to reflect back from theroad surface. In addition, detectors can also assess
traffic conditions by converting the vehicle detection
data into electric signals (pulses) and measuring them.

(c) Traffic density
Traffic density is measured by calculating thepercentage of the measurement section that is
occupied by vehicles. Since traffic density cannot bemeasured using a single ultrasonic vehicle detector, it
is estimated from the pulse lengths measured bymultiple detectors and the traffic speed calculated fromthe traffic data.
Generally speaking, traffic is considered to becongested in sections with high traffic density.

(a) Traffic volume
Vehicle detectors can measure traffic volume byconverting the sound waves reflected back fromvehicles passing underneath into electric signals(pulses) and then counting the number of pulses
generated within a predetermined amount of time.
(b) Traffic speed
Ultrasonic vehicle detectors calculate the traffic speed
based on the pulses that they measure. Under normal
traffic conditions, vehicles pass under a detector in ashort period of time, resulting in short pulses being
repeatedly generated. During traffic congestion,
vehicles pass under the detector more slowly, resulting
in the pulses being longer and less frequent.

Ultrasonicwave

Electric signals (pulses)
Normal traffic
conditions
Time
Traffic congestion

Feeling irritated!

Traﬃc moving
slowlyFeeling irritated!

Traﬃc moving
slowlyTime
During traffic congestion, the electric pulses become longer as the number of vehicles
passing within the predetermined amount of time decreases.
5

3. Basics of traffic control(1) Importance of traffic control
The illustration on the right shows how traffic moves at
an intersection without traffic signals.

The vehicles moving straight ahead need tosimultaneously pay attention to vehicles coming fromtheir left, their right and in front of them to determine
when they can move forward.
The length of time that they have to wait to find theright timing may be short if the traffic volume is small.
However, heavy traffic increases the wait time. During
heavy traffic, some vehicles may try to force their way
into the intersection, raising the risk of traffic accidents.
Also, vehicles moving in different directions may end
up obstructing each other in the intersection, thereby
blocking traffic.
Installing traffic control signals prevents vehicles
moving in different directions from obstructing eachother. Also, when the signal turns green, vehicles
moving straight ahead only need to pay attention to
oncoming vehicles. This improves traffic safety.
As this example demonstrates, traffic signals play a
key role in ensuring a safe and smooth flow of traffic atintersections by controlling the traffic to create a
temporal separation of traffic flows moving in different
directions and to prevent vehicles from colliding with or
obstructing each other.

63. Basics of traffic control(2) Signal phase
Let's consider how traffic flows moving in different
directions are controlled.
At an intersection, vehicles moving in different
directions are given right-of-way in turns according to
the traffic signals there. In other words, a green signal
light allows only vehicles and pedestrians moving in a
specific direction to cross the intersection. The periodof time during which traffic moving in a specificdirection is given right-of-way is called the signal
phase.

Phase AAt an ordinary intersection, the traffic signals operateaccording to phases A and B alternately. Known as a
two-phase control system, this is the system that ismostly commonly used in Japan.
At intersections where an especially large number ofvehicles tend to turn right, phase C for right-turning
vehicles may be inserted between phases A and B, as
shown in the figure on the right. This system, which
distinguishes traffic flows traveling in three different
directions, is called a three-phase control system.

Phase B

Phase C

Traffic flow with right-of-way
Stop

7

3. Basics of traffic control(3)Three cornerstones of traffic
control
The most crucial aspect of operating traffic signals iscoordinating the timing of their signals. The following
three parameters can be used to set this timing: cycle
length, split, and offset.

青黄

⿓Cycle length

The time it takes for a set of traffic lights to change
from green to yellow to red and back to green again iscalled the cycle length, which is expressed in seconds.
A short cycle length reduces the traffic volume, thereby
causing traffic congestion. In contrast, a long cycle
length wastes time. The optimal cycle length isdetermined based on the traffic volume, the size of theintersection, and the pedestrian crossing time.
Generally speaking, longer cycle lengths are set forintersections with heavy traffic.

⿓Split
The amount of time within a single cycle length that isallocated to each signal indication is called the split,
which is represented as a percentage of the cycle
length. Using the same split time for busy main roads
as that for quiet subsidiary roads would result in
wasted time. Given this, split times should be allocatedbased on the traffic volume. If, for example, the cycle
length is 100 seconds, 60% (60 seconds) of this time isallocated to the main road while 40% (40 seconds) is
allocated to the subsidiary road.

Cycle length

赤

40%

60%

8

3. Basics of traffic control

⿓OffsetTo enable vehicles traveling on a main road to passthrough intersections smoothly without having to stop at
signals, the traffic lights are designed to turn green atslightly different times at adjacent intersections. This
time difference is called the offset, which is represented
as a percentage of the cycle length or in seconds.
For example, if traffic signals A and B both have acycle length of 100 seconds and the time difference
between them turning green is 10 seconds, there is anoffset of 10%—or 10 seconds—between them.

B

A

As the cycle length, split, and offset are essential tocreating a smooth flow of traffic, they are referred to as
the three cornerstones of traffic control.

OffsetGreen

YellowRed

A
Cycle length
B

9

Red

Green

Yellow

Red

3. Basics of traffic control(4) Clearance intervals
In this section, we focus on how vehicles are prevented
from colliding with each other when the traffic signals
change.
When the traffic signals switch from phase A to phase B,
vehicles in phase A must either stop before the stop lineor cross the intersection before phase B begins in order
to avoid colliding with vehicles traveling in a different
direction. In light of this, a period of time is set aside
between phases A and B to ensure that the intersection
is clear of vehicles. The time required to allow vehicles
to leave the intersection is called the clearanceintervals, which is represented by the aggregate of theyellow light time and the all-red light time.
The length of an intersection's clearance intervals
varies depending on its shape and size.

Phase A

Passing throughStopping
Yellow signal

Stopping

⿓Yellow light time

When a traffic light changes from green to yellow,
some vehicles can stop safely in front of the stop line
while others cannot. The yellow light time is set toenable vehicles that are unable to stop in front of thestop line to pass through the intersection safely within
the specified amount of time.

⿓All-red light time

Stopping
All-red signals

Stopping

The all-red light time is set to allow vehicles still inside
the intersection, including those waiting to turn right, toleave before the next signal phase begins.
If the yellow and all-red light times are too long,vehicles waiting at the intersection are likely to startmoving before the signal turns green and somevehicles may not stop at the yellow light. In contrast, if
the times are too short, some vehicles may still be
inside the intersection when the next signal phasebegins. Given this, the yellow and all-red light times
need to be set appropriately.

Phase B

10

3. Basics of traffic control(5) Pedestrian crossing time
The pedestrian green light time and the flashing green
light time constitute the time required for pedestrians tocross the road safely.

⿓Pedestrian green light time

The amount of time that pedestrians require to crossan intersection varies depending on its length. The
amount of time required is generally calculated byassuming a walking speed of 1 m per second.

⿓Flashing green light time

The flashing green light time is the amount of time thatpedestrians in the middle of crossing a road during thepedestrian green light time will require to reach theother end of the intersection or return to the starting
point. The amount of flashing green light time varies
depending on the length of the intersection. A green
light generally flashes for a period of 4 to 10 seconds.
If the pedestrian green light time for an intersection is
too short, pedestrians are unable to cross it. If it is too
long, right- and left-turning vehicles are unable tomove, thereby causing traffic congestion. Since this inturn results in a long cycle length, irritated drivers andpedestrians waiting at a red light may cause accidents.
Therefore, the pedestrian green light time needs to be
set appropriately.

