Technology

Technology

Railway Technology Today 8 (Edited by Kanji Wako)

Signalling Systems for Safe Railway Transport
Tetsuo Takashige
blocks and to control the signals for eachblock. All double-tracked sections in Japanuse the automatic block system. As
Figure 2a shows, there are basically threesignal aspects: red, meaning stop
immediately before entering the next
track section occupied by an ahead train;yellow, meaning proceed with caution at
a speed no greater than 45 km/h (55 km/h
or faster is permitted on some sections) as
far as the signal, and green, meaning thenext track section is clear and the train
can enter that section at the maximum
speed. In heavily used sections, two othersignal aspects are also used (Fig. 2b): twoyellow lights (restricted speed), and one
yellow and one green light (reduced
speed).

applied—is longer for trains than it is forroad vehicles. Consequently, only one
train can occupy a specific section of trackat one time. Such a section of track iscalled a block. Track circuits are used todetermine whether a train is in a specificblock.
Figure 1 shows how the rails form part ofan electric circuit (track circuit). Whenthe train’s wheels pass a certain point, theycause a short circuit, preventing electric
current from proceeding further. This
makes it possible to detect a train in a
block.
An automatic block system uses the track
circuit to automatically detect trains in

Introduction

Trains could not run safely without
signalling devices. This article looks atfour tools that ensure railway safety inJapan: block systems, train control systems,
train traffic control systems, and wirelesscommunications devices.

Block Systems

Automatic block system
Braking distance—the distance needed tocome to a complete halt after brakes are

Figure 1 General Principles of Track Circuit

Other block systems

Train wheels short-circuit passage
of current to receiver

In addition to the automatic block system,
a number of other block systems are usedon single tracks. In many cases, a track
circuit system or an electronic block
system (electronic coding verification
system) is used. Both are semi-automatic
block systems.
The track circuit system controls train
movement in the blocks between stations,and involves interlocking signal levers at

TrainTransmitter

ReceiverActivated relay released
by train short-circuiting rails

Figure 2 Automatic Block Signalling System(a) Normal track section
STOP

CAUTION

CLEAR

G Y R

G Y R

G Y R

R : RedY : Yellow
G : Green

T : Transmitter (power supply)
R : Receiver (track relay)
R

T

R

T

R

T

R

T

Signal current cut(b) High-density traffic
track section

R

44

T

STOP

RESTRICTED SPEEDCAUTION

REDUCED SPEEDCLEAR

Y Y R Y GY Y R Y GY Y R Y GY Y R Y GY Y R Y GR

TJapan Railway & Transport Review 21 • September 1999

R

T

R

T

R

T

R

T

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Figure 3 Operation of ATS-S System

Alarm
rings

Emergency brakes automatically applied
to stop train if driver fails to brakewithin 5 seconds
5-second intervalTrain speed
Pattern followed when driver brakes to stop
STOP signal
Ahead train
Alarm rings here

Alarm distance(emergency braking distance + safety margin)
STOP signal

White light ON
STOP signal
Red light ON, bell rings

Alarm
rings

When driver brakes
within 5 seconds to stop

STOP signal

White light ON, chime rings
5-second interval
If driver does not brakewithin 5 seconds to stop

White light ON, chime rings
Train stops

Red light ON, bell rings

the two stations that a train is travelling
between. The train’s departure and arrival
are detected by the track circuits at thestation entrance and exit.
In the electronic block system, each train
has a radio communications device thattransmits the train’s ID. When the driver isready to leave a station, he presses abutton and the signal changes automaticallyto green. When the train arrives at thenext station, the train’s ID is transmitted
to a receiver, clearing the block. This typeof electronic block system requires fewer
staff because the driver basically controls
the block.

Train Control Systems
Automatic Train Stop (ATS)The driver must always obey the signal,
but the possibility of human error cancause serious accidents. Two rail accidents

STOP signal

Emergency
brakes applied
Red light ON, bell rings

with serious loss of life in the early 1960s
resulted in the installation of the so-called
Automatic Train Stop (ATS) systemthroughout Japan. In the ATS system, an
alarm sounds in the cab when the train
approaches a stop signal, warning thedriver to stop. If he fails to apply the brakes,
the ATS stops the train automatically.
(Figure 3 shows the operation of the ATS-S
system used by the JRs.)
The ATS system uses ground coils
installed on the track some distance before
signals. If a train passes a coil when thesignal aspect is stop, an alarm is sent
immediately to the driver, regardless ofthe train speed. If the driver does notstop within 5 seconds after the alarm isreceived, the emergency brakes are applied
automatically to stop the train. In otherwords, the emergency brakes are notapplied if the driver applies the brakes
and presses the Acknowledge button.
However, this means that if the driver

