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TCRP Web-Only Document 71: A Transit Agency Guide to Evaluating Secondary Train Detection/Protection Systems in Communications-Based Train Control Systems CH2M New York, NY  Contractor’s Final Report for TCRP Project D-18 Submitted April 2017 ACKNOWLEDGMENT This work was sponsored by the Federal Transit Administration (FTA) in cooperation with the Transit Development Corporation (TDC). It was conducted through the Transit Cooperative Research Program (TCRP), which is administered by the Transportation Research Board (TRB) of the National Academies of Sciences, Engineering, and Medicine. COPYRIGHT INFORMATION Authors herein are responsible for the authenticity of their materials and for obtaining written permissions from publishers or persons who own the copyright to any previously published or copyrighted material used herein. Cooperative Research Programs (CRP) grants permission to reproduce material in this publication for classroom and not-for-profit purposes. Permission is given with the understanding that none of the material will be used to imply TRB, AASHTO, FAA, FHWA, FMCSA, FRA, FTA, Office of the Assistant Secretary for Research and Technology, PHMSA, or TDC endorsement of a particular product, method, or practice. It is expected that those reproducing the material in this document for educational and not-for-profit uses will give appropriate acknowledgment of the source of any reprinted or reproduced material. For other uses of the material, request permission from CRP. DISCLAIMER The opinions and conclusions expressed or implied in this report are those of the researchers who performed the research. They are not necessarily those of the Transportation Research Board; the National Academies of Sciences, Engineering, and Medicine; or the program sponsors. The information contained in this document was taken directly from the submission of the author(s). This material has not been edited by TRB.

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IV  Contents  Section ........................................................................................................................................ Page  Summary ............................................................................................................................................. ix  1  Introduction ............................................................................................................................ 1  2  Problem Statement ................................................................................................................. 2  3  List of Acronyms ...................................................................................................................... 3  4  CBTC Technology ..................................................................................................................... 4  4.1  CBTC Equipment ................................................................................................................. 4  4.2  CBTC Train Control Modes .................................................................................................. 5  4.3  Trends in CBTC Projects Around the World ........................................................................ 6  5  Secondary Train Detection/Protection Systems  ...................................................................... 8  5.1  Detection Systems .............................................................................................................. 9  5.2  Protection Functions ......................................................................................................... 11  5.3  STD/PS Implementations .................................................................................................. 12  6  STD/PS Considerations .......................................................................................................... 17  6.1  Consequences of Having an STD/PS ................................................................................. 17  6.2  Consequences of Having No or Minimal STD/PS .............................................................. 21  7  Equipment Failures ................................................................................................................ 22  7.1  CBTC Equipment Failures .................................................................................................. 22  7.2  STD/PS Equipment Failures ............................................................................................... 28  8  Work Trains ........................................................................................................................... 30  8.1  Not Equipping Work Trains ............................................................................................... 30  8.2  Equipping Work Trains ...................................................................................................... 31  8.3  Using a CBTC Equipped Trailer .......................................................................................... 32  8.4  Using a Separate Tracking System .................................................................................... 32  8.5  Minimum Non‐Equipped Train Length Issue .................................................................... 32  8.6  CBTC Work Zone Function ................................................................................................ 33  9  CBTC Category Selection Process ........................................................................................... 34  9.1  Summary of Previous Sections.......................................................................................... 34  9.2  Selection Criteria ............................................................................................................... 35  9.3  Decision Flow Diagrams .................................................................................................... 42  9.4  Other Considerations ........................................................................................................ 50  10  Choosing the Secondary Method of Detection ....................................................................... 52  10.1  Secondary Detection System Layout ................................................................................ 52  10.2  Comparison Between Track Circuits and Axle Counters ................................................... 53  10.3  Industry Survey ................................................................................................................. 55  11  Conclusion ............................................................................................................................. 57  12  Case Studies .......................................................................................................................... 59  12.1  Port Authority of New York & New Jersey, AirTrain JFK Case Study ................................ 59  12.2  British Columbia Rapid Transit Company Case Study, SkyTrain ....................................... 62 