11

Note
Importance of seconds in traffic
control
A difference of just two seconds…

During rush hour, vehicles pass through an intersection
at a rate of about one vehicle every two seconds. Thismeans that reducing the green light time by two
seconds will prevent one vehicle per cycle fromcrossing the intersection. Repeated 30 times, this will
result in 30 vehicles being kept waiting at theintersection, generating a queue with a length of 150 to
200 m.

…It's safe to say that two seconds matter.

Seconds

12

4. Point, line, and area traffic control
When traffic signals were initially introduced in Japan,
traffic control was implemented independently at eachintersection (point traffic control).
As more traffic signals were installed, it became
necessary to coordinate the operations of adjacent
traffic signals (line traffic control).
As the number of traffic signals continued to grow,horizontal as well as vertical coordination between
signals were taken into consideration (area traffic
control).
These traffic control systems (point, line, and area
traffic control) serve as the basis of signal control.

⿓Point traffic control

In the early days of traffic control, green, yellow, andred lights were displayed according to a single, fixed
temporal pattern.
Subsequently, the green light time was set inaccordance with the daily traffic flow to ensure asmoother flow of traffic. Nowadays, for example, thegreen light time is sometimes set to follow threedifferent patterns based on the following three traffic
patterns: heavy traffic during the morning and evening
rush hours; normal traffic during the day; and low traffic
at night. This type of signal control system is called
multistage control.

13

4. Point, line, and area traffic control

At intersections where the traffic volume changes too
rapidly for traffic to be controlled with a multistage
control system, the green light time is set to follow as
many patterns as necessary in accordance withchanges in the traffic volume. This type of signal
control system is called traffic-actuated control.
Another type of signal control is called push-buttonactuated control, which was introduced to allow thetraffic signal to turn green only when a pedestrianpushes the button.

This type of control can be implemented only for traffic
signals that have the same cycle length. A computer
system is required for this to work for signals withdifferent cycle lengths. To this end, several patterns ofcycle lengths, splits, and offsets are created in advanceand stored in the computer system memory. Based on
the actual traffic conditions, the appropriate pattern canthen be chosen from among the stored patterns toprovide the traffic signals with the instructions required
to ensure an optimal green light time.

As this demonstrates, a series of traffic signals that arecontrolled in accordance with traffic volume orpedestrian needs have been developed in recent
years.

⿓Line traffic control

Systems for coordinated control, or line traffic control,
have been developed to change a series of adjacent
traffic signals to green in sequence so that vehicles
can pass through intersections without having to stop.
These systems are designed to coordinate theoperation of adjacent traffic signals so that a signal willturn green after a predetermined amount of time has
passed since the immediately preceding signal turned
green. This allows vehicles to travel more smoothly.

14

4. Point, line, and area traffic control

⿓Area traffic control

In urban areas that are covered with an extensive road
network, point and line traffic controls are not fully
effective.
Such areas require a traffic control system capable ofcovering areas that include both vertical and horizontal
roads. To meet this need, vehicle detectors that can
detect traffic flow have been installed at key points toprovide the computer system with data on theconstantly changing traffic conditions. Based on thisdata, the computer system performs calculations fortasks such as those listed below to provide the traffic
signals with the instructions required to ensure an
optimal green light time.
- Reducing the number of traffic stops- Reducing the wait time
- Reducing the queue length
As this demonstrates, traffic signal control has evolved
into more advanced systems. Today, point, line, andarea control systems are used in a variety of ways
based on the traffic conditions in different areas.

15

No matter how sophisticated and advanced
technologies may become, the key issues for traffic
signals are when they should turn green and how longthey should remain green. The answers to thesequestions are, and always will be, crucial in preventing
traffic accidents and reducing traffic congestion.

5. Traffic control centers
Traffic control centers have two major roles to play: theefficient management of traffic flows and the utilizationof traffic information. To fulfill these roles, these centersneed to collect large amounts of data. To this end, they
use resources such as vehicle detectors, CCTV
cameras, and police cars to collect the data required toensure traffic safety and efficiency and share traffic
information. With our society becoming ever more
dependent on cars, the roles played by traffic control
centers have become more important than ever.

Efficientmanagementof traffic flow

Create safe,
efficient
traffic flow

- Create safe, efficient vehicle flow
- Prevent traffic accidents and reduce pollution- Improve economic performance, including by
reducing gasoline consumption

Managetraffic in- Control traffic in the event of a disaster or otheremergencies such incidents

Roles of traffic
control centers

Utilization of
traffic
information

Providetraffic
information- Provide traffic status data and road information

Analyzetraffic
information- Conduct statistical analysis of traffic conditions16

5. Traffic control centers

Adjacent traffic control center
Exchanges information with other control centers.
Helicopter

CCTV camera
Installed at key intersections tomonitor traffic via TV monitors intraffic control centers.

Vehicle detector
Installed at key points to measuretraffic volume, speed, etc., and senddata to traffic control centers.

Traffic control center
Control room

Machinery room

Roadside radio transmitter
Transmits audio messages about
traffic conditions and regulations
to drivers in a specific area via carradios.

Radio broadcasting
Pr ov i d e s i nf o r m at i o n o n t r af f i c
conditions and regulations at specifictimes via general radio broadcasts.

17

Police car

Infrared beacon
Provides traffic congestion information andother traffic data to car navigation systems
compatible with the Vehicle Information
and Communication System (VICS) bymeans of messages and graphic images.
Traffic information sign
Provides dr iver s with traf f ic
infor mation, including travel
times.

Traffic signal
Automat ic ally c ont rols t he green,y e l l o w, a n d r e d s i g n a l t i m e s v i acomputers in the traffic control centers.

5. Traffic control centers

Providing traffic information
Traffic control centers collect traffic data, including thetraffic volume and speed, via vehicle detectors installedat key points along roads. They also collect data on
construction works, events, traffic accidents, and otherincidents from a variety of sources, such as the video
footage from CCTV cameras installed at key points,
wireless communications from police cars, andinformation from various related organizations.
This data is analyzed by computers so that the traffic
congestion status can be displayed on map displays inthe traffic control centers. This data is also provided todrivers and other people in an easy-to-understandformat by methods such as the following.
- Provision of announcements for large-scale areas via
general radio broadcasts- Provision of information within a specific area via carradios (using Roadside radio transmitters, which
provide traffic information at 1,620 kHz).
- Provision of information via traffic information signs
installed at key points using messages and graphic
images.
- Provision of information via infrared beacons andother devices to VICS-compatible car navigation
systems by means of messages and graphic images.

Roadside vehicle detectors
Collect information

Traffic control centers

Roadside traffic information
supply devices
Share information

Drivers

Operations to provide information via Roadside radiotransmitters, traffic information signs, and VICScompatible car navigation systems are performed
automatically by computers in the traffic control centers
based on the analysis results.

