Licentiate Thesis in Transport Science

Challenges for ERTMS related to implementation, technology and railway capacityVAHID RANJBAR

Stockholm, Sweden 2021

kth royal institute of technology

Challenges for ERTMS related to implementation, technology and railway capacityVAHID RANJBAR

Licentiate Thesis in Transport ScienceKTH Royal Institute of TechnologyStockholm, Sweden 2021

Academic Dissertation which, with due permission of the KTH Royal Institute of Technology, is submitted for public defence for the Degree of Licentiate of Engineering on Thursday 27 January 2022 14:15–16:00. Link to the webinar: https://kth-se.zoom.us/j/68075864233

© Vahid Ranjbar© Vahid Ranjbar, Nils O.E. Olsson (2020), Paper 1© Vahid Ranjbar, Nils O.E. Olsson (2020), Paper 2© Vahid Ranjbar, Nils O. E. Olsson, Hans Sipilä (2021), Paper 3 ISBN 978-91-8040-032-9TRITA-ABE-DLT-2144 Printed by: Universitetsservice US-AB, Sweden 2021

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Papers and Declaration of Authorship

This licentiate thesis is based on following papers

I. Vahid Ranjbar, Nils O.E. Olsson (2020) Key challenges of European Rail traffic

Management System, (2020), Proceedings of 8th Transport Research Arena TRA 2020, April

27-30, 2020, Helsinki, Finland.

II. Vahid Ranjbar, Nils O.E. Olsson (2020). Towards mobile and intelligent railway transport:

A review of recent ERTMS related research. In Computers in Railways XVII (Vol. 1, pp. 65–

73). WIT Press.

III. Vahid Ranjbar, Nils O. E. Olsson, Hans Sipilä (submitted to Journal of Rail Transport

Planning & Management, May 2021) Impact of signalling system on capacity – Comparing

legacy ATC, ETCS Level 2 and ETCS Hybrid Level 3 systems.

In these three papers the process of data collection, analysis, synthesizing and more than 90% percent of writing is carried out by the first author (Vahid Ranjbar).

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Abstract

The main purpose of European Rail Traffic Management System (ERTMS) is to remove cross

border barriers and create an interoperable railway network across European countries (Smith

et al. 2012). Since its birth, ERTMS has faced several issues regarding interoperability and

implementation. In addition, one of the main questions for decision-makers and infrastructure

managers regarding ERTMS is determining what level of operation is suitable to implement

and deliver additional performance compared to legacy systems.

This thesis aims to identify challenges for the ERTMS related to implementation, and

interoperability to achieve a mobile and intelligent railway transport system. A subsequent

study on railway capacity is performed. It investigates the impact of ERTMS Hybrid Level 3

(HL3) compared to the European Train Control System Level 2, (ETCS L2) and a Swedish

legacy system, ATC2. To achieve the goals of this study, two methodologies are used: 1)

Literature review and 2) Simulation.

The literature reviews were conducted in order to determine what the challenges of

implementation of ERTMS are to resolve issues related to ERTMS subsystems (Global System

for Mobile Communication – Railway (GSM-R), and ETCS). ETCS needs to exploit hybrid

technologies for gradual deployment of next generation signalling systems. GSM-R must be

replaced with new technologies such as, long-term evolution (LTE) to support necessary data

transmission capacity for implementation of the next generation of signalling system.

Furthermore, the literature review regarding achieving interoperable and intelligent railway

transport shows that reducing wayside equipment have potential to provide a more cost-

efficient railway transport. To test and validate this finding, it is necessary to develop adapted

tools for railway and signalling systems. Providing flexible railway operation with backward-

forward interoperability and hybrid solutions will make it possible to gradually upgrade current

systems.

As decision-makers look for additional performance in new signalling systems over legacy

installations, the impact various signalling systems have on line capacity must be examined.

To this end, a comparative analysis between legacy ATC, ETCS Level 2, and ETCS Hybrid

Level 3 using simulation tool was performed. The case study was performed on a high

frequency traffic commuter train line in Stockholm during peak hours. The results of study show

HL3 delivers better performance compared to the legacy system and ETCS L2, and can deliver

acceptable performance for a commuter train line with high density. Considering the case

study, it can be concluded that HL3 delivers better performance on commuter train lines with

high density.