V  12.3  New York City Transit Case Study, Canarsie and Flushing Lines ....................................... 68  12.4  Port Authority Trans‐Hudson Case Study, Positive Train Control ..................................... 73  12.5  Transport for London Case Study, CBTC ........................................................................... 76  12.6  Baltimore Metro Subway Case Study ............................................................................... 79  Tables  1  CBTC Project Categories ............................................................................................................ x  2  Selection Factors of an STD/PS .................................................................................................. xi  3  STD/PS Functional Categories ................................................................................................. 13  4  Examples of STD/PS Drawbacks .............................................................................................. 19  5  Level of Consequences of STD/PS ........................................................................................... 20  6  Not Equipping Work Trains ..................................................................................................... 30  7  Summary of Functions by Category ........................................................................................ 34  8  Meeting the Need for a Mixed‐Fleet Operation ..................................................................... 36  9  Meeting the Need to Operate a Peak Headway with the Secondary System ......................... 38  10  Meeting the Need for Back‐up for Revenue Service ............................................................... 39  11  Meeting the Need to Manage a Single Train with CBTC Failure with the Secondary System  40  12  Work Train Management by Category .................................................................................... 41  13  Category 1.B Secondary Systems Designed to Handle a Single Non‐CBTC Train .................... 47  14  Track Circuits vs. Axle Counters............................................................................................... 53  15  Type of Secondary Detection Equipment in Different Categories of CBTC Projects ............... 56  Figures  1  Category 1.A.1 ......................................................................................................................... 14  2  Category 1.A.2 ......................................................................................................................... 14  3  Category 1.B.1 ......................................................................................................................... 14  4  Category 1.B.2.1 ...................................................................................................................... 15  5  Category 1.B.2.2 ...................................................................................................................... 15  6  Category 1.B.3 ......................................................................................................................... 15  7  Category 2 ............................................................................................................................... 16  8  Example of 1 out of 2 redundancy architecture ...................................................................... 22  9  Example of 2 out of 2 redundancy architecture ...................................................................... 22  10  Example of 2 out of 3 redundancy architecture ...................................................................... 23  11  Decision Flow Diagram for STD/PS Selection .......................................................................... 44  12  Alternate Decision Flow Diagram for STD/PS Selection .......................................................... 46  13  Decision Flow Diagram for STD/PS Selection – Choosing between 1.B Categories ................ 49 

VI  Foreword  TCRP  Web‐Only  Document  71:  A  Transit  Agency  Guide  to  Evaluating  Secondary  Train  Detection/  Protection Systems  (STD/PS)  in Communications‐Based Train Control  (CBTC) Systems discusses STD/PS  technologies and types of CBTC, and provides guidelines for evaluating the implementation of STD/PS on  a CBTC rail network.  The deployment of a new signaling system requires a closely coordinated partnership among rail transit  agencies, CBTC and STD/PS suppliers,  installers, oversight agencies, and other stakeholders. This guide  will be helpful  to  rail  transit agencies,  signaling  system  suppliers, consultants,  safety  regulators, grant  writers,  policy  boards,  and  other  stakeholders  in  evaluating  the  need  for,  and  selection  of,  an  appropriate STD/PS technology for CBTC deployment projects.   This guide has been developed as a result of the research effort conducted by the CH2M team through  review of industry literature and a study of previously completed and ongoing CBTC projects to identify  scope  and  factors  relative  to  the  selection  of  deployment  strategies  and  technology  choices.  The  research effort was based on  the collection of data pertaining  to deployment experience, operational  practices,  and  technical  aspects of  a CBTC  system with  and without  STD/PS. The principal means  for  collecting this data were visits and  interviews with rail transit agencies and CBTC suppliers  involved  in  major CBTC projects.  The  research  approach  involved  a  two‐phase  process.  The  first  phase  focused  on  data  collection  and  compilation utilizing  literature review and  industry surveys of rail transit operators and CBTC suppliers  to understand the decision‐making processes behind STD/PS implementation. The second phase of the  research  focused  on  the  selection  of  rail  transit  agencies  for  case  studies,  which  involved  direct  site  visits,  in‐person  interviews,  observation  and  data  collection  on  typical  CBTC  operating  practices  and  reliance  on  STD/PS.  This  guide  has  been  developed  with  the  help  of  six  CBTC  implementation  case  studies. 