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stops at the ground coil, the train can stillproceed under his control through a stop
signal. So-called 'absolute stop' groundcoils that do not depend on driverackowledgement are installed in stations
and at start signals to prevent any possibilityof an accident occurring due to the driver
moving ahead by mistake.
A new ATS-P type of system that does notdepend on driver acknowledgement has
been installed recently, mostly in theTokyo and Osaka regions. Ground coils
communicate between the ground andthe trains (Fig. 4) and train braking patterns
are monitored by the ground coils toensure that the trains stop before a stop
signal. If a train exceeds the speed
permitted by the braking pattern, theservice brakes are applied automaticallyto stop the train. The train can thenproceed again, but only in accordancewith instructions received from the next
coil. This system offers higher safety

Japan Railway & Transport Review 21 • September 1999

45

Technology

levels, because it does not depend on
driver acknowledgement.
Private railways in Japan have installed
an improved version of the ATS-S systemthroughout most of their networks. Thissystem offers on-board speed verification
capability and, since it can apply train
brakes automatically, does not depend on
driver acknowledgement.
In an intermittent control system using
coils, no information is received before
the train passes the coil, meaning thatsignal changes in heavily used sections
do not provide a suitable level ofcompliance. To alleviate this problem,
the railways have installed a continuous
control ATS system for some track sections.
This system uses an audio-frequency (AF)current to transmit ATS-related information
along the track circuit, making it possible
to receive information on board the train
at any time. This system offers similaradvantages to the ATC system described
below.

Automatic Train Control (ATC)Automatic Train Operation (ATO) system
can automatically control departure fromstations, the speed between stations, andthe stop position in stations. It has been
installed in some subways.

The Automatic Train Control (ATC) system
was developed for high-speed trains likethe shinkansen, which travel so fast that thedriver has almost no time to acknowledge
trackside signals. The ATC system sends
AF signals carrying information about the
speed limit for the specific track section
along the track circuit (Fig. 5). Whenthese signals are received on board, thetrain’s current speed is compared with the
speed limit and the brakes are applied
automatically if the train is travelling too
fast. The brakes are released as soon as
the train slows below the speed limit.
This system offers a higher degree ofsafety, preventing collisions that might becaused by driver error, so it has also been
installed in heavily used lines, such as
Tokyo's Yamanote Line and some subway
lines.
Although the ATC applies the brakes
automatically when the train speed
exceeds the speed limit, it cannot control
the motor power or train stop position
when pulling into stations. However, theDigital ATC
The ATC system has been used to control
all sections of shinkansen tracks ever since
the first shinkansen in 1964 and there has
never been a collision. However, ATC has
three disadvantages. First, the headway
cannot be reduced due to the idle running
time between releasing the brakes at one
speed limit and applying the brakes at thenext slower speed limit. Second, thebrakes are applied when the train achieves
maximum speed, meaning reduced ride
comfort. Third, if the operator wants to
run faster trains on the line, all the related
relevant wayside and on-board equipment
must be changed first.
The digital ATC system uses the track circuits
to detect the presence of a train in thesection and then transmits digital datafrom wayside equipment to the train on

Figure 4 Operation of ATS-P System

Braking pattern createdTransceiver
Receive
logic
unit

Speed
check
unit

RecorderBrakecommandControllerBrakemechanism

On-board transponder

TG

No. 3
Repeater

Signal aspect and distanceto stop signal
Electrical signal

Ground coils
at 650 m

Passive ground coils(two in unit)

Braking pattern

No. 2
Repeater
Data circuit (1 pair)Ground coils
at 180 m
No. 1
Repeater

Ground coils
at 30 mSignal aspect data
Codeprocessor

Power supply circuit (1 pair)To central monitoring equipment(system supervision)

TG: Tachometer generator

46

Japan Railway & Transport Review 21 • September 1999

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Figure 6 Digital ATC Train Running PatternFigure 5 ATC Train Running PatternLight braking force at first
300

300

275

275
230

Running pattern

ATC Signals
170
120

Train speed(km/h)

Train speed(km/h)

230

Braking pattern
170

Lighter braking
120

Emergency
braking

70

70

30

30

0

Full service braking
Running pattern

Alarm

0
300

275

230

170

4

30

the track circuit numbers, the number ofclear sections (track circuits) to the next
train ahead, and the platform that thetrain will arrive at. The received data iscompared with data about track circuit
numbers saved in the train on-board
memory and the distance to the next train
ahead is computed. The on-board
memory also saves data on track gradients,and speed limits over curves and points.
All this data forms the basis for ATC
decisions when controlling the service
brakes and stopping the train.
Figure 6 shows a running pattern generated
by the digital ATC system. The createdpattern determines the braking curve tostop the train before it enters the next
track section ahead occupied by anothertrain. An alarm sounds when the train
approaches the braking pattern and thebrakes are applied when the braking pattern
is exceeded. The brakes are applied
lightly first to ensure better ride comfort,
and then more strongly until the optimum
deceleration is attained. The brakes areapplied more lightly when the train speed
drops to a set speed below the speed
limit. Regulating the braking force in thisway permits the train to decelerate inaccordance with the braking pattern,
while ensuring ride comfort.
There is also an emergency braking