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Sammanfattning

Huvudsyftet med European Rail Traffic Management System (ERTMS) är att avlägsna

tekniska gränshinder och skapa ett driftskompatibelt järnvägsnät i europeiska länder (Smith et

al. 2012). Sedan dess tillkomst har ERTMS utsatts för prövningar i flera frågor om

interoperabilitet och implementering. Dessutom är en av huvudfrågorna för beslutsfattare och

infrastrukturförvaltare som hanterar ERTMS att bestämma vilken driftsnivå som är lämplig att

implementera och leverera ytterligare prestanda jämfört med äldre system.

Denna avhandling syftar till att identifiera utmaningar för ERTMS relaterade till implementering

och interoperabilitet för att uppnå ett mobilt och intelligent järnvägstransportsystem. I en studie

undersöks effekterna på kapaciteten av ERTMS Hybrid Level 3 (HL3) jämfört med European

Train Control System Level 2, (ETCS L2) och ett svenskt äldre system, ATC2. För att uppnå

målen för denna studie används två metoder: 1) Litteraturgenomgång och 2) Simulering.

Litteraturöversikterna genomfördes för att avgöra vilka utmaningar implementeringen av

ERTMS medför för att lösa problem relaterade till ERTMS delsystem (Global System for Mobile

Communication - Railway (GSM-R) och ETCS). ETCS behöver utnyttja hybridteknik för gradvis

användning av nästa generations signaleringssystem. GSM-R måste ersättas med ny teknik,

såsom långtidsutveckling (LTE) för att stödja nödvändig dataöverföringskapacitet för

implementering av nästa generations signaleringssystem.

Vidare visar litteraturöversikten om att uppnå interoperabla och intelligenta järnvägstransporter

att en minskning av utrustning i banan har potential att ge en mer kostnadseffektiva

järnvägstransporter. För att testa och validera detta är det nödvändigt att utveckla anpassade

verktyg för signalsystem för järnväg. Att åstadkomma flexibel järnvägstrafik med bakåt-framåt-

interoperabilitet och hybridlösningar kommer att göra det möjligt att gradvis uppgradera

nuvarande system.

Eftersom beslutsfattare letar efter ytterligare prestanda i nya signalsystem jämfört med äldre

system måste effekterna av olika signalsystem på linjekapaciteten undersökas. För detta

ändamål utfördes en jämförande analys mellan äldre ATC, ETCS nivå 2 och ETCS hybridnivå

3 med simuleringsverktyg. Fallstudien utfördes på en tättrafikerad pendeltågslinje i Stockholm

under högtrafikperiod. Resultaten av studien visar att HL3 ger bättre prestanda jämfört med

det äldre systemet och ETCS L2 och kan leverera acceptabla prestanda för en pendeltågslinje

med tät trafik. Med tanke på fallstudien kan man dra slutsatsen att HL3 ger bättre prestanda

på pendeltågslinjer med tät trafik.

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Acknowledgments

First of all, I want to thank Josef Malas at the Swedish Transport Administration (Trafikverket)

for funding my research, and Anders Lindahl at KTH for coordinating the project. I would also

like to heartily thank my supervisors Oskar Fröidh, Nils Olsson, Johan Silfwerbrand and Olov

Lindfeldt for all support and advice, and the knowledge and ideas you´ve shared with me.

And of course, a big thank you to my colleagues at KTH! Hasse Sipilä for all support concerning

simulation, capacity and timetabling. Thanks also to the rest of the rail planning group for

support, feedback and ideas.

Thanks to everybody I forgot to name here. And last but not least thanks to my family and

friends who supported me a lot. Especially my mother and brother supporting me in any

situation.

