1. ‘Communication’  Based Train Control Systems

Train control has advanced from conventional fixed block system to moving block technology during the last three decades. Many highly dense cities realized the need for moving commuters in a large scale, especially during peak hours and frequent train operation under 3min or less is inevitable.. This is often referred as Headway among the Technical diaspora. Headway can be put it in simple words “The theoretical time separation between two Trains travelling in the same direction on the same track. It is calculated from the time the head-end of the leading Train passes a given reference point to the time the head-end of the following Train passes the same reference point”  It is possible to achieve tight 3 min headway with the help of automatic signalling ,however this is possible at the expense of  large amount of signalling asset maintained and less safety .Not forgetting the fact that Automatic train Protection system can be implemented for  safety enforcement but large number of standalone ATP system are getting obsolete  (Example :Hitachi L10000) within next decade .large scale greenhouse gas emission reduction also boosted the requirement for large scale passenger and freight movement with utmost safety and energy efficiency .Thanks to  Paris agreement often referred as Paris Accords adopted in 2015 .Headway requirements are relatively low for Mainline and freight however the need  for enhanced  safety and  efficiency are ever growing .There are pros and cons for the most popular train control systems .

2. Communication Based Train control System (CBTC)

As per Institute of Electrical & Electronics Engineers (IEEE 1474 ) CBTC is a “A continuous automatic train control system utilizing high-resolution train location determination, independent of track circuits; continuous, high capacity, bidirectional train-to-wayside data communications; and trainborne and wayside processors capable of implementing vital functions” They do possess the following characteristics

• Determination of train location, to a high degree of precision, independent of track circuits.
• A geographically continuous train-to-wayside and wayside-to-train data communications network to permit the transfer of significantly more control and status information than is possible with conventional systems.
• Wayside and train-borne vital processors to process the train status and control data and provide continuous automatic train protection (ATP). Automatic train operation (ATO) and automatic train supervision (ATS) functions can also be provided, as required by the particular application

It is not necessary that train shall be in unattended mode (driverless) to be identified as a CBTC. Any system that performs the above-mentioned functionality can be identified as a Communication Based Train Control System. Even though IEEE definition didn’t expect the need for a secondary train detection system, majority of the suburban network make use of a secondary Train detection system such as Track circuits or Axle counter for the degraded mode of operation in case the complete loss of communication. CBTC is mentioned as the train control system used in urban mobility  per IEEE definition rest of  this article ,even though European Train Control System or Positive train Control System also based on wayside to train communication.

3. Utilisation of Moving Block in CBTC

Conventional railway system works on Fixed block system where each blocks are defined and separated with safe distance(braking distance)   with safety margin  and only one train possible in a longer block at a time and the leading  train has to clear the block before following train can occupy the block.Where as in moving block  train as a “moving block “ maintain safe distance based on braking curve with a safety margin .Refer below figure to identify the difference. There is an article  with comparison is posted in RailFactor ,and detailed comparison between traditional fixed block and moving block is out of scope for this article.

Fig 1: Traditional Fixed Block System

Fig 2: Moving Block System

4. European Train Control System (ETCS)  

Evolved from the need for economic integration of the European Union for inter operation of their Trains .There were different signalling principles ,’non standardized ‘ signalling equipment existed in conventional system giving nightmare to operate between boarders with multiple train borne  systems(Turn off and Turn On )  to cross the boarder ,even crew were needed to change during boarder crossing  irrespective of same gauges between boarder. A technical specification for interoperability was embraced by the European parliament and the council of Union on the interoperability of the European rail system in accordance with the legislative procedure. Major Rail System providers from Europe known as Unisig companies under European Union Agency for Railways   jointly produced the rules  described in ‘Subsets”  .So far ETCS has five  levels (Application Level 0, Level NTC ,Level 1 ,Level 2 and Level 3)  as described in SUBSET-026-2 . Global System for Mobile Communications-Railway(GSM-R) is the  mode of data transmission between train and regulation centres (Wayside and Train borne) for ETCS Level 2 . Considering the fear that next 10 years will phase out the GSM-R  and various ETCS Level 2  implementation planned will impact.It could be implemented  with Long Term Evolution (LTE)  digital Radio System.LTE is normally regarded as 4G protocol  and the Future Railway Mobile Communication System (FRMCS) is considering to move something similar to 5G.

Note :- European Rail Transport Management System ( ERTMS) include ETCS +GSM-R

5. Positive Train Control System (PTC)

A communication-based Train monitoring and control system with a train protection system originated for the North America. As defined by AREMA (The American Railway Engineering and Maintenance of Way Association ) a Positive  Train Control System has the primary characteristics of Safe Train Separation to avoid train collision ,Line speed Enforcement ,Temporary Speed Restrictions ,Rail worker safety and Blind spot monitoring .As published in Digital Trends PTC work by ” combining radio, cellular and GPS technology with railway signals to allow trains to identify their locations relative to other trains on the track “Concept wise”  in a way PTC and ETCS are same.

6. East Japan Train Control (EJTC)

Classified as four levels from Level 0 to Level 3 .Level 0 make use of an Automatic Train Stop device (ATS-S)  to prevent collision .This has been replaced with Automatic Train Stop device Pattern Type (ATS-P) in Level 1 addressing the weakness in ATS-S .New development with EJTC Level 3  make use of radio transmission and train itself detect its location and communicate with other trains .EJTC Level 3 is named as Advanced Train Administration and Communication System ( ATACS )  using Autonomous Decentralized System (ADS)  Technology. ADS technology is considered as most innovative modern technology for smart trains by Dr. Kinji Mori from Japan. This decentralized system composed of modules designed to operate independently capable of interacting each other to achieve the over all goal of the system. This innovative design enables the system to continuously function even when the event of components (modules ) failures .This plug and play module also enable  to replace the failed module while the overall system is still operational. Refer Figure 3  for message passing in an autonomous decentralized system.