VII  Author Acknowledgments  The  Transit  Agency  Guide  to  Evaluating  Secondary  Train  Detection/Protection  Systems  (STD/PS)  in  Communications‐Based Train Control  (CBTC) Systems was  conducted  through  the Transit Cooperative  Research  Program  (TCRP), which  is  administered  by  the  Transportation  Research  Board  (TRB)  of  the  National Academy of Sciences. This guide was developed under TCRP Project D‐18 by  the CH2M New  York City‐based  rail  transit  team  (prime contractor), and  supported by  Integrated Strategic Resources  (ISR) Consultants.  The CH2M team was led by Kenneth Diemunsch, CSEP (Principal Investigator). The co‐investigators were  Stuart Landau, PE, MIRSE, Signal and Train Control Engineer; Girish Ananthashankaran, Senior System  Engineer;  Tedd  L.  Snyder,  PE,  Senior  System  Engineer;  Stuart  Hymowitz,  Signal  Engineer;  Muamer  Dedović,  Rolling  Stock  System  Integration  Engineer;  and  Robert  F.  Spero,  Rail  Operations  Specialist.  Special thanks go to Elizabeth Royzman and Christine Martino for their project support in compiling the  information  received  from  different  agencies  and  overall  assembly  of  the  guide,  and  Girish  Ananthashankaran for providing guidance during the project.   The project  team  thanks  the  transit agencies and CBTC suppliers who  took  the  time  to meet with  the  project team, accommodate requests for information, arrange for tours of their facilities, participate in  the  survey  and  case  studies,  and provide  feedback on CBTC  systems  and projects  around  the world.  Their assistance and input were invaluable in helping to shape this guide. In particular, the team thanks  the  agencies  which  participated  in  the  case  studies:  New  York  City  Transit  (New  York,  NY,  USA);  Transport for London (London, UK); AirTrain JFK (New York, NY, USA); Maryland Transit Administration –  Baltimore Metro  Subway  (Baltimore, MD, USA); British Columbia Rapid Transit Company  (Vancouver,  BC, Canada); and Port Authority Trans‐Hudson (Jersey City, NJ, USA).  The  project  team  thanks  the  following  signaling  suppliers  for  their  valuable  contributions:  Ansaldo  Signaling  and  Transportation  Systems  (Pittsburgh,  PA,  USA);  Alstom  Transport  (Saint‐Ouen,  France);  Bombardier Transportation (Pittsburgh, PA, USA); China Railway Signal & Communication Co. (Shanghai,  China);  Siemens  Mobility  ‒  Rail  Automation  (Châtillon,  France);  Thales  Transportation  Solutions  (Toronto, ON, Canada); and Frauscher Sensortechnik GmbH (Marienkirchen, Austria).   The project team thanks the TCRP D‐18 Board for their support and overall feedback on the project. 

VIII  Abstract  The top priorities of any signaling system have always been ensuring safe movement and separation of  trains,  prevention  of  injury  to  personnel  and  patrons,  and  optimization  of  system  capacity.  These  objectives can be achieved by using various service‐proven and mature technologies. The advantages of  Communications‐Based Train Control (CBTC) technology are substantial. In addition to capacity increase,  the  system  offers  the  potential  to  optimize  maintenance  effort,  operational  flexibility,  and  system  management capabilities, thereby maximizing the overall return on capital investment. Despite the fact  that operating and performance benefits of CBTC  technology have been well demonstrated on many  systems  around  the world over  the past decades,  some  agencies  still prefer  to  supplement  it with  a  secondary  train  detection/Protection  System  (STD/PS).  This  STD/PS  may  consist  of  a  conventional  interlocking implementation with track circuits or axle counters.  The  purpose  of  this  guide  is  to  provide  a  practical  approach  to  evaluating  the  appropriate  level  of  STD/PS  for a given CBTC  application.  In  terms of detection,  track  circuits and axle  counters are both  considered  and  compared,  including  the  broken  rail  detection  capabilities  of  track  circuits  and  the  possibility of having no secondary detection at all.   The  first  part  of  this  guide  presents  different  STD/PS  technologies,  and  discusses  CBTC  deployment  trends  and  feedback  on  operations  from  rail  transit  agencies  around  the  world.  The  second  part  provides guidance  for selection of an appropriate  level of STD/PS,  in  terms of candidate  technologies,  product maturity, and potential risks. This evaluation  is  intended to be used during the early stages of  CBTC procurement projects. Case studies are provided at the end of the guide. 