Stockholm, May 2021

Vahid Ranjbar

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Table of Contents

Papers and Declaration of Authorship ..................................................................................................... 1

Abstract .................................................................................................................................................... 2

Sammanfattning ...................................................................................................................................... 3

Acknowledgments ................................................................................................................................... 4

Acronyms ................................................................................................................................................. 6

List of figures ........................................................................................................................................... 7

List of tables............................................................................................................................................. 7

1 Introduction ...................................................................................................................................... 8

1.1 Background ...................................................................................................................................... 8

1.2 Problem definition ............................................................................................................................ 9

1.3 Objectives ........................................................................................................................................ 9

1.4 Research questions ....................................................................................................................... 10

1.5 Limitations ...................................................................................................................................... 10

2 Methodology .................................................................................................................................. 10

3 Results ........................................................................................................................................... 14

3.1 Paper I ........................................................................................................................................... 14

3.2 Paper II .......................................................................................................................................... 15

3.3 Paper III ......................................................................................................................................... 16

3.4 Scientific Contribution .................................................................................................................... 16

4 Conclusions ................................................................................................................................... 17

5 Future work .................................................................................................................................... 18

References ............................................................................................................................................ 19

List of errors ........................................................................................................................................... 21

6

Acronyms

BTM Balise Transmission Module

BIU Brake Interface Unit

DMI Driver Machine Interface

EC European Commission

ERTMS European Rail Traffic Management System

ETCS European Train Control System

EVC European Vital Computer

FRMCS Future Railway Mobile Communication System

GNSS Global Navigation Satellite Systems

GSM-R Global System for Mobile Communications – Railways

HL3 Hybrid Level 3

JUR Juridical Recorder Unit

LEU Line side Electronic Unit

LTE Long-Term Evolution

RBC Radio Block Centre

RQ Research Question

STM Specific Transmission Module

TIM Train Integrity Monitoring

TIU Train Interface Unit

TTD Trackside Train Detection

VC Vital Computer

VSS Virtual Sub-Section

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List of figures

Figure 1: Infrastructure model in Scenario 1 ......................................................................................... 11

Figure 2: Infrastructure model in Scenario 2 ......................................................................................... 12

Figure 3: Infrastructure model in Scenario 3 ......................................................................................... 12

Figure 4: Blocking time sequences ....................................................................................................... 13

Figure 5: Capacity Consumption with the compression method .......................................................... 14

List of tables

Table 1: Onboard Subsystem and related interfaces and components .................................................. 9

Table 2: Trackside Subsystem and related interfaces and components ................................................ 9

Table 3: Methodological guideline to answer RQ3 ................................................................................ 13

Table 4: Applied RQs and applied methodologies ................................................................................ 14

Table 5: Overview of reviewed literature focused on technical issues .................................................. 15

Table 6: The main themes and related critical issues of the reviewed literature .................................. 15

Table 7: Summary of results .................................................................................................................. 16

Table 8: Published papers based on RQs ............................................................................................. 16

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1 Introduction

The main aim of the European Rail Traffic Management System (ERTMS) is to create an

integrated railway network for European countries that is interconnected between railway

actors in various ways. This thesis covers both technological issues relating to ERTMS and

the impact of signalling systems on capacity using two methods: 1) Literature review 2) A

simulation tool (RailSys). The following subsections give a brief overview of background,

problem definition, objectives, research questions, and limitations.

1.1 Background

Over the years, several incompatible signalling systems have been developed in the railway

industry and used variously in different countries. This creates a costly obstacle for trains

crossing borders. Introduction of the European Rail Traffic Management System (ERTMS) is

now required by the European Commission. The main purpose of ERTMS is to remove cross-

border barriers and create a Single European Railway Area (SERA). Its harmonized standards

and technical specifications would contribute to enhance safety, reliability, lifecycle cost, and

performance for passenger and freight trains throughout the European railway network. SERA

would increase rail industry competitiveness (UIC, 2009).

ERTMS involves several components including trains and drivers, the Global System for

Mobile Communications – Railway (GSM-R) with mobile and fixed components, and the

European Train Control System (ETCS) (with both on-board and trackside subsystems),

(Młyńczak, et al. 2016; ERTMS User Group, 2016; Kornaszewski et al. 2017). All these interact

with the signalling system to create a complete Control Command and Signalling system

(CCSs). ETCS controls train operation along the line through continuous data exchange

between individual trains and track. GSM-R provides bidirectional communication of voice and

data between wayside subsystems and control centers.