18

6. History of traffic signals
1868

⿓World's first traffic signal installed

The world's first gas-lit traffic signal for controlling
traffic was installed in London, England.
Equipped with two colored lights (green and red), thissignal used gas as its light source.
1930

⿓Japan's first traffic signal installed

Japan's first electric traffic signal was installed at the
Hibiya intersection in Tokyo. Imported from the UnitedStates, this device was equipped with three colored
lights (green, yellow, and red). Unlike today's signals,
however, the yellow light came on after both the green
and red lights.
In December of the same year, the first Japanesemade automatic traffic signals were installed at theintersection in front of Kyoto Station and two otherintersections. These were Japan's first traffic signals to
be installed on the four intersection corners opposite
the direction of traffic.

Japan's first traffic signal

19

6. History of traffic signals

1934

⿓Push-button traffic signals installed

The first Japanese traffic signals to be designed toallow school children to change the lights by pushing abutton so that they could cross the road were installedat two intersections (Umeyashiki and Rokugocho) on
the Tokyo First Keihin Highway.
1955

⿓Traffic signal for the visually impaired
installed

A traffic signal that used a bell sound to inform thevisually impaired that they could cross the road was
installed for the first time in Japan in Higashidacho,
Suginami-ku in Tokyo. Various other types of signals
were subsequently developed, but they were finallyconsolidated into two types in 1975: signals that use
melodies and signals that use artificial sounds (e.g.,bird songs). Since 2003, efforts have been made tounify these signals and use signals that exchange theartificial songs of different birds.** A pair of traffic signals with speakers installed
opposite each other on either side of a pedestriancrossing to alternately emit different sounds ("cheepcheep" and "coo-coo").

Bird'ssong

1961

⿓Metropolitan Police Department's Traffic
Information Center established

In 1961, the Metropolitan Police Department
established a Traffic Information Center to display
traffic congestion data collected from police officers bytelephone on a large map and to provide drivers withcongestion information mainly via radio broadcasts.
1963

1963

The Metropolitan Police Department introduced the SemiAutomatic Traffic Information and Control (SATIC) systemdesigned to provide data on traffic congestion levels rated
on a five-point scale. This data was sent manually fromtraffic congestion alarms to the Traffic Information Centerand then automatically displayed on a map.

Japan's first fully actuated traffic signal, which changes
the signal display time in accordance with the traffic
volume, was installed at the Atago 2-chomeintersection in Tokyo.

⿓SATIC system introduced

⿓Fully actuated traffic signal installed

20

6. History of traffic signals

1963

⿓Line-coordinated automatic traffic
signals installed

Japan's first line-coordinated automatic traffic signal
system was installed in Tokyo to control multiple traffic
signals along a traffic lane in accordance with traffic
volume.
1965

⿓Ultrasonic vehicle detector installed

Ultrasonic vehicle detector

Japan's first vehicle detector to use ultrasonic waves todetect vehicles was installed in Tokyo.
1965

⿓Pedestrian traffic signal featuringpedestrian symbols installed

A pedestrian traffic signal featuring pedestrian symbols
was installed at the intersection in front of the Shinjuku
Isetan Department Store in Tokyo to control pedestrian
traffic separately from vehicles and to conduct a teston having the green light flash at the end of the signal.
1966

⿓Area traffic control system implemented

Japan's first computer-based area traffic control system
was implemented at 36 intersections in Ginza, Tokyo.
In the same year, the National Police Agency drafted
its standard specifications for traffic signals.

Traffic signal with pedestrian symbols

1969

⿓Scramble intersection implemented

Japan's first scramble intersection, which allows
pedestrians to cross an intersection diagonally inaccordance with the pedestrian signals, wasimplemented at the Kokai intersection in Kumamoto
City.

Scramble intersection21

6. History of traffic signals

1970

⿓All-red traffic signal system introduced

The meaning of the yellow signal was revised, with allred signals being displayed after the yellow signal sothat vehicles approaching the stop lines at anintersection can pass through the intersection.
1971

⿓Traffic control center establishedJapan's first traffic control center was established in
Fukuoka City.

Control room

1971

⿓Center line shift system introduced

A center line shift system was introduced in Gifu
Prefecture to shift the center lines on highways thathave a notable difference in traffic volume on their
upstream and downstream lanes, thereby reducing
uneven traffic congestion in one direction.

Machinery room

Traffic control center

1973

⿓Bus priority traffic control system
implemented

A bus detector was installed at the Kami-Iida Shako
Minami intersection in Nagoya City to introduce
Japan's first traffic signal control system to prioritize
buses.
1975

⿓Parking guidance system introduced

Vehicle detectors were installed at the entrance andexit of every parking area in Naruto City, Tokushima
Prefecture, to automatically collect data on how full the
parking areas are and to display this data on roadsidevariable message display boards.

22

6. History of traffic signals

1981

⿓Variable message signs introduced

The Metropolitan Police Department introduced
variable message signs that provide traffic information
to drivers by displaying messages and graphic images
that are centrally controlled by traffic control centers.
1983

⿓Roadside radio transmitters introduced

The Metropolitan Police Department began providing
drivers with detailed audio traffic information via carradio broadcasts (1,620 kHz) from antennas installed
along the roadsides.
1987

Variable message sign

⿓Travel-time measurement system
introduced

Osaka Prefecture introduced a travel-timemeasurement system that provides drivers with traveltime information via information boards installed along
the highways.

Roadside radio transmitters23

6. History of traffic signals

1990

⿓Elderly-actuated push-button traffic
signals introduced

Kyoto Prefecture introduced elderly-actuated pushbutton traffic signals that are designed to extend thepedestrian green light time when the radio waves
emitted from the pendants worn by senior citizens andphysically disabled people are detected so as to ensure
their safety.
1992

⿓Infrared beacons introduced

Kanagawa Prefecture introduced vehicle detectors
that, in addition to being able to perform standard
vehicle detector functions, are also equipped with afunction for establishing two-way communication with
in-vehicle units.

Elderly-actuated push-button box

1994

⿓LED signal lights introduced

Aichi and Tokushima Prefectures introduced Japan's
first traffic signal lights to use light-emitting diode (LED)elements.
2001

⿓Fast emergency vehicle preemption
systems introduced

The Metropolitan Police Department introduced fast
emergency vehicle preemption systems (FAST) to
provide priority right-of-way to emergency vehicles.
Initially, only police vehicles had this priority right-of-way.
Subsequently, the Okayama City Fire Department's
ambulances were given priority right-of-way in 2003 in
Okayama Prefecture.
2013

⿓High-performance infrared beacons
introduced

With a view to further developing signal control and traffic
information technologies, high-performance infraredbeacons were introduced to not only provide traffic signal
information, but also collect probe data by increasing thecapacity to communicate with in-vehicle units.

Infrared beacons2017

⿓New cost-efficient traffic signals
introduced

Equipped with smaller lights capable of delivering thesame luminosity, new traffic signals designed to be
more cost efficient started to be introduced nationwide.

24

7. Q&A
Q1 Why is the green traffic light referred to as "blue" in Japanese?
A1

25

e

This is a commonly
asked question.

Gr
e

en

Blu

When the first traffic light was installed in Japan in
1930, the "go" light was named the "green" light underJapanese law. Even then, however, this light was
already being commonly referred to as the "blue signal
light" in newspapers and by the public. This is probably
because the three primary colors of blue, red, andyellow were easy for everyone to understand as
expressions for the colors of traffic lights. In addition,
the term "blue" in Japanese can represent a wide
range of color shades. For example, green vegetables
are often called "blue" vegetables or "blue" crops inJapanese.
As the "go" light was commonly called the "blue" light,
it was also defined as such in the laws and ordinances
enacted in 1947. However, international standards
define the colors of traffic signal lights as green, yellow,
and red.

