Railway Technology Today 8 (Edited by Kanji Wako) Signalling Systems for Safe Railway Transport Tetsuo Takashige

T Technology

echnolo Railway Technology Today 8 (Edited by Kanji Wako) Signalling Systems for Safe Railway Transport Tetsuo Takashige

applied—is longer for trains than it is for blocks and to control the signals for each Introduction road vehicles. Consequently, only one block. All double-tracked sections in Japan train can occupy a specific section of track use the automatic block system. As Trains could not run safely without at one time. Such a section of track is Figure 2a shows, there are basically three signalling devices. This article looks at called a block. Track circuits are used to signal aspects: red, meaning stop four tools that ensure railway safety in determine whether a train is in a specific immediately before entering the next Japan: block systems, train control systems, block. track section occupied by an ahead train; train traffic control systems, and wireless Figure 1 shows how the rails form part of yellow, meaning proceed with caution at communications devices. an electric circuit (track circuit). When a speed no greater than 45 km/h (55 km/h the train’s wheels pass a certain point, they or faster is permitted on some sections) as cause a short circuit, preventing electric far as the signal, and green, meaning the Block Systems current from proceeding further. This next track section is clear and the train makes it possible to detect a train in a can enter that section at the maximum Automatic block system block. speed. In heavily used sections, two other Braking distance—the distance needed to An automatic block system uses the track signal aspects are also used (Fig. 2b): two come to a complete halt after brakes are circuit to automatically detect trains in yellow lights (restricted speed), and one yellow and one green light (reduced speed). Figure 1 General Principles of Track Circuit

gy 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 used on single tracks. In many cases, a track circuit system or an electronic block system (electronic coding verification Train system) is used. Both are semi-automatic block systems. Transmitter Receiver Activated relay released The track circuit system controls train by train short-circuiting rails movement in the blocks between stations, and involves interlocking signal levers at

Figure 2 Automatic Block Signalling System

(a) Normal track section STOP CAUTION CLEAR R : Red Y : Yellow G Y R G Y R G Y R G : Green T : Transmitter (power supply)

R : Receiver (track relay) RT RT RT RT

Signal current cut

(b) High-density traffic track section STOP RESTRICTED SPEED CAUTION REDUCED SPEED CLEAR Y Y R Y G Y Y R Y G Y Y R Y G Y Y R Y G Y Y R Y G

RT RT RT RT RT RT

44 Japan Railway & Transport Review 21 • September 1999 Copyright © 1999 EJRCF. All rights reserved. Reproduction in whole or in part without permission is prohibited. Figure 3 Operation of ATS-S System

Alarm Emergency brakes automatically applied rings to stop train if driver fails to brake within 5 seconds 5-second interval

Train 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

Alarm Red light ON, bell rings rings

When driver brakes STOP signal within 5 seconds to stop

White light ON, chime rings White light ON, chime rings

Train stops 5-second interval Emergency STOP signal If driver does not brake brakes applied within 5 seconds to stop

Red light ON, bell rings Red light ON, bell rings

the two stations that a train is travelling with serious loss of life in the early 1960s stops at the ground coil, the train can still between. The train’s departure and arrival resulted in the installation of the so-called proceed under his control through a stop are detected by the track circuits at the Automatic Train Stop (ATS) system signal. So-called 'absolute stop' ground station entrance and exit. throughout Japan. In the ATS system, an coils that do not depend on driver In the electronic block system, each train alarm sounds in the cab when the train ackowledgement are installed in stations has a radio communications device that approaches a stop signal, warning the and at start signals to prevent any possibility transmits the train’s ID. When the driver is driver to stop. If he fails to apply the brakes, of an accident occurring due to the driver ready to leave a station, he presses a the ATS stops the train automatically. moving ahead by mistake. button and the signal changes automatically (Figure 3 shows the operation of the ATS-S A new ATS-P type of system that does not to green. When the train arrives at the system used by the JRs.) depend on driver acknowledgement has next station, the train’s ID is transmitted The ATS system uses ground coils been installed recently, mostly in the to a receiver, clearing the block. This type installed on the track some distance before Tokyo and Osaka regions. Ground coils of electronic block system requires fewer signals. If a train passes a coil when the communicate between the ground and staff because the driver basically controls signal aspect is stop, an alarm is sent the trains (Fig. 4) and train braking patterns the block. immediately to the driver, regardless of are monitored by the ground coils to the train speed. If the driver does not ensure that the trains stop before a stop stop within 5 seconds after the alarm is signal. If a train exceeds the speed Train Control Systems received, the emergency brakes are applied permitted by the braking pattern, the automatically to stop the train. In other service brakes are applied automatically Automatic Train Stop (ATS) words, the emergency brakes are not to stop the train. The train can then The driver must always obey the signal, applied if the driver applies the brakes proceed again, but only in accordance but the possibility of human error can and presses the Acknowledge button. with instructions received from the next cause serious accidents. Two rail accidents However, this means that if the driver coil. This system offers higher safety