High demand for railway transport has led to traffic congestion and near overload capacity in

some railway networks which can impact economic attractiveness (Abril et al., 2008). Due to

such limitations as high cost of infrastructure extension investments, and service interruption

because of upgrading, the railway industry is motivated to move towards digital, interoperable,

mobile, and intelligent solutions that replace fixed block technology with moving block and

virtual coupling systems to manage available capacity as best possible (Nold & Corman, 2021;

Flammini et al. 2018). In conventional signalling systems, drivers rely on wayside signals and

in-cab signalling systems that can display certain information depending on the technology

implemented. Fixed block technology means the track is divided into shorter block sections

which are protected by a main or block section signal for safety purposes. In moving block

technology with absolute braking distance, movement authority is based on length of train,

safety margin, and braking distance to the rear end of the train ahead (Pachl, 2002; ERTMS

Users Group, 2019). Implemented signalling systems along the railway considerably impact

capacity and stability of the line (Goverde et al., 2013).

Implementing advanced signalling systems such as ERTMS level 3 Full Moving Block requires

fulfilling certain prerequisites. These include equipping trains with Train Integrity Monitoring

(TIM) and a positioning system. This requires upgrading the entire fleet with TIM and a

positioning system over short period which may not be cost efficient.

In this situation, it is convenient to update the signalling system gradually by using hybrid

solutions such as ERTMS Level 3 Fixed Virtual Blocks, with Trackside Train Detection (TTD),

known as Hybrid Level 3 (HL3). HL3 allows trains fitted with the necessary equipment to run

on the same line as those not fitted (ERTMS Users Group, 2018). Maximum performance

would still be attained when all trains are equipped with TIM, while performance improvement

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would be correlated to the number of trains properly equipped with TIM (Furness et al. 2017).

In order to investigate the challenges of implementation and interoperability for ERTMS, two

separate structured literature reviews are conducted. To examine the impact of implementing

different signalling systems on capacity, a comparative analysis is performed using the

microscopic simulation tool RailSys.

1.2 Problem definition

For improvement in implementation of ERTMS and to overcome related challenges in the

future, it is necessary to identify key implementation issues based on lessons from previous

experience.

To enhance interoperable and mobile ERTMS, it is necessary to identify related issues, take

appropriate action, and eliminate the obstacles. In terms of implementing new technologies

such as moving block systems, the challenges related to Train Integrity Monitoring (TIM) and

to positioning systems plus the high cost of upgrading entire systems alternative solutions must

be identified. As capacity depends on several factors such as infrastructure and rolling stock

features, signalling systems, timetables, and their mutual interaction, the impact each

signalling system (and alternative solutions for legacy systems) has on capacity must also be

verified against an actual timetable. This will help to determine which signalling systems meet

decisionmaker’s needs when they consider replacing any legacy signalling system.

1.3 Objectives

The main objective of this study is to identify challenges to implementation and interoperability of ERTMS. After investigating these, the thesis focuses on the impact that suggested solutions for signalling systems have on different operating levels of the ETCS (primarily ETCS Level 2 and Hybrid Level 3 as compared to the Swedish legacy signalling system, ATC2). This compares capacity of the line (using capacity consumption as performance indicator) under unperturbed conditions based on an actual timetable. Tables 1 and 2 present the main components and interfaces, and the differences between onboard and trackside subsystems in HL3, ETCS and ATC2.

On-board Subsystem, components and interfaces

Level VC BTM BIU STM TIU TIM Odometry JUR DMI GSM-R

ETCS L2 -

HL3 *

ATC2 - -

Table 1: Onboard Subsystem and related interfaces and components (see list of abbreviations).

*HL3 allows train with and with TIM run on the same line.

Trackside subsystem and components

Level Trackside signal Track circuits/axle counter Balise Encoder (LEU) RBC GSM-R

ETCS L2 - -

HL3 - -

ATC2 - -

Table 2: Trackside Subsystem and related interfaces and components.

This study aims to investigate several issues: First, to identify the key challenges involved in

implementation of ERTMS; Second, it highlights problems related to achieving interoperable

railway transport; and finally, it explores whether hybrid level 3 (HL3) can deliver better

performance compared to ETCS L2 and the legacy ATC2 system.