 IX    Summary  Communications‐Based Train Control (CBTC) is one of the most advanced train control systems available  to transit agencies; it enables transit agencies to make maximum use of the infrastructure configuration  by allowing the trains to run closer to each other in comparison to other signaling systems. Deployment  of CBTC technology in the United States has been limited so far due in part to a perception of higher cost  and apparent difficulty with implementation and operation of this technology in comparison with other  signaling systems. This perception of high cost is primarily driven by the expectation that CBTC systems  require an additional,  independent signaling system  to detect and protect  trains  in  the event of CBTC  system failure. This is particularly true for re‐signaling projects in a brownfield environment (that is, an  upgrade of  an  existing  system;  compared  to  greenfield  projects which  are new  clean‐sheet  systems)  where the implementation of CBTC must consider existing operational, maintenance, and infrastructure  constraints. Research was conducted  to evaluate  the need  for an additional  signaling  system and  the  different types of signaling systems that could be used to manage CBTC failures. The research resulted in  the  present  guide;  its  goals  are  to  help  transit  agencies  decide  if  an  additional  signaling  system  is  needed, and if so, the appropriate type of secondary system.  The  Institute of Electrical and Electronics Engineers  (IEEE), Std 1474.1, Standard  for Communications‐ Based  Train  Control,  Performance  and  Functional  Requirements,  defines  CBTC  as  a  continuous  automatic train control (ATC) system utilizing:  • High‐resolution train location determination, independent of track circuits  • Continuous, high capacity, bidirectional train‐to‐wayside data communications  • Train‐borne and wayside processors capable of implementing vital functions  The four primary components of a CBTC system are:  • Train‐borne equipment  • Wayside equipment  • Data communications equipment  • Automatic Train Supervision (ATS) equipment  CBTC has been used for more than 30 years all around the world in mass transit projects, initially on new  lines and progressively on signaling upgrade projects where the transit agencies needed to address one  or more requirements including:  • Improved capacity  • Replacement of a system at end of life  • Enhanced train protection with continuous speed enforcement  • Enhanced roadway worker safety  CBTC has been used for all modes of train operation, from manual to driverless. It has been deployed on  a wide range of transit modes, from airport people movers, to light rail systems, to metros/subways, and  to commuter rail lines.  In addition to CBTC, an additional signaling system is usually considered and implemented that provides  back‐up  in  the  case of CBTC  failures  (both wayside and  carborne) and  to  support unequipped  trains,  such as work trains. The additional signaling systems in this guide will be referred to as secondary train  detection/protection  systems  (STD/PS) or  simply  secondary  systems, which provide  train detection as  well as  train protection  functions. Another name commonly used  is “fallback  system,” given  that  it  is  used  in  the  event  of  CBTC  system  failures.  They  are  called  secondary  systems  or  auxiliary  wayside  systems because CBTC is the primary train control system. All worldwide CBTC suppliers have experience 