levels, because it does not depend on Automatic Train Control (ATC) Automatic Train Operation (ATO) system driver acknowledgement. The Automatic Train Control (ATC) system can automatically control departure from Private railways in Japan have installed was developed for high-speed trains like stations, the speed between stations, and an improved version of the ATS-S system the shinkansen, which travel so fast that the the stop position in stations. It has been throughout most of their networks. This driver has almost no time to acknowledge installed in some subways. system offers on-board speed verification trackside signals. The ATC system sends capability and, since it can apply train AF signals carrying information about the Digital ATC brakes automatically, does not depend on speed limit for the specific track section The ATC system has been used to control driver acknowledgement. along the track circuit (Fig. 5). When all sections of shinkansen tracks ever since In an intermittent control system using these signals are received on board, the the first shinkansen in 1964 and there has coils, no information is received before train’s current speed is compared with the never been a collision. However, ATC has the train passes the coil, meaning that speed limit and the brakes are applied three disadvantages. First, the headway signal changes in heavily used sections automatically if the train is travelling too cannot be reduced due to the idle running do not provide a suitable level of fast. The brakes are released as soon as time between releasing the brakes at one compliance. To alleviate this problem, the train slows below the speed limit. speed limit and applying the brakes at the the railways have installed a continuous This system offers a higher degree of next slower speed limit. Second, the control ATS system for some track sections. safety, preventing collisions that might be brakes are applied when the train achieves This system uses an audio-frequency (AF) caused by driver error, so it has also been maximum speed, meaning reduced ride current to transmit ATS-related information installed in heavily used lines, such as comfort. Third, if the operator wants to along the track circuit, making it possible Tokyo's Yamanote Line and some subway run faster trains on the line, all the related to receive information on board the train lines. relevant wayside and on-board equipment at any time. This system offers similar Although the ATC applies the brakes must be changed first. advantages to the ATC system described automatically when the train speed The digital ATC system uses the track circuits below. exceeds the speed limit, it cannot control to detect the presence of a train in the the motor power or train stop position section and then transmits digital data when pulling into stations. However, the from wayside equipment to the train on

Figure 4 Operation of ATS-P System

Braking pattern created

Transceiver Recorder Brake command Braking pattern Receive Speed logic check Brake Controller unit unit mechanism

On-board transponder Signal aspect and distance TG to stop signal Electrical signal

Ground coils Ground coils Ground coils Passive ground coils at 650 m at 180 m at 30 m (two in unit) No. 3 No. 2 No. 1 Signal aspect data Repeater Repeater Repeater Data circuit (1 pair) Code To central monitoring equipment processor (system supervision) Power supply circuit (1 pair)

TG: Tachometer generator

46 Japan Railway & Transport Review 21 • September 1999 Copyright © 1999 EJRCF. All rights reserved. Reproduction in whole or in part without permission is prohibited. Figure 5 ATC Train Running Pattern Figure 6 Digital ATC Train Running Pattern

Light braking force at first 300 300 Full service braking 275 275 Alarm Running pattern

230 230 Running pattern ATC Signals Braking pattern

170 170 Lighter braking (km/h) (km/h)