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1.4 Research questions

Signalling systems are complex because they interact with subsystems which comprise

several types of equipment. To provide cost-efficient implementation, interoperable, and high-

performance rail operation identifying relevant issues to avoid in future using advanced

technologies is necessary. To analyse challenges related to implementation, interoperability,

and capacity performance the following research questions (RQs) are presented and

answered in this study:

• RQ1: Which are the challenges facing implementation of ERTMS?

• RQ2: Which are the challenges facing ERTMS to achieve an interoperable, mobile, and

intelligent railway transport?

• RQ3: Could a hybrid level 3 (HL3) system deliver better performance compared to a

legacy system or ETCS L2?

1.5 Limitations

In Papers I and II, to study issues regarding implementation and interoperability and related

technological issues, two separate extensive literature reviews are performed. The study for paper III is performed on a high-density commuter train line with homogeneous

traffic flow. The homogeneous traffic results in lower capacity consumption (higher

performance) compared to heterogeneous traffic (Goverde et al., 2013). To evaluate the

expected performance considering capacity consumption as performance indicator, the

analysis is performed based on an existing timetable under static conditions without

perturbations and probability functions. The field test for different scenarios has not been

performed. Instead, the microscopic simulation tool (RailSys) is used. The typical readers of

all three papers are railway engineering researchers and research interested practitioners.

2 Methodology

This thesis is based on two types of research methodologies: 1) Literature review 2) Evaluation

of capacity using a microscopic simulation tool. In general, simulation tools are categorized

into microscopic and macroscopic models. Microscopic tools consider the details of

infrastructure, vehicles, and timetable where macroscopic models are simplified and suitable

for network optimization (Borndörfer & Lamorgese, 2018; Johansson, 2021).

Strength of literature review covers openly available documentation and literature search is

possible to replicate by other researchers, because it is based on established and transparent

search methodologies. One disadvantage is that publications that are not openly available but

may include relevant information are not included. By only focusing on new publications it risks

that older publications contain valuable information, even though that information may be

outdated. Regarding the capacity evaluation with simulation one advantage is that is replicable

and it is easy to present results of study with graphs. As for disadvantages of microscopic

simulation, they are time consuming and require large amount of data to set up the complete

simulation.

In order to prevent similar issues in future, it is appropriate to identify the issues experienced

and the find solutions for future development. To identify challenges of implementation,

interoperability, and technology, a literature review covering lessons from previous experience

was performed. A literature review to identify technical issues facing implementation of ERTMS

was also carried out. The literature review started with running a key word “ERTMS” AND

“experiences” search in online research literature databases, as presented in tables in included

papers, to build an information pool, reducing the number of publications choosing scientific

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publications concerning technical issues relating to ERTMS implementation. The search was

not limited geographically. Further details of the study methodology and execution is presented in paper I.

Interoperability and removing obstacles for rolling stock crossing borders is a primary goal of

ERTMS (Schuitemaker & Rajabalinejad 2017). However, such interoperability throughout the

European railways has continually faced obstacles for several reasons. The second paper is

a literature review that briefly highlights several of these obstacles and related technological

challenges by analysing the current ERTMS architecture and primary concerns involving

implementation, interoperability of communication, formal methods, hybrid ERMS (Level 3), safety, and human factors. 82 papers were reviewed in this study. Paper II attempts to answer

the issues posed in RQ2 with this literature review that used the key words “ERTMS ISSUES”

and “ERTMS OPERATION” against online scientific databases.

The literature review contains publications from 2015 and later, which are categorised along

main themes, such as formal methods, adaptable communication systems¸ GNSS-based train

positioning, implementation of ERTMS, cyber security, safety, digitalisation, risk assessment

ERTMS, virtual coupling, human factors, interoperability and ERTMS Hybrid Level 3. For each

category, the most cited paper was chosen for closer reading and analysis. Paper II also

details the methodology applied. These main themes and related critical issues with proposed solutions are identified and presented in Tables 5 and 6. The literature study steps in papers I & II are as follows (Blumberg et al. 2004):

• Build information pool.

• Apply filter to reduce pool size.