7. Q&A

Q2 Some push-button traffic signals don't turn green immediately after
the button is pushed. Why is that?

A2

Push-button traffic signals are generally designed toturn green as soon as the button is pushed. However,imagine what would happen if a push-button signal
turned green immediately on a road where acoordinated traffic control system was being used.
Every time the button was pushed, the traffic signals
would become uncoordinated, rendering thecoordinated control system totally ineffective. To avoid
impeding the flow of vehicles that are travelinguninterrupted along highways, push-button signals aredesigned not to change even if the button is pushed if
it is during a time zone when a signal change may
result in a disruption of the traffic. This is why somepush-button signals do not turn green immediately after
the button is pushed.

A push-button signal isdesigned to change
immediately after the button
is pushed, except if…

26

7. Q&A

Q3 Why are vehicles or pedestrians sometimes kept waiting for a longtime by trafﬁc signals during the night and other quiet periods when
there are no other vehicles crossing the intersection?

A3

Push-button trafﬁc signals and semi-actuated signals
installed at intersections that are used by few vehicles
or pedestrians even during the day are set so that they
will not impede trafﬁc on the main road unnecessarily.
However, at intersections with heavy trafﬁc, the trafﬁcsignals for main and subsidiary roads are displayedalternately. Consequently, vehicles and pedestrians are
sometimes kept waiting even at night when there areno other vehicles crossing the intersection. To resolve
this issue, an increasing number of trafﬁc signals havebeen redesigned in recent years to switch to a semiactuated trafﬁc control system during hours when there
is little trafﬁc.
This should help reduce driver stress.

Irri

d
e
t
ta

27

This is really irritating
for drivers.

7. Q&A

Q4 Traffic signals are actually the cause of traffic congestion, aren't
they?

A4

It's true that there is always a traffic signal at the frontof a traffic queue. But stop to think for a moment: do
traffic signals actually cause traffic congestion? Just
imagine what would happen at busy intersections if we
didn't have traffic signals: At an intersection where
there is a clear difference in traffic volume between themain and subsidiary roads, vehicles on the main roadwould always have priority and prevent vehicles on thesubsidiary road from crossing the intersection, thereby
causing traffic congestion on the subsidiary road.
Meanwhile, at an intersection with no clear distinction
between the main and subsidiary roads, vehicles would

get in each other's way, making it difficult for them totravel smoothly. Installing traffic signals at intersections
such as these ensures a smooth flow of traffic.
However, because vehicles on the main and subsidiaryroads pass through the intersection alternately, thetraffic processing capacity decreases, which results intraffic congestion if the number of vehicles exceeds the
traffic processing capacity.
In other words, traffic congestion occurs not becauseof traffic signals, but because of the existence ofintersections.
Traffic signals help to maintain traffic order and relieve
traffic congestion by appropriately controlling the traffic.

Yes, there is always atraffic signal at the front ofa traffic queue. But justthink for a moment.

28

8. Relationship between the number of traffic signals
and the number of traffic accident deaths
In Japan, the total number of traffic accident deaths
was 16,765 in 1970, a figure that raised serious publicconcerns. With a view to halving this number, theNational Police Agency launched a five-year plan todevelop traffic safety facilities in 1971. In 1979, theagency achieved results that were close to the plan's
goal despite the fact that the number of vehicles had
doubled.
Furthermore, efforts to ensure greater traffic safety andefficiency helped shorten travel times, which in turncontributed to reduced working time and lower gasoline
and fuel costs.

No. of vehicles (B)No. of deaths fromtraffic accidents (A)No. of deaths from traffic accidents
per No. of vehicle (A/B)

70

75

80

85

90

95
Year

00

05

10

15 16

25

No. of traffic signals installed (10,000)

20

15

10

5

0

70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16
Fiscal year

Trends in the number of traffic signals

29

8. Relationship between the number of traffic signals and the number of traffic accident deaths

As this demonstrates, traffic signals have contributed
greatly to reducing the number of traffic accidents. To
prevent traffic accidents and reduce traffic congestionin accordance with changing traffic conditions, it isessential that we manage and operate traffic signals inaccordance with the conditions of individual areas.
Traffic control centers also contribute to ensuring traffic
safety and efficiency throughout Japan. In addition to
improving the performance and operation of traffic
signal control, they also collect data on traffic
conditions, including traffic congestion, and provide
such information to drivers.

札幌

青森

秋田
盛岡

Areas with traffic control centers

山形
仙台
新潟

富山
金沢
福井
鳥取

松江

広島

佐賀
長崎

福岡

大分

神戸 京都
奈良

岡山
高松

山口
松山

高知

大津

大阪
和歌山

宇都宮
長野
甲府

岐阜
名古屋

福島

静岡

水戸
前橋

さいたま
東京

横浜

千葉

津

徳島

熊本
宮崎
鹿児島

那覇

NB: Circles indicate traffic control center headquarters that are located in prefectural capitals. In addition tothese centers, there are also municipal traffic control centers. There are a total of 75 traffic control centers inJapan (as of the end of fiscal 2016).
30

9. New traffic control system
Universal Traffic Management Systems (UTMS) are designed to help realize a motorized society that is safe,
comfortable, and environmentally friendly by using infrared beacon features such as vehicle detection and two-way
communication.
The main UTMS features are as follows: responding to traffic accidents; offering support to senior citizens andphysically disabled people; reducing traffic congestion; controlling traffic pollution; supporting safe driving; andproviding comfortable mobility.

ITCS (Integrated Traffic Control Systems)

FAST (Fast Emergency Vehicle
Preemption Systems)

Fast Emergency Vehicle Preemption Systems areintended to assist emergency vehicles to reach an
accident site as quickly as possible and prevent
secondary accidents caused by emergency
vehicles. Based on the information received fromemergency vehicles via infrared beacons, theTraffic Control Center extends the green or
shortens the red light so that emergency vehicles
can arrive at the scene of accidents faster.

HELP (Help system for
Emergency Life saving andPublic safety)

In the case of an emergency while driving,such as traffic accidents, Help system for
Emergency Life saving and Public safety
reports the accident to the police andemergency services via the operation
center, notifying them of the accurate
location of the vehicle and the circumstances of the accident.

Integrated Traffic Control Systems are the key components of UTMS,
which collect traffic information using ultrasonic sensors, image
processing detectors and infrared beacons. Based on the informationcollected, ITCS provides optimal signal control (green time allocation
based on traffic volume, decision on the timing of green light in orderto decrease the number of vehicle stops at intersections) and
implements advanced functions of each subsystem of UTMS.

Idling s

TSPS (Traffic Signal Prediction
Systems)

Traffic Signal Prediction Systems encourage safe andeco-friendly driving by providing drivers with driving
support information based on information about thecolor of traffic lights.
Typical support includes the following:- Signal passing support- Signal stopping support- Idling stop support- Signal change starting support

Signal stopping support
Signal passing support

AMIS (AdPTPS (Public Transportation
Priority Systems)

Public Transportation Priority Systems ensure thescheduled operation of buses and other public
transport and encourage the use of public transport.
Based on vehicle ID information received from theon-board unit in the bus via infrared beacons, theTraffic Control Center extends the green or shortens
the red light so that buses can pass intersections
smoothly. There is a case in which the implementationof PTPS reduced bus operational hours by 13%.