pattern outside the normal braking pattern
and the ATC system applies the emergency
brakes if the train speed exceeds thisemergency braking pattern.
The digital ATC system has a number ofadvantages: (1) Use of one-step brake
control permits high-density operations
because there is no idle running time due
to operation delay between brake releaseat the intermediate speed limit stage. (2)Trains can run at the optimum speed withno need to start early deceleration because
braking patterns can be created for any
type of rolling stock based on data fromwayside equipment indicating the distanceto the next train ahead. This makes mixed
operation of express, local, and freighttrains on the same track possible at the
optimum speed. (3) There is no need tochange the wayside ATC equipment
when running faster trains in the future.
The Railway Technical Research Institute(RTRI) is currently conducting basic
research into an improved and innovativeATC for Tokyo’s Yamanote Line and theshinkansen lines.

CARAT and ATACSUse of track circuits to detect trains inblocks and to send transmissions from theground to the train requires a lot of waysideequipment. A Computer And Radio

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3

2

1

0

Number of clear track sections ahead

On-board ATC speed signal indications

Aided Train control system (CARAT) is
being developed to reduce the equipment
amount and permit on-board detectionof train locations without using track
circuits. CARAT will control train traffic
by transmitting information between the
ground and trains. The system is similar
to the digital ATC system in the sense thatwayside equipment will transmit informationon the distance to the next train ahead,and braking patterns will be created on
board. However, CARAT will be able toobtain accurate information on train
locations, and transmission of informationfrom the trains to the wayside equipment
will make it possible to create moving
blocks. As Figure 7 shows, CARAT will
be a comprehensive train control systemcapable of transmitting commands fromtrains to station points and level crossings.
RTRI has already conducted CARAT
verification experiments on JR’s Joetsu
Shinkansen. JR East has conducted
subsequent performance tests on its SensekiLine, to test the Advanced Train Administration
and Communications System (ATACS),
which uses radio telecommunications.
One purpose of these tests was to verify
that the system is safe for track maintenancepersonnel. Development of these systems
is continuing, with every reason to believethat they will soon come into service.

Japan Railway & Transport Review 21 • September 1999

47

Technology

Figure 7 CARAT System

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on
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St

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in
tra ionnt sitrre t po Xu
C ren t X
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3

6 km

ain

hin

TRAIN
APPROACHING

ap

pro

ac

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g ala
ssin
l croconds
e
v
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t le
Star in 7 s
in
K
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tra Z
rier
nt t ZBar
re n ar
Cu sitiopolev Trainel c
ros aheasin d agb tZ
arr Z,
ierS
dow
cro tart lessin venin 7 g a l
sec larm
ondsTrRadio basestationControl centre

Level crossing

MarkerLand-based control system

Land-based control system

Interlocking device
Land-based control system

Figure 8 CTC System
Central traffic control centre
Signal display
Train ID display
Display board
Train diagram
automaticrecorderControl board
Track section
interlock
Facsimile

Central controller

Centraltrain radiotransmitter
Facsimile
controllerTraindiagramrecordercontroller

CTC
Centralcontroller

Display current (code)
Control current (code)
Facsimile
receiver48

CTC Station equipment CTC Station equipment

CTC Station equipment

CTC Station equipment

Interlocking equipment

Interlocking equipment

Interlocking equipment

Interlocking equipment

Station A

Station B

Station C

Station D

Japan Railway & Transport Review 21 • September 1999

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Train Traffic Control Systems
CTC and PRC Train traffic control
systems
Train traffic control requires full andcontinuous knowledge of the train operations.
In a conventional traffic control system,
stations use telephone communications toestablish a route, but this process is too
slow and inefficient for modern rail traffic
volumes.
Centralized Traffic Control (CTC) provides
the traffic control centre with informationon the situation of all trains in all track
sections and permits the centre tocontrol train routes directly (Fig. 8). The
heart of the centre is a number ofcentralized display and control panels,
connected to stations and trains by various
types of equipment: radio equipment,command telephones, train schedule
recorders, train number display units, etc.
When the CTC system was first introduced,
train routing was controlled directly byCentre personnel. However, the increasing
number of trains overwhelmed thesystem, prompting development of thecomputerized Programmed RouteControl (PRC) system.
CTC was used for the first shinkansen
operations in 1964, but routing decisions
were automated in 1972. The shinkansen
COMputer aided TRAffic Control system(COMTRAC) has a number of advanced
functions, including route control, traffic
coordination, rolling stock management,
and passenger information services.
COMTRAC is an extremely efficient traffic
control system, so it is used for some nonshinkansen services as well. The JRs andprivate railways have installed or are
installing it on most track sections withhigh-density or high-priority operations.