• Rough assessment of sources.

• Reduce pool size.

• Analyse literature in pool.

After identifying the implementation and interoperability challenges based on results from

these studies (a tendency to implement hybrid solutions to gradually upgrade signalling

systems and interest in protentional performance gains) published in papers I & II, raises the

issues in RQ3. To answer RQ3 as stated – Could a hybrid level 3 (HL3) system deliver higher

performance compared to legacy systems and ETCS L2? – the impact these signalling

systems have on capacity is examined. The case study was conducted on a high density commuter line in Stockholm (paper III). This study started with a literature review over basic

concepts of capacity, capacity calculation methods and the previous studies that have been

carried out (Radtke & Hauptmann, 2004; Bendfeldt, 2000; Jansen, 2019). Then, using the

Swedish national RailSys model provided by Trafikverket, different scenarios were designed

to conduct a comparative analysis between the ATC2 legacy signalling system, ETCS L2 and

a new concept of ETCS Hybrid Level 3. The designed scenarios are as follows:

• Scenario 1 is based on current conditions with the legacy signalling system ATC2.

Figure 1: Infrastructure model in Scenario 1.

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• In scenario 2, the line and trains are upgraded to ERTMS/ETCS L2, signals are

replaced with marker boards but the location and length of the block sections remain

the same as in scenario 1.

Figure 2: Infrastructure model in Scenario 2.

• In scenario 3, the line is upgraded to HL3 assuming that the existing physical block

sections are divided into fixed subsections of a Virtual SubSection (VSS) that are 100

to 200 meters each).

Figure 3: Infrastructure model in Scenario 3.

Methods for capacity evaluation are classified into:

• Analytical

• Simulation.

The blocking time model is a straightforward analytical method introduced by Happel in 1959

to evaluate minimum headway. Currently, this model is applied in microscopic simulation tools

such as RailSys and OpenTrack to evaluate occupation time. This approach models the

blocking time sequences in detail and demonstrates the importance of signalling systems and

how they may impact capacity (Pachl & White, 2004; Hansen & Pachl, 2014). Figure 1 here

shows the minimum headway between two trains based on concept of blocking time

sequences.

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Figure 4: Blocking time sequences (Pachl & White, 2004).

In the RailSys simulation tool, the extracted data such as occupation time are based on minimum headway without considering a time supplement and buffer time. Paper III describes the study in more detail. Table 3 summarises the Methodological guidelines for answering RQ3.

Method Description

Study of signalling systems Using reports, technical specification of the system, and scientific literatures. Literature review on capacity, methods, and results

Review of the most cited publications using scientific data bases with master and PhD theses on the topic.

Setting up the simulation tool Based on the Trafikverket national RailSys model T20 designing different scenarios in order to evaluate headway and occupation time.

Extracting and processing data Processing extracted date to evaluate occupation time and capacity consumption, synthetizing and drawing conclusions.

Table 3: Methodological guideline to answer RQ3.

The configuration of simulation tool started from RailSys base model that is provided by Trafikverket (Swedish Transport Administration). The base model configured for scenario II and III based on assumptions above. Measuring occupation time, capacity consumption is calculated using the following formulas:

Occupation time [%] =Occupation Time

Defined time period∗ 100%

Capacity consumption [%] =Occupation Time + Additional time

Defined time period∗ 100%

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Figure 5: Capacity Consumption with the compression method (UIC, 2013).

The results of occupation times and capacity consumption are summarized in Table 7. Table 4 presents the defined research questions, papers, and methods mainly used in this thesis.

RQ Paper Method

RQ1: Which are the challenges facing implementation of ERTMS?

I. Vahid Ranjbar, Nils O E Olsson (2020) Development of future signalling systems - European Rail Traffic Management System (ERTMS) Presented at 8th Transport Research Arena, Helsinki, Finland Project

Structured literature review (Munn, et al. 2018)

RQ2: Which are the challenges facing ERTMS to achieve an interoperable, mobile, and intelligent railway transport?