X  experience  with  secondary  signaling  systems  and  can  offer  integrated  solutions  as  part  of  their  respective CBTC packages.   Either track circuits or axle counters can be used for train detection. Several types of track circuits have  been used by the rail  industry for more than a century, using the rails as part of a circuit to detect the  presence of trains. Train wheels and axles shorting the rails together de‐energize a track relay or other  detection  device  to  indicate  occupancy.  If  a  wire  or  rail  breaks,  the  effect  is  the  same  as  a  train  occupying  the  track  circuit;  this  is  an  operational  nuisance  but  more  importantly,  is  safe  since  approaching trains will be stopped. The operation is simple, continuous, and fail‐safe.   Axle counters are a proven technology and have been used for decades, although they have very limited  implementations in the United States. This technology uses wheel sensors attached to the running rails  that detect passing  train wheels  (axles). Evaluator equipment  then  computes  the difference between  the number of wheels entering an area and the number exiting the area to determine train presence.  Some of the reasons why the use of axle counters has been  limited  in the United Sates  is because the  transit agencies are familiar with track circuits, have developed trust in their performance for achieving  train  detection,  and  because,  unlike  track  circuits,  axle  counters  are  not  able  to  detect  broken  rail.  However, despite these reasons, more and more CBTC projects are using axle counters as a secondary  method of detection.   The industry survey resulted in the following CBTC project categories:  Table 1: CBTC Project Categories  Category  Type  1.A Secondary System capable of revenue service   1.A.1  Secondary System capable of peak revenue service  1.A.2  Secondary System capable of off‐peak revenue service  1.B Secondary System designed to handle a single non‐CBTC train   1.B.1 Capable of one train per interstation  1.B.2 Capable of one train in between two interlockings  1.B.2.1 With detection devices everywhere  1.B.2.2 With detection devices only at interlocking  1.B.3 Without territory specific headway performance  2  No Secondary System  Two key consequences of having an STD/PS are the effort to deploy the new signaling system and the  additional maintenance needed to maintain both the secondary system and the CBTC system. These key  consequences  impact  the  cost  of  deployment  and  the  operation  of  the  system.  Another  major  consequence of having a secondary system is that the availability of the overall signaling system is lower  than  with  CBTC  only.  This  can  be  due  to  having  more  equipment  to  support  both  systems  and  a  corresponding  increase  in overall system complexity.  It  is  important  to keep  these drawbacks  in mind  when considering the benefits of having an additional signaling system.  Alternatively, not having an STD/PS has two drawbacks: reliance on procedures in case of CBTC failures,  which is vulnerable to human error, and the potential need to equip some of the work trains with CBTC  technology to allow for mixed operation with both CBTC and non‐CBTC trains without impact to revenue  service.  

XI  The result of the industry survey showed that work trains are handled differently by each transit agency  without any direct  relationship  to  the presence or  type of  secondary  system. The method  to manage  work trains does not necessarily need to influence the selection of a secondary signaling system. There  are different prevalent methods of managing work train operation:  • Use operating procedures to manage work train movement. This could be a challenge to manage for transit agencies that operate 24/7. • Equip work  trains with CBTC  equipment,  capable of  full CBTC protection or  capable of  reporting position only, with the protection being managed by operating procedure. Equipping work trains can be  implemented by fitting onboard equipment on the train or by attaching a trailer or  locomotive equipped with CBTC. The different factors to consider when selecting the possible secondary system appropriate for a specific  transit agency are summarized below:  Table 2: Selection Factors of an STD/PS  #  STD/PS Purpose  Comments  1  Mixed‐fleet  operation  The  need  for  mixed‐fleet  operation  with  CBTC  and  non‐CBTC  trains  is  mainly  related  to  the  cut‐over  strategy with  regards  to  the  integration of  the onboard  CBTC equipment on  the  trains. Where not all  trains are equipped with CBTC at  the  beginning  of  CBTC  operations,  a  secondary  system  capable  of  peak  performance is needed (Category 1.A.1), at least temporarily, until all CBTC trains  are equipped and the system can be changed to another category.  2  Run peak headway  Based on the industry survey, the only possible reason to deploy and maintain an  STD/PS capable of peak headway performance is if trains which are not equipped  with CBTC are operating often on  the  line. This may be  the case on part of  the  lines where  trains  from non‐CBTC  lines need  to  transfer  from  the yard  to  their  own operating line. The need to run a peak headway results in Category 1.A.1.   A system capable of peak operation may also be useful during the cut‐over period  from  the  legacy  system  to  the new CBTC  system.  In  some  cases, projects have  started being compatible with peak headway (Category 1.A.1) and then modified  to only provide off‐peak revenue service in a second step (Category 1.A.2).   3  Back‐up for  revenue  service  Though  the availability of a CBTC system  is usually specified as more  than 99%,  the issue of having a fallback system is often raised for CBTC projects deployed on  a particularly busy  line. Characteristics of the  lines such as alternative modes of  transportation,  crowd  control,  or  distance  between  stations  should  be  considered. This option corresponds to a 1.A.2.  4  Management  of a single  train with  CBTC failure  This matter  is closely related to the need for a back‐up system for the complete  line and similar considerations should be  taken  into account. Results may show  that there is no need to have a full back‐up system able to handle wayside CBTC  failure, but there  is a need to manage a single train with CBTC failure efficiently  and  automatically  by  a  signaling  system  instead  of  completely  by  operating  procedures. In this case, project Category 1.B is selected. Depending on the ratio  between operating procedures and automatic management of a single train with  CBTC failure, projects have decided to opt for Category 1.B.1, 1.B.2, or 1.B.3. 