EPMS (Environmental Protection Management Systems)

Advanced Mo
congestion an
the Traffic Co
drivers via VIC
information dis

Stop sign r

Environment Protection Management Systems are intended to reduce traffic pollution
such as air pollution and noise to protect the environment. Exhaust gas detectors andnoise detectors installed on roadsides collect environmental information, while
infrared beacons collect traffic information. Based on the information, such as
exhaust gas concentration, EPMS limit the inflow of vehicles and provide alternativeroute guidance via traffic information display boards and infrared beacons.

止
まれ
Crossing collision prevention system

Rear-end co31

9. New traffic control system

Systems)

nents of UTMS,
sensors, image
the informationn time allocationen light in orderersections) andUTMS.

Signal change starting support

PICS (Pedestrian Information and Communication
Systems)

Pedestrian Information and Communication Systems facilitate safe crossing ofintersections by pedestrians including the elderly and people with disabilities by
providing information by voice, on the name of intersection and the pedestriansignal status. There are two versions, one using a hands-free terminal carriedby pedestrians and the other using a long cane with a reflective sheet which isdetected by roadside sensors.

Idling stop support

ng support

Right-turn collision prevention system

Crossing pedestrians recognition enhancement system
Crossing bicycle collision prevention system

Left-turn collision prevention system
Stop sign recognition enhancement system
Signal recognition enhancement system

DSSS (Driving Safety Support Systems)止まれn system

AMIS (Advanced Mobile Information Systems)

Advanced Mobile Information Systems generate information oncongestion and travel time, based on traffic information collected at
the Traffic Control Center and provide that information to generaldrivers via VICS. The information is also provided by roadside traffic
information display boards as well as by radio broadcast.

Driving Safety Support Systems grasp traffic situations of anarea which is hard to see from driver’s position using roadside
sensors and alert drivers via on-board units and thereby prevent
traffic accidents caused by careless oversight such as inattentive
driving. DSSS consist of the following eight subsystems:- Rear-end collision prevention system- Crossing collision prevention system- Signal recognition enhancement system- Left-turn collision prevention system- Right-turn collision prevention system- Crossing pedestrians recognition enhancement system- Stop sign recognition enhancement system- Crossing bicycle collision prevention system

Rear-end collision prevention system

MOCS (Mobile Operation Control
Systems)

Mobile Operation Control Systems help bus and truck operators accurately identify the status of their vehicle operationand increase the efficiency of the flow of people and goods.
Vehicles and vehicle operators can send and receive
information via infrared beacons and the Traffic Control
Center, allowing efficient management of vehicle operation.

32

Part II (an in-depth study of traffic signals)

1. Signal phase

⿓Standard two-phase control system

Let's consider how traffic is controlled at a crossroadintersection.
At an intersection where few vehicles turn right or left,
the signals for the main and subsidiary roads operate
in alternate signal phases. The figure on the rightshows a standard arrangement of traffic signal lights at
a crossroad intersection. Signals (A) and (B) are
vehicle traffic signals and signals (AP) and (BP) arepedestrian signals. Signals (A) and (AP) operateaccording to the signal phases for the main road while
signals (B) and (BP) operate according to those for thesubsidiary road.
The timing for a switch in the signal displays is called a"step." The 2-phase 10-step traffic signal system ismost commonly used. A signal phase table such as theone shown below is used to represent the display
switch timings.
Step

1

2

3

4

5

6

Arrangement of traffic signals

7

8

9

10

Main road pedestrian signal (AP)Main road vehicle signal (A)Subsidiary road pedestrian signal (BP)Subsidiary road vehicle signal (B)Duration in seconds
Signal phase

45

5

5

3

2

25

①

5

5

3

2

Green signal for vehicles and pedestrians
Yellow signal for vehicles
Red signal for vehicles and pedestrians
Flashing signal for pedestrians②

Pedestrian flow
Traffic flow
Vehicle flow

Signal phase table (example)

33

1. Signal phase

⿓Right-turn phase

Next, let's consider how traffic is controlled at anintersection where many vehicles turn right.
If there is too much oncoming traffic for vehicles to turnright when the light is green, many vehicles will remainin the intersection, thereby obstructing the next
vehicles to enter the intersection and causing traffic
congestion.
Installing an arrow traffic signal for right-turning
vehicles enables them to pass through the intersection
more efficiently and helps reduce traffic congestion forright-turning vehicles. The arrow signal also separates
the flow of vehicles turning right from that of vehicles
going straight ahead and helps prevent accidents
involving these vehicles.
To this end, a signal phase for right-turning vehicles is
added to the standard two-phase signal control system
to create a three-phase one.
As the above indicates, many different types of phase
control systems are designed for intersections basedo n t h e t r a ff i c c o n d i t i o n s a n d s h a p e s o f t h eintersections.
①●Standard two-phase signal control Signal phase②

Traffic flow

●Three-phase signal control Signal phase

①

②

③

Traffic flow
Right-turn phase34

1. Signal phase

⿓Deductible phase signal control system

A deductible phase signal control system is designed
to turn off the green light at a T-junction or crossroadintersection earlier for one of the two traffic flows
controlled during one signal phase and extend thegreen light time for the other in order to separate
vehicles turning right from those going straight ahead.

35●Deductible phase signal control system
Signal phase

Traffic flow

①

②

③

1. Signal phase

⿓Separate phase signal control system

This system combines green arrow signals for vehicles
going straight ahead, vehicles turning right, andvehicles turning left rather than having a single green
light signal. It is implemented in situations such as
when it is necessary to separate the flows of vehicles
turning right and left from the flow of vehicles goingstraight ahead. Since this system controls signals toseparate traffic flows, it is called a separate phasesignal control system.
①●Separate phase signal control system②③④

Traffic flow

②

Red

①

Signal phase

Red

Red

Red

Red

Red
Red

③

Red

④

Red
Red

Red

Red
Red

Red
Red

Red

36

2. Types of signal control systems(1) Traffic-actuated control system
⿓Multistage control system

The traffic volume changes depending on whether it ismorning, afternoon, or evening as well as whether it isa weekday, weekend, or public holiday. If the green
light time was always the same despite such changes
in traffic volume, the traffic control would be inefficient.
Given this, a survey on traffic volume was conductedwith the aim of developing a traffic signal control
system designed to optimize the green light time fordifferent times and days of the week. This system iscalled a multistage signal control system. By using abuilt-in electronic time switch, the system automatically

identifies the current time and day of the week andthen chooses the appropriate signal pattern for traffic
control from among the pre-registered control patterns.
The multistage control system is suited to intersections
where the traffic volume remains roughly the same
during specific hours and on specific days of the week.

Today is a public
holiday. We need toincrease the green lighttime on main roads thatlead to holiday resorts.

Traffic volume

Signal controller

Congestedtraffic pattern

Low traffic
pattern

Congestedtraffic pattern
Normaltraffic pattern

Normaltraffic pattern

Normaltraffic pattern

Time

Multistage signal control system
37

Microcomputer

Low traffic
pattern2. Types of signal control systems

⿓Push-button-actuated control systemchanges the pedestrian signal to green only when apedestrian wanting to cross the road pushes the button
mounted on the signal pole. The vehicle signal remains
green unless the button is pushed.