II. Vahid Ranjbar, Nils O E Olsson (2020) TOWARDS MOBILE AND INTELLIGENT RAILWAY TRANSPORT: A REVIEW OF RECENT ERTMS RELATED RESEARCH

Structured literature review (Munn, et al. 2018)

RQ3: Could the HL3 system deliver better performance, compared to ETCS L2 or a legacy system?

III. Vahid Ranjbar, Nils O.E. Olsson, Hans Sipilä (2021) Impact of signalling system on capacity – Comparing legacy ATC, ETCS Level 2, and ETCS Hybrid Level 3 systems

Capacity analysis

Table 4: Applied RQs and applied methodologies.

3 Results

To answer the research questions in this licentiate thesis, three studies were carried out using two methods: Literature reviews and microscopic simulation. The following section presents the results of studies included in the papers. More details are found in the papers themselves.

3.1 Paper I

To investigate the challenges and current issues relating to implementation of ERTMS from the birth of this concept to the present, a systematic literature review was conducted where data were gathered and analysed, with the results published in the paper I. Looking into the research content, the study indicates a need to reduce complexity created by the many railway industry stakeholders, defining an integrated entity for conformity assessment, safety assessment, rolling stock, and implementation of wayside equipment. There is a gap in how drivers understand new technologies and an emphasis on familiarizing

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them with new technologies. To enhance bidirectional communication between the trackside and trains, and inter-train connections, it is necessary to migrate toward LTE and 5G technology, a modular approach, and hybrid solutions. The analysis indicates that reducing the number of components will lead to reduced cost and less complex systems.

Bibliography Level Driver On-board GSM-R Safety Positioning Integrity Flammini et al. 2018 2,3

Krmac & Djordjevii, 2019 1,2,3

Nachtigall & Ouředníček, 2018

2

Salvatori et al. 2018 - - -

Mehmetaj & Berisha, 2018 1,2,3 - - Schuitemaker & Rajabalinejad 2017

1,2,3 - - -

Mlinaric et al. 2017 1,2 - - - Canonico, et al.2017 - - - - Neri et al.,2017 - - - - - -

Table 5: Overview of reviewed literature focused on technical issues.

3.2 Paper II

To answer RQ2, after identifying the main issues these were categorized into issues based on i) literature review, ii) reducing the cost of implementation and maintenance, and iii) increasing interoperability. Findings show that is desireable to reduce the number of wayside components and pivot the system as a whole toward mobile equipment, autonomous trains, and decentralised communication. In the area of formalisation, it is necessary to develop a robust and reliable tool for more standardised modelling, formalisation, testing, and validation of critical safety systems specific to the needs of the railway industry for use by all involved parties. To reuse and build on earlier investment in ERTMS, it is necessary to pursue hybrid solutions and gradually update current systems in order to guarantee backwards and forwards interoperability. Table 6 presents the main themes and critical issues of the reviewed literature with proposed solutions.

Main theme Proposed solutions

Formal method Developing a universal formal method for signalling and interlocking (Basile D. et al. 2018).

Adaptable communication system Replacing GSM-R with new solutions, including LTE/4G, 5G or a hybrid system, to ensure interoperability with previous and future solutions (Canonico, et al. 2017; Mazzenga, et al. 2015).

GNSS-based train positioning For the calculation of potential hazardous situations, considering the principals of safety criteria of railway systems, hybridised architecture, and the calculation of potential hazardous situations (Beugin et al. 2018).

Implementation of ERTMS Step-by-step upgrading of the railway system (Kornaszewski, et al. 2017).

Cyber security Designing proper tools to guarantee the safety and dependability of Cyber-Physical Systems (CPS) (Armengaud, et al. 2018).

Safety Employing clear graphical presentation of safety data and predicted interactions between different data flows and software layers to effectively estimate risk (Gario, et al. 2018).

Digitalisation Equip trains and road vehicles with automatic protection systems (Tokody et al. Schuster 2017).

Risk assessment ERTMS Higher connectivity and a higher number of hazardous situations caused by electronic attacks require the improvement of security in connected systems (Bloomfield, et al. 2016).

Virtual coupling Replacing GSM-R with new communication systems (5G) (Flammini et al. 2018).

Human factors Training train drivers to address knowledge gaps between drivers and new train driving models (Naghiyev et al., 2017).