               Fig 3: Architecture for Autonomous Decentralized System     

ADS  is a decoupled architecture where each subsystem communicates by message passing using shared data fields .Uniqueness of ADS system is that it doesn’t contain a central operating system or coordinator. Instead of that each subsystem manages its own functionality and coordination with other subsystems. When a subsystem needs to interact with other subsystems it broadcasts the shared data fields containing the request to all other subsystems. This broadcast does not include the identification or address of any other subsystem. Rather the other subsystems will, depending on their purpose and function, receive the broadcast message and make their own determination on what need to be done with it or ignore. Data transmission can be carried out by Enterprise Service Bus (ESB) .It operates in the autonomous decentralized system

7. Chinese Train Control System(CTCS)

Largely based on ETCS except CTCS has Six Levels. China has a large rail network constitutes of several types of rail network such as High Speed, conventional, passenger and freights and realized the dire need for standardization, that is the basis for CTCS. Like ETCS ,CTCS also make use of balises on CTCS Level 2 and Level 3 .However Wuhan -Guangzhou high speed line uses ETCS Level 2 .China From year  2016 onwards  all metro lines in China are required to utilise LTE as the basis of their communications network.

8. Definition Standards for CBTC and ETCS

This section depicts the major requirement specification for both the technology .Its recommended to refer these standards .

In further chapters will cover case study and standard references for subsystems for each  elements to build a ETCS and CBTC systems .

1. ETCS (All Levels) -ERA UNISIG EEIG ERTMS USERS GROUP

• SUBSET-026 - System Requirements Specification
• SUBSET -027 - FIS Juridical Recording
• SUBSET -034 - Train Interface FIS
• SUBSET-035 - Specific Transmission Module FFFIS
• SUBSET-036 - FFFIS for Eurobalise
• SUBSET-037 - EuroRadio FIS
• SUBSET-038 - Offline Key Management FIS
• SUBSET-039 - FIS for RBC/RBC handover
• SUBSET-044 - FFFIS for Euroloop
• SUBSET-047 - Trackside-Trainborne FIS for Radio infill
• SUBSET-056 - STM FFFIS Safe time layer
• SUBSET-057 - STM FFFIS Safe link layer
• SUBSET-058 - FFFIS STM Application layer
• SUNSET-098 - RBC-RBC Safe Communication Interface
• SUBSET-100 - Interface "G" Specification
• SUBSET-101 - Interface "K" Specification
• SUBSET 114 - KMC-ETCS Entity Off-line KM FIS
• SUBSET-137 - On-line Key Management FFFIS
• ERA_ERTMS_015560 - ETCS Driver Machine Interface

 

2. CBTC

• IEC 62290-1:2014- Railway applications - Urban guided transport management and command/control systems - Part 1: System principles and fundamental concepts.

• IEC 62290-2:2014-Railway applications - Urban guided transport management and command/control systems - Part 2: Functional requirements specification.

• IEC 62290-3:2019- Railway applications - Urban guided transport management and command/control systems - Part 3: System requirements specification.

• IEEE 1474.1 - Communications-Based Train Control (CBTC) Performance and Functional Requirments
• IEEE 1474.2 - User Interface Requirments in Communications-Based Train Control (CBTC) Systems
• IEEE 1474.3 - Recomended Practice for Communication-Based Train Control (CBTC) System Design and Functional Allocation
• IEEE 1474.4(Draft) - Recomended Practice for Communication-Based Train Control (CBTC) System
• IEEE 1482.1 - Rail Transite Vehicle Event Recorders
• IEEE 802.11 - IEEE Standard for Information Technology — Telecommunications and Information Exchange between Systems Local and Metropolitan Area Networks — Specific Requirements
  
• IEEE 29148 - Systems and software engineering - Life cycle processes - Requirements engineering - IEEE Computer Society
• IEEE 828 (Configuration Management ) - IEEE Standard for Configuration Management in Systems and Software Engineering
• IEEE 12207 (Software Life Cycle Process) - Systems and software engineering — Software life cycle processes
• IEEE 15288(System Life Cycle Process) - Systems and software - Systems life cycle processes
• IEEE 24748 (System &Software Engineering ) - Systems and software engineering — Life cycle management
• IEEE 802.3 (LAN Interface) - IEEE Standard for Ethernet

9. Comparison between CBTC and ETCS

As mentioned before CBTC is based on Institute of Electrical & Electronics Engineers (IEEE) defined requirements where as ETCS is based on Subsets from ERA * UNISIG * EEIG ERTMS USERS GROUP.Refer Below table  for some of comparison between CBTC and ETCS solution.

10. Selection of System (food for thought !)

It is also vital to select the best suitable solution for the rail network, especially brownfield based on your operational needs, track alignment, type of rollingstock operating on the line, whether track is laid on viaduct /at grade or Tunnel. Sometimes it could be tricky.

Let me explain a complex scenario of a suburban network, with varying distance between stations which  could be in between  1km to 25km .It is currently operating with a fixed block system operating 12 Trains Per hour during peak time and 7 Trains per hour on non-peak hours and the  future patronage for the next 50 years are identified as 25- 28 train per hour during peak and 12 Trains during  non-peak hours  . Track is laid on Tunnel for some sections, and majority are either on ground  or viaduct /bridges. Network need to operate long freights on non-peak hours  which cannot be fitted with trainbourne equipments .It also shares main land trains with similar scenario on non peak hours . Network  has active level crossing  through out  the network .Below table detail some of the ideal solution in terms of cost (especially when many long sections are present ,implementing and maintaining  a DCS /Wifi will be expensive ) .What do you select as the ideal  solution in this scenario ?