What would happen if we installed the type of traffic
signal used for an intersection at a pedestriancrossing? The signal would enable pedestrians tocross the crossing safely, but they would have to wait
until the signal turned green even if there were novehicles on the road.
Meanwhile, vehicles would also be kept waiting when
the signal turned red even if no pedestrians werecrossing the road, which would result in reduced traffic
efficiency. A push-button-actuated signal controller wasdeveloped to avoid such difficulties. The controller

Vehicle signal

Pedestrian signal
Signal controller

Push-button box■ State A: The button has not been pushed.
⃝ Vehicle signal: Green⃝ Pedestrian signal: Red■ State B: The button is pushed.

⃝ Vehicle signal: Changes from green to yellow to red⃝ Pedestrian signal: Changes from red to green

38

2. Types of signal control systems

⿓Traffic-actuated signal control system

Although a multistage signal control system offers anefficient means of controlling traffic when the volume
changes according to nearly the same pattern, it
cannot efficiently control traffic that changes according
to unpredictable patterns. The traffic-actuated signal
control system was developed to allow more detailed
traffic control than is possible with multistage control bydetermining the green light time based on the actual
traffic volume. A traffic-actuated signal control system
calculates the green light time in accordance with the Push-button box
traffic volume by using vehicle detectors.

Vehicle traffic signal
Pedestrian traffic signal
Vehicle traffic signal

Main road

Vehicle detector(a) Semi-actuated signal control system
With a semi-actuated signal control system, the signal
on the main road always remains green unlessvehicles or pedestrians are detected on the subsidiaryroad, at which point the signal on the subsidiary roadturns green. This type of system is suited tointersections that have a relatively low volume of traffic
on the subsidiary road.
(b) Fully actuated signal control system
Unlike a semi-actuated signal control system, which
controls signals by means of vehicle detectors installed
only on the subsidiary roads, a fully actuated signal
control system controls the green signal time for boththe main and subsidiary roads based on the traffic
volume measured by means of vehicle detectors
installed in all directions, including on the main roads.
This type of system is suited to intersections that havea traffic volume that changes rapidly according tounpredictable patterns.

■ State A: The push-button has not been pushed or
no vehicle has been detected.
⃝ Vehicle traffic signal (on main road): Green⃝ Vehicle traffic signal (on subsidiary road): Red⃝ Pedestrian traffic signal (on subsidiary road): Red■ State B: The push-button is pushed or vehicles
are detected.
⃝ Vehicle traffic signal (on main road): Changes fromgreen to yellow to red⃝ Vehicle traffic signal (on subsidiary road): Changes from
red to green⃝ Pedestrian traffic signal (on subsidiary road): Changes
from red to green
Vehicle traffic signal

Vehicle detector

主道路
Main road

39

Vehicle detector

2. Types of signal control systems(c) Right-turn-actuated signal control system
Let's suppose that the green signal time for rightturning vehicles is always the same at an intersection
where many vehicles turn right and the traffic volume
varies considerably depending on the time. At such anintersection, a large number of right-turning vehicles
would sometimes be kept waiting, thereby causing
traffic congestion. Also, the green signal time for rightturning vehicles would often be wasted. To avoid this,traffic is controlled by changing the signal time for theright-turn arrow in accordance with the volume of rightturning traffic by using vehicle detectors installed on
the right-turning lanes. This system is called a rightturn-actuated signal control system. This systemenables right-turning vehicles to travel safely while also
improving the traffic processing capacity ofintersections.
(d) Low-traffic semi-actuated signal control system
Vehicles are sometimes kept waiting for a long time ata red light during the night and other quiet periods
when there are no other vehicles or pedestrians
crossing the intersection. A low-traffic semi-actuatedsignal control system was developed to eliminate such
inefficiencies. This system carries out ordinary signal
control during the day when there is heavy traffic, andthen carries out semi-actuated signal control during the
Vehicle detectornight and other periods of low traffic to give priority tomain road traffic. As such, this system is suited tointersections where the traffic volume during periods of
low traffic is significantly less than that during the day.

Vehicle traffic signal
Vehicle traffic signal

Right-turning
vehicles

Vehicle detector

Vehicle traffic signal
Pedestrian traffic signal
Signalcontroller

402. Types of signal control systems(e) Speed-actuated signal control system
A speed-actuated signal control system controls traffic
signals by using the traffic speed data obtained from avehicle detector installed just before an intersection tomeasure traffic speed. When the system detects avehicle traveling at excessive speed, it reduces thegreen signal time at the downstream intersection if thesignal there is green and increases the red signal time
if the signal is red in order to effectively stop thevehicle.
Vehicle detector

Speed warning sign

Traffic signal

Intersection

Speed-actuated control is actually similar to dilemmazone avoidance control, which aims to prevent the riskof collisions immediately after a yellow signal as wellas head-on collisions caused by vehicles entering anintersection when the signal is red. Dilemma-zone
avoidance control determines whether a green signal
should be continued or terminated by detecting
vehicles that are hesitating about whether to stop
before the intersection or pass through it.

41

Note
Pedestrian-friendly signal control systems
⿓Elderly-actuated signal control system

An elderly-actuated signal control system isimplemented at intersections where senior citizens andphysically disabled people often cross. It enables
pedestrians to extend the pedestrian green signal timeby pushing a button or by operating a portabletransmitter.

⿓Traffic signals for the visually impaired

A traffic signal designed mainly for the visually impaired
informs pedestrians that the pedestrian signal iscurrently green or has turned green by means of asound, such as a melody (Toryanse or Kokyo no Sora)or an artificially created bird sound ("cheep-cheep" or"coo-coo").

Bird'ssong

⿓Pedestrian wait-time displays

A pedestrian wait-time display is designed to indicate
to pedestrians how much longer they will have to wait
before the pedestrian signal turns green and how muchtime remains before the pedestrian green light starts
blinking.

⿓Pedestrian-vehicle separation signals

A pedestrian-vehicle separation signal is designed toprevent traffic accidents involving pedestrians andvehicles by separating the crossing times forpedestrians and those for vehicles at intersections
where pedestrians and vehicles may otherwise collidewith each other and cause accidents.

Standard pedestrian-vehicle separation signals

42

2. Types of signal control systems(2) Coordinated signal control system

Next, let's consider how traffic is controlled on a trafficroute to ensure a smooth flow of traffic throughout theentire route.
What would happen if each traffic signal operated
separately on a route where traffic signals were installed
consecutively? Vehicles would be stopped at each red
light, which would just waste time and cause traffic
congestion. Developed to reduce such congestion, theline traffic control system is designed to coordinate theoperations of traffic signals that are installed
consecutively to ensure a smooth flow of traffic.
With this system, the traffic signals must operate withthe same cycle length and the signals must be
coordinated by adjustment of the offsets.
The light has
turned green!

All of the lights turngreen in sequence.

I passed throughall of the signals
without having to stop!