XII  #  STD/PS Purpose  Comments  5  Management  of Work  Trains  Managing  work  trains  is  not  necessarily  part  of  the  decision  process.  When  managing work  trains,  the selection process must consider  if  the  transit agency  has  24/7  operation,  where  work  trains  would  operate  around  and  with  CBTC  revenue  service  trains.  In  this  case,  either  the  decision  is made  to  equip work  trains  with  CBTC  or  there  must  be  a  secondary  system  to  facilitate  their  operation, and projects  in Category 1.B would be  sufficient. For projects with a  secondary system, similar to the management of a single train with CBTC failure,  depending on the headway performance required for work trains, agencies could  opt for Category 1.B.1, 1.B.2, or 1.B.3.  6  Broken Rail Protection  Broken rail protection is an important issue considered in CBTC projects and may  result  in  the perception of needing  track  circuits. Results of  the  research  show  that broken rail protection should not influence the decision to have a secondary  system.  There  are  two  prevalent  methods  to  provide  broken  rail  protection:  detect broken  rails using  track  circuit  failure  indications or detect  rail  flaws by  inspection  and  correct  the  issue  before  the  break  happens.  Inspection  is  done  both visually and with ultrasonic equipment.   When  comparing  track  circuits and axle  counters,  it appears  that  for CBTC  secondary detection, axle  counters have a slight advantage. Axle counters may be installed in parallel to existing track circuits, thus  facilitating the cut‐over on a signaling upgrade program. Also, axle counters have no constraint on the  length of the block which they monitor,  in comparison to track circuits which have a maximum  length.  This  factor suits a CBTC secondary system where block  lengths  in a secondary system are  likely  to be  longer than in a conventional signaling system.  Regulatory and technical aspects must also be considered with the engineering team prior to selection  of  an  STD/PS.  From  a  regulation  point  of  view,  this  research  only  identified  Federal  Railroad  Administration  (FRA)  rules  that mandate  track  circuits, and only one  rapid  transit agency  falls  in  this  category.  A  transit  agency  should  check  with  their  regulatory  authorities  to  confirm  whether  track  circuits are mandated. From a  technical point of view,  the conditions of  the  tracks and rail  inspection  program must be discussed with  the  team  in charge of maintenance of  the  tracks. Evidence  suggests  that agencies could be using more rigorous rail inspection methods to thwart the catastrophic rail break,  regardless of the STD/PS solution. Even with track circuits, only certain rail flaws, such as clean breaks,  are detectable without inspection.  The guide  includes various case studies conducted during the research. All categories of CBTC projects  are  considered with  feedback  on  the  experience  in  deployment  and  operations.  All  transit  agencies  studied had different approaches and  the CBTC projects considered  range widely  in  time periods and  maturity level of the technology, from when CBTC originally emerged, to projects which have not been  awarded. Therefore,  the solution  for each project  is very different and covers a range of perspectives  and  lessons  learned. The goal of the case studies  is to make  the research comprehensive and provide  example templates for transit agencies trying to make selection decisions in similar situations. 

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TRB's Transit Cooperative Research Program (TCRP) Web-Only Document 71: A Transit Agency Guide to Evaluating Secondary Train Detection/Protection Systems in Communications-Based Train Control Systems provides a practical approach to evaluating the appropriate level of secondary train detection/protection systems (STD/PS) for a given communications-based train control system application. In terms of detection, track circuits and axle counters are both considered and compared, including the broken rail detection capabilities of track circuits and the possibility of having no secondary detection at all.

The first part of this guide presents different technologies, and discusses communications-based train control deployment trends and feedback on operations from rail transit agencies around the world. The second part provides guidance for selection of an appropriate level of STD/PS, in terms of candidate technologies, product maturity, and potential risks. The document is accompanied by a PowerPoint presentation.

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