120 Train speed 120 Train speed Emergency braking 70 70

30 30

0 0 300 275 230 170 30 4 3 2 1 0 On-board ATC speed signal indications Number of clear track sections ahead the track circuit numbers, the number of pattern outside the normal braking pattern Aided Train control system (CARAT) is clear sections (track circuits) to the next and the ATC system applies the emergency being developed to reduce the equipment train ahead, and the platform that the brakes if the train speed exceeds this amount and permit on-board detection train will arrive at. The received data is emergency braking pattern. of train locations without using track compared with data about track circuit The digital ATC system has a number of circuits. CARAT will control train traffic numbers saved in the train on-board advantages: (1) Use of one-step brake by transmitting information between the memory and the distance to the next train control permits high-density operations ground and trains. The system is similar ahead is computed. The on-board because there is no idle running time due to the digital ATC system in the sense that memory also saves data on track gradients, to operation delay between brake release wayside equipment will transmit information and speed limits over curves and points. at the intermediate speed limit stage. (2) on the distance to the next train ahead, All this data forms the basis for ATC Trains can run at the optimum speed with and braking patterns will be created on decisions when controlling the service no need to start early deceleration because board. However, CARAT will be able to brakes and stopping the train. braking patterns can be created for any obtain accurate information on train Figure 6 shows a running pattern generated type of rolling stock based on data from locations, and transmission of information by the digital ATC system. The created wayside equipment indicating the distance from the trains to the wayside equipment pattern determines the braking curve to to the next train ahead. This makes mixed will make it possible to create moving stop the train before it enters the next operation of express, local, and freight blocks. As Figure 7 shows, CARAT will track section ahead occupied by another trains on the same track possible at the be a comprehensive train control system train. An alarm sounds when the train optimum speed. (3) There is no need to capable of transmitting commands from approaches the braking pattern and the change the wayside ATC equipment trains to station points and level crossings. brakes are applied when the braking pattern when running faster trains in the future. RTRI has already conducted CARAT is exceeded. The brakes are applied The Railway Technical Research Institute verification experiments on JR’s Joetsu lightly first to ensure better ride comfort, (RTRI) is currently conducting basic Shinkansen. JR East has conducted and then more strongly until the optimum research into an improved and innovative subsequent performance tests on its Senseki deceleration is attained. The brakes are ATC for Tokyo’s Yamanote Line and the Line, to test the Advanced Train Administration applied more lightly when the train speed shinkansen lines. and Communications System (ATACS), drops to a set speed below the speed which uses radio telecommunications. limit. Regulating the braking force in this CARAT and ATACS One purpose of these tests was to verify way permits the train to decelerate in Use of track circuits to detect trains in that the system is safe for track maintenance accordance with the braking pattern, blocks and to send transmissions from the personnel. Development of these systems while ensuring ride comfort. ground to the train requires a lot of wayside is continuing, with every reason to believe There is also an emergency braking equipment. A Computer And Radio that they will soon come into service.

Figure 7 CARAT System

3 6 km Train ahead at ZZ, Train approaching level crossing barrier down Control centre Start levelin 7 crossing seconds alarm TRAIN Start level Station entry clear APPROACHING crossing alarm in 7 seconds Barrier OK Current train at XX Radio base Current train current position station position at ZZ

Marker Level crossing Interlocking device Land-based control system Land-based control system Land-based control system

Figure 8 CTC System

Central traffic control centre

Signal display Train ID display

Display board

Train diagram Control board automatic recorder Track section interlock

Facsimile Central controller Central train radio transmitter Facsimile CTC Train controller Central diagram controller recorder controller