43

2. Types of signal control systems

⿓Implementing line traffic control

Line traffic control is used to coordinate adjacent traffic
signals by adjusting the offsets so that vehicles cancross intersections smoothly without having to stop at
the signals.
Take a look at the figure on the right.
Having passed through intersection A, vehicle a wasable to pass through all of the subsequent intersections(B, C, and D) at a constant speed without having tostop because the traffic lights turn green at theseintersections according to a regular sequence.
However, vehicle b increased its speed so it had tostop at intersections B and D. Vehicles a and b—bothof which left intersection A at the same time—passthrough intersection D at the same time. In otherwords, the travel time of a vehicle that travels at a highspeed is no different to that of a vehicle that travels
more slowly at a constant speed.
As this example shows, offsets not only allow vehicles
traveling at a constant speed to travel safely andsmoothly without having to stop at red lights, but also
provide an effective means of preventing vehicles fromtraveling at an excessive speed.
However, offsets are not always adjusted to enable
vehicles to pass through all of the intersections without
having to stop. For example, even on roads that havenearly the same traffic volume on their upstream anddownstream lanes under normal conditions, the volumeof upstream traffic may exceed that of downstream
traffic during the morning rush hour. In such cases, theExamples of offsets
Time

Dow

nstr

eam

m

trea

Ups
b

a
…
スイ
スイ

Intersection

Intersection A

A

B

B

C

C

D DistanceD

upstream traffic is prioritized, resulting in vehicles
traveling downstream being unable to travel without
having to stop. The offsets are adjusted according to
the current traffic conditions.

44

2. Types of signal control systems

⿓Multistage coordinated signal control

Multistage signal control, which was mentioned in thesection on point traffic control, can be used in
combination with coordinated signal control. Multistage
coordinated control is implemented to control traffic byusing different signal patters based on the time of day(e.g., three patterns for heavy traffic periods, normal
traffic periods, and low traffic periods). This system ismost effective on roads where there is a relatively
constant volume of traffic with a clear pattern ofchange.

⿓Line-coordinated automatic traffic signal control

On roads where the traffic flows are constantly
changing, a traffic control system that is capable ofresponding to changes in traffic is required. A linecoordinated automatic traffic signal control system issuited to such roads. This system is composed of thefollowing: a central computer that determines the cycle
lengths, the splits, and the offsets; vehicle detectorsthat collect traffic volume data and other traffic
information; and traffic signals. The central computer
and the traffic signals are connected via
communication lines so that they can exchange
information.

Instruction to change thetraffic signals
Vehicle detector information

The central computer collects traffic volume data andother information from vehicle detectors installed along
the roads and controls the individual traffic signals byautomatically selecting the appropriate pattern from thevarious pre-registered patterns in accordance with thetraffic conditions.

45

2. Types of signal control systems(3) Area traffic control system

Next, let's consider how traffic can be efficiently
controlled in an area where many traffic signals havebeen installed. Metropolitan cities are covered withcomplex networks of busy highways as well as smaller
roads that are used by many vehicles and pedestrians.
In such areas, a large number of traffic signals are
installed to prevent accidents and to create a smooth
flow of traffic. If these traffic signals operated
independently of each other, urban traffic would bethrown into chaos. Furthermore, controlling urban
traffic with line control systems does not improve thetraffic flows on subsidiary roads that intersect
highways. To efficiently control traffic in urban areasthat have a complex network of roads, it is necessary
to implement area traffic control. An area traffic control
system controls individual traffic signals by using thecomputers in traffic control centers.

Traffic control center46

2. Types of signal control systems

⿓Flowchart of area traffic control

An area traffic control system controls individual traffic
signals according to the procedure shown below.

Traffic control center

Vehicles detected

Traffic volume or traffic
congestion calculated

Optimal cycle lengths, splits,
and offsets selected

Traffic signals displayed

47

Signal display instructions issued

2. Types of signal control systems

⿓Implementing area traffic control

Various types of districts can be found in urban areas.
These include districts where traffic becomescongested during the morning and evening commuting
hours, downtown districts where there are many
pedestrians, and districts where there is heavy leisuretraffic on weekends and public holidays. These traffic
conditions vary widely depending on the characteristicsof the individual districts. Controlling a group of urban
traffic signals with the same control patterns (i.e., thecombination of cycle lengths, splits, and offsets)
without regard for these differences can cause
problems, such as traffic congestion in some districts
due to an excessively short green light time or
increased signal wait time and frequency in others due
to wasted green light time.

Commuter town

Office district
Resort district

To eliminate such inefficiencies, small groups ofintersections that have similar traffic conditions (called"sub-areas") are chosen and appropriate control
patterns are selected for them in accordance with theirrespective traffic conditions. Furthermore, if adjacentsub-areas have similar traffic conditions, they too aregrouped together to implement traffic control.
Combining and separating sub-areas in accordancewith the traffic conditions in order to form groups thatare optimized for signal control enables complex
vehicle flows to be controlled throughout the entire
area.

Residential district48

2. Types of signal control systems(a) Combining and separating districts
In urban districts that have different traffic conditions—such as residential districts, office districts, and resort
districts—the traffic signals are usually controlled inaccordance with the conditions of the respective
districts. However, if the traffic volume between specificdistricts increases, sub-areas are combined to form alarger area that is separated from other districts thathave a lower traffic volume so as to automatically form
optimal areas for signal control.
Take a look at the figures on the right.
As these figures illustrate, an area is formed during themorning and evening rush hours to link the residential
district and the office district, thereby helping to createa smooth flow of commuter traffic. On weekends,
however, a different area is formed to link theresidential district to the resort district. In this way,
areas are formed depending on the time of day and the
day of the week to appropriately control traffic. Forming
areas in accordance with the different conditions
facilitates more detailed traffic control.

Bedroom town

Office district

Commuter town
How districts are linked during the morningand evening rush hours
Bedroom town(b) Area traffic control based on traffic conditions
Based on traffic volume and other data collected by
vehicle detectors, control patterns are selected foreach individual area and traffic control is thencoordinated among these areas by calculating the
optimal control parameters for the current traffic
conditions.
In recent years, systems have also been developedthat predict traffic congestion in advance based on pastdata and then reflect these predicted results in traffic
control to minimize traffic congestion.
As these examples show, area traffic control has been
implemented in suburban areas where there are many
traffic signals, thereby achieving significant results.

49

Resort district

Commuter town
How districts are linked on weekends

2. Types of signal control systems

⿓High-performance area-signal control system

The traffic conditions at key urban intersections canchange rapidly, so pre-registered signal patterns are
not always efficient enough to provide detailed control
in response to the changing traffic conditions. New
signal control systems have been developed to deliver
more advanced and sophisticated signal control forthese key urban intersections.
(a) MODERATO signal control system
A MODERATO signal control system calculates
the optimal green signal time in units ofseconds based on traffic flow measurements.
This system forecasts the traffic demand for
different travel directions from detector data on
the traffic volume and the congestion length forthe past 5 minutes (or in some cases 2.5
minutes or 1 minute) and then calculates thenecessary green signal time.
The system calculates the necessary green
signal time in units of seconds without being
restricted by the need to selectsignal patterns. This facilitatesdetailed signal control even at key
urban intersections where the traffic
conditions can change rapidly.
(b) Profile signal control system
In ordinary area control, traffic
control centers select the control
patterns based on the traffic flow
measurements for the past 5
minutes (or in some cases 2.5
minutes or 1 minute). This causes
a delay of several minutes before
the measurements are reflected in
the traffic control. To eliminate this
delay, a profile signal control
system calculates the optimal
cycle lengths and splits by

predicting what the traffic flow pattern will be at anintersection when the traffic flow measured upstream
reaches it.
A profile signal control system exchanges traffic flow
measurement data between the signal controllers
installed at different intersections and allows thesecontrollers to calculate the cycle lengths and splits
independently without the help of traffic control centers.
In light of this, a profile signal controller is also
sometimes referred to as a thinking signal controller. It
prevents delays in control, thereby resolving an issue
associated with area signal control.