COSMOS (COmputerized Safety
Maintenance and Operation Systems for
Shinkansen) and integrates existing
COMTRAC functions with traffic planning,
traffic administration, maintenanceequipment control, and rolling stock
control. Route control is not undercentralized control. Instead, routing
responsibility is shared with individual
stations so that if the system fails at one
or several stations or at the Control Centre,
the effect on the system as a whole will
be minimized and some traffic will continue
to flow.
The Autonomous decentralized Transport
Operation System (ATOS), a new andvery powerful traffic control system isbeing implemented for the Tokyo region
to control 17 track sections, 390 stations(140 interlocked), and 6200 daily train
operations. The system first enteredservice in 1996 on JR East’s Chuo Line.
ATOS and COSMOS are very similar—
ATOS began first, but efforts were focusedon COSMOS as the shinkansen control
system. ATOS is far bigger than COSMOS,
so the latter was put into service sooner.

Wireless Communications
DevicesNarrow-gauge train radio
communications
Train safety would be far lower without
radio communications between traincrews and control centre staff. Before theintroduction of train radio, a crew
member would have to use a tracksiderailway telephone to call the control centre if
an accident occurred outside a station.
Today, the train crew can communicate
immediately with the control centre using thetrain radio.
Railways use duplex, semi-duplex andsimplex radio telecommunications fornon-shinkansen lines. Duplex is used on
sections with heavy traffic, semi-duplex
is used on high-priority sections with lessdense traffic, and simplex is used on othertrack sections. The simplex system is
actually an extension of the existing systemthat drivers and train crew already used
to communicate with each other. Semiduplex and simplex systems are also used
for communication between train crews.
Japan’s private railways also use train
radio communications. The type depends

COSMOS and ATOS
JR East improved the COMTRAC system
in 1998 when it opened the Hokuriku
Shinkansen. This system is called

COSMOS Shinkansen command centre

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(JR East)

Japan Railway & Transport Review 21 • September 1999

49

Technology

on the specific track sections. Private
trains also have limited-range (1 km)
radio equipment that broadcasts anaccident warning signal directly toapproaching trains in order to prevent a
second accident.

Figure 9 Installation of Leaky Coaxial Cable along Shinkansen Tracks(a) LCX-C480 structure

Cable support

Shinkansen radio communications

Insulator

Shinkansen trains have used radio
communications since the very firstservices in 1964 but Japan's mountainous
topography makes radio communications
very difficult in some locations. Anotherproblem of the early shinkansen days was
the small number of available radio channels.
To ensure better reliability and to increase
the number of communications channels,
leaky coaxial (LCX) cables were laid firstalong the full length of both the Tohoku
Shinkansen and Joetsu Shinkansen totransmit data and messages to and fromcommand and track telephones, andon-board public telephones. LCX cables
were subsequently laid along the Tokaido
Shinkansen as well. Figure 9 shows theinstallation details; the supported LCX
cable is run along the noise-control barrier
beside the track, with suitable-size slots
cut into the cable to allow the signal toleak out.

Inner
conductor

Conclusion
This article has described some signalling
equipment used by Japanese railways toensure safe railway operations. Other
devices, such as interlocked signals andpoints in stations are used as well. Mostof the many thousands of interlocks areeither relay or solid-state electronicinterlocks and there are about 1000 of
the latter now in service.
In addition, almost all level crossings inJapan are controlled by automatic devices
that detect an approaching train andlower the barriers automatically. Somelevel crossings on very busy roads haveextra obstruction warning devices to50

Cross section

Slots

Leaky coaxial cableOuter
conductor

Outer structure
Inner conductor

Outer
conductor
Insulator
Inner structure(b) LCX position along shinkansen tracks

LCX

Antennas

LCX

detect motor vehicles on the crossing
when the barriers come down and stop
the approaching train.
However, although all signalling devices

play an essential role in railway safety,
there is still no substitute for skilled,
conscientious and vigilant operations
staff.
■

Kanji Wako
Mr Kanji Wako is Director in Charge of Research and Development at the Railway Technical Research Institute (RTRI). He
joined JNR in 1961 after graduating in engineering from Tohoku University. He is the supervising editor for this series on
Railway Technology Today.

Japan Railway & Transport Review 21 • September 1999

Tetsuo Takashige
Mr Takashige is Chief Engineer of the Signalling Systems Group at RTRI where he has worked since1974. He joined JNR in 1973 after obtaining a Masters degree in Electrical Engineering from Kyoto
University.

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