Display current (code) Control current (code) Facsimile receiver

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

48 Japan Railway & Transport Review 21 • September 1999 Copyright © 1999 EJRCF. All rights reserved. Reproduction in whole or in part without permission is prohibited. COSMOS (COmputerized Safety Wireless Communications Train Traffic Control Systems Maintenance and Operation Systems for Devices Shinkansen) and integrates existing CTC and PRC Train traffic control COMTRAC functions with traffic planning, Narrow-gauge train radio systems traffic administration, maintenance communications Train traffic control requires full and equipment control, and rolling stock Train safety would be far lower without continuous knowledge of the train operations. control. Route control is not under radio communications between train In a conventional traffic control system, centralized control. Instead, routing crews and control centre staff. Before the stations use telephone communications to responsibility is shared with individual introduction of train radio, a crew establish a route, but this process is too stations so that if the system fails at one member would have to use a trackside slow and inefficient for modern rail traffic or several stations or at the Control Centre, railway telephone to call the control centre if volumes. the effect on the system as a whole will an accident occurred outside a station. Centralized Traffic Control (CTC) provides be minimized and some traffic will continue Today, the train crew can communicate the traffic control centre with information to flow. immediately with the control centre using the on the situation of all trains in all track The Autonomous decentralized Transport train radio. sections and permits the centre to Operation System (ATOS), a new and Railways use duplex, semi-duplex and control train routes directly (Fig. 8). The very powerful traffic control system is simplex radio telecommunications for heart of the centre is a number of being implemented for the Tokyo region non-shinkansen lines. Duplex is used on centralized display and control panels, to control 17 track sections, 390 stations sections with heavy traffic, semi-duplex connected to stations and trains by various (140 interlocked), and 6200 daily train is used on high-priority sections with less types of equipment: radio equipment, operations. The system first entered dense traffic, and simplex is used on other command telephones, train schedule service in 1996 on JR East’s Chuo Line. track sections. The simplex system is recorders, train number display units, etc. ATOS and COSMOS are very similar— actually an extension of the existing system When the CTC system was first introduced, ATOS began first, but efforts were focused that drivers and train crew already used train routing was controlled directly by on COSMOS as the shinkansen control to communicate with each other. Semi- Centre personnel. However, the increasing system. ATOS is far bigger than COSMOS, duplex and simplex systems are also used number of trains overwhelmed the so the latter was put into service sooner. for communication between train crews. system, prompting development of the Japan’s private railways also use train computerized Programmed Route radio communications. The type depends Control (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 non- shinkansen services as well. The JRs and private railways have installed or are installing it on most track sections with high-density or high-priority operations.

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 (JR East)

on the specific track sections. Private trains also have limited-range (1 km) Figure 9 Installation of Leaky Coaxial Cable along Shinkansen Tracks radio equipment that broadcasts an accident warning signal directly to (a) LCX-C480 structure approaching trains in order to prevent a second accident. Cable support Slots Shinkansen radio communications Insulator Inner Shinkansen trains have used radio conductor communications since the very first Outer Leaky coaxial cable conductor services in 1964 but Japan's mountainous Cross section Outer structure topography makes radio communications Inner conductor very difficult in some locations. Another Outer problem of the early shinkansen days was conductor the small number of available radio channels. Insulator To ensure better reliability and to increase Inner structure

the number of communications channels, (b) LCX position along shinkansen tracks leaky coaxial (LCX) cables were laid first along the full length of both the Tohoku Shinkansen and Joetsu Shinkansen to transmit data and messages to and from command and track telephones, and LCX on-board public telephones. LCX cables Antennas were subsequently laid along the Tokaido Shinkansen as well. Figure 9 shows the LCX installation 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 to leak out. detect motor vehicles on the crossing play an essential role in railway safety, when the barriers come down and stop there is still no substitute for skilled, Conclusion the approaching train. conscientious and vigilant operations However, although all signalling devices staff. ■ This article has described some signalling equipment used by Japanese railways to ensure safe railway operations. Other Kanji Wako devices, such as interlocked signals and Mr Kanji Wako is Director in Charge of Research and Development at the Railway Technical Research Institute (RTRI). He points in stations are used as well. Most joined JNR in 1961 after graduating in engineering from Tohoku University. He is the supervising editor for this series on of the many thousands of interlocks are Railway Technology Today. either relay or solid-state electronic interlocks and there are about 1000 of the latter now in service. Tetsuo Takashige

In addition, almost all level crossings in Mr Takashige is Chief Engineer of the Signalling Systems Group at RTRI where he has worked since Japan are controlled by automatic devices 1974. He joined JNR in 1973 after obtaining a Masters degree in Electrical Engineering from Kyoto that detect an approaching train and University. lower the barriers automatically. Some level crossings on very busy roads have extra obstruction warning devices to