How the profile signal control system works
Calculates cycle lengths andsplits for future traffic flow
patterns A and B and issues
control instructions

Sends traffic flow
patterns A and B

Sends traffic flow
pattern B

Detects smooth traffic(pattern A)

Traffic control center
Detects traffic congestion(pattern B)

・Monitors abnormal signal control operations
・Provides instructions to intervene in signal control

50

3. Structure of traffic signals
A traffic signal is composed of the devices shown
below.

Green Yellow Red

Signal controller

Signal lights
Red
Green

Push-button box

Vehicle detector(1) Signal controllers

A signal controller is the brain of a traffic signal. It
measures the signal display time for the green, yellow,
and red signal lights, switches displays, changes
signals, and extends or shortens the signal display
time in response to signals from the vehicle detectors
and the push-button boxes. A signal controller for
centralized signal control also exchanges information
with traffic control centers.
Traffic-actuatedcontrol

Signal controller for
multistage control

Signal controller for
push-button-actuated control

Signal controller for
traffic-actuated control

Traffic signal
controller
Coordinatedcontrol

Area control

51

Signal controller for
multistage coordinated control
Line-coordinated automatic
traffic signal control

Signal controller for
centralized control

3. Structure of traffic signals(2) Signal lights

Traffic signals display green, yellow, and red lights.
There are two types of traffic signals: one type forvehicles and the other for pedestrians.
The lenses for vehicle signal lights are 20 to 45 cm indiameter, with the most commonly used size having a
diameter of 25 and 30 cm. Square lenses with eachside measuring between 20 and 25 cm in length areused for pedestrian signal lights. Lenses with 25-cm
sides are the most commonly used type.
Improvements to traffic signal lights are made every
year. One example of an improvement made in recent
years is the development of LED signal lights that use
LEDs as their light source.
One advantage of LED signal lights is that sunlightreflected by their interiors does not make it appear as if
they are lit. They are also more clearly visible thanbulb-type signal lights.
In addition, LED signal lights consume less electricity
and offer an effective means of reducing carbon
emissions.

Vehicle signal lights(Bulb-type)(LED-type)
Pedestrian signal lights(3) Push-button boxes

A push-button box allows pedestrians and cyclists
wishing to cross a road to change the traffic signal
situated on the other side of the road to green.

Messagedisplay
Push-button
Fixed message plate
Message display

Push-button for continuous
control system

Push-button for low-traffic semi-actuatedsignal control system
A push-button for low-traffic semi-actuated signal
control system is used in situations such as when
push-button-actuated signal control is implemented
only at night. The message "Push button" is not
displayed when push-button-actuated control is not
activated.

52

3. Structure of traffic signals(4) Vehicle detectors

Many different types of vehicle detectors are available,
including ultrasonic detectors, loop detectors, andimage-sensing detectors. The most commonly used
type is ultrasonic vehicle detectors, which are
indispensable in traffic-actuated control, linecoordinated automatic traffic control, and area control.

⿓Ultrasonic vehicle detectors

An ultrasonic vehicle detector is composed of an
ultrasonic wave transmitter/receiver called a "head"
and a main unit. This type of detector emits ultrasonicwaves toward the ground and detects vehicles byusing the main unit to measure the amount of time ittakes for the waves to be reflected back. The head isusually installed perpendicularly to the road surface ata height of approximately 5 m.

Head
Main unit

Head

Main unit

53

約 55
mm
Approx.

3. Structure of traffic signals

⿓Image-sensing vehicle detectors

An image-sensing vehicle detector is composed of a
CCTV camera and a main unit. The detector records
vehicles with its CCTV camera to detect vehicles,
count their numbers, and measure the traffic speed byprocessing the video footage. Installed directly above avehicle lane or alongside the road, an image-sensing
detector is capable of measuring vehicles traveling on
multiple lanes with a single CCTV camera.

CCTV camera
Main unit

⿓Far infrared vehicle detectors

A far infrared vehicle detector detects vehicles basedon the temperature difference between passing
vehicles and the road surface by using a far infrared(temperature) sensor.
A far infrared detector consumes little electricity. Its
sensor is installed diagonally above the traffic lane,
which allows a shorter attachment arm to be used.

SensorSensorMain unit54

3. Structure of traffic signals

⿓Infrared beacons

An infrared beacon is composed of an IR transmitter/receiver unit and a main unit. In addition to detecting
vehicles traveling on roads through the use of light(near infrared rays), it also provides traffic data via twoway communication between the vehicles and roadsideunits.

⿓High-performance infrared beacons

As well as performing the conventional functions ofcounting the number of vehicles and measuring thetravel time between infrared beacons, a highperformance infrared beacon also collects probe dataon the travel trajectory between high-performance
infrared beacons.

IR transmitter/receiver unit

Main unit

In-vehicle communication unit

Communication area

Sensing area55

4. Comprehensive checklist for traffic signals
There are a number of reasons why it is essential to
pay careful attention to traffic signals: to prevent
unexpected accidents, to ensure the safety of local
community residents, senior citizens, and the visually
impaired, and to create a smooth flow of traffic.

Checking traffic signal lights
⿓Check 1

Check that the traffic signal lights are not hidden bytrees, advertisements, or other obstacles.

⿓Check 2

Check that there are no curves or slopes with poor
visibility that require the installation of traffic signal
lights.
Require the installation of
traffic signal lights.

⿓Check 3

Check that the signal arm is not bent and that thesignal lights are not damaged or broken.

56

4. Comprehensive checklist for traffic signals

Checking signal controllers
⿓Check 1

Check that the push-button for pedestrians isfunctioning properly and that the push-button box is notdamaged or broken.

⿓Check 3

Check that the traffic signal controller is not installed ina location where it may obstruct the passage ofpedestrians due to changes in the traffic conditions.

57

⿓Check 2

Check that the signal control cover is tightly closed andthat the attachment pipes and wires are not damaged
or loose.

4. Comprehensive checklist for traffic signals

Checking vehicle detectors
⿓Check 1

Check that the head of the detector is properly
positioned (i.e., above the center of the traffic lane). If
the head is positioned incorrectly due to roadworks or
the repainting of lane markings, the detector will be
unable to detect traffic accurately and control the traffic
properly.

⿓Check 2

Check that the detector attachment arm is not bent or
damaged.

⿓Check 3

Check that no vehicles are parked under the detector
head for a prolonged period of time. Vehicles parked
there would not only obstruct traffic, but also make it
difficult to accurately measure the traffic volume.

58

4. Comprehensive checklist for traffic signals

Checking traffic congestion
⿓Check 1

Check that there is no traffic congestion in any specificdirection during the morning or evening, on specificdays of the week, or in specific seasons.

⿓Check 2

Check that traffic congestion is not being caused by
too many right-turning vehicles.

⿓Check 3

Check that traffic congestion is not being caused by too
many pedestrians crossing the intersection, thereby
causing left-turning vehicles to have to wait for a long time.

59

MEMO

Published by Japan Traffic Management Technology Association
T E L：+81-3-3260-3621
FAX：+81-3-3260-3892
URL：https://www.tmt.or.jp/
Printed in JAPAN2018.2/ 改編
定価（本体 270 円 + 税）