Interoperability Stabilise technical specification by a unique designer entity (Schuitemaker & Rajabalinejad 2017).

Hybrid ERTMS/ETCS Level 3 Guaranteeing operation without collision by hazard mitigation of the system (Hoang, et al. 2018).

Table 6: The main themes and related critical issues of the reviewed literature.

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3.3 Paper III

In order to verify the impact of different signalling systems on capacity, line comparative analysis on a commuter rail line in Stockholm is used to calculate differences using the microscopic simulation tool (RailSys). The case study was performed on a commuter rail line in Stockholm during peak hours. The defined time period was two hours (7200 s) in the afternoon between 4 and 6 p.m. on the southbound (Solna- Älvsjö). The summarized results are presented in Table 7. Capacity consumption is the proportion of occupation time plus additional time (for acceptable quality of service) to the defined time period.

Signalling system Occupation

Time [s]

Capacity

Consumption [%]

Minimum

Headway [s]

Ratio of Headway

(compared to ATC2)

ATC2 3090 51 104 100

ETCS L2 2805 46 94 90

HL3 2247 37 77 74

Table 7: Summary of results.

The results of this study show that, in total, ETCS L2 delivers 5% capacity gains and higher performance in comparison to ATC2. And that HL3 (with existing trackside train detection divided into VSSs between 100 to 200 meters) shows gains of 14% and 9%, respectively, in capacity and delivers higher performance compared to both ATC2 and ETCS L2.

3.4 Scientific Contribution

The thesis addresses both railway technological issues and the impact on capacity when

upgrading signalling systems.

This work contributes to identifying technological issues related to implementation and interoperability of ERTMS and its overall architecture to remove obstacles inhibiting a move towards mobile and intelligent railway transport. The research studies technological aspects with emphasis on overall system architecture and technologies included. As it is desirable for the system to be based on standard solutions with new technology that supports both current and future signalling needs based on capacity demands and operational railway traffic, the impact of different signalling systems on capacity was investigated. Table 8 presents the papers and RQs that are mainly related to technology and traffic, respectively.

RQ1 RQ2 RQ3

Technology Paper I Implementation

experiences

Paper II

Critical issues and

proposed solutions

Technology and operational

railway traffic

Paper III

Capacity for HL3

signalling

Contribution Identification of implementation challenges

for future enhancements

Identification of interoperability issues and

proposed solutions for

improvements

Impact of HL3 on capacity compared to

ETCS L2 and legacy

signalling system

Table 8: Published papers based on RQs.

Paper I. Ranjbar, V., & Olsson, N. O. E. (2020). Key challenges of European Rail traffic Management System. Proceedings of 8th Transport Research Arena TRA 2020, April 27-30, 2020, Helsinki, Finland. This study aimed to analyse key challenges to European Rail Traffic Management System (ERTMS) implementation encountered in recent years. And the identification of implementation challenges for future enhancements. After the identifying implementation challenges, it was necessary to verify technological obstacles for achieving an interoperable signalling system. RQ2 was designed to this end.

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Paper II. Ranjbar, V., & Olsson, N. O. E. (2020). Towards mobile and intelligent railway transport: A review of recent ERTMS related research. In Computers in Railways XVII (Vol. 1, pp. 65–73). WIT Press. This research contributed to investigate the challenges faced in developing interoperable signalling systems by analysing the current architecture of ERTMS and main technological concerns such as formal methods, adaptable communication systems¸ GNSS-based train positioning, implementation of ERTMS, cyber security, safety, digitalisation, risk assessment ERTMS, virtual coupling, human factors, interoperability, and Hybrid ERTMS/ETCS Level 3. This study connects theoretical advancements with hybrid signalling to the impact on capacity performance. The study concluded that in order to save costs and build on earlier investment in ERTMS, it is necessary to pursue hybrid solutions and gradually update current systems. In other words, gradual upgrade to the system can guarantee backwards and forwards interoperability. RQ3 was designed using this conclusion to consider the concerns of decision-makers relating to replacing legacy signalling systems with new technologies who must determine which solution provides the benefits they require.

Paper III. Ranjbar, V., Olsson, N.O.E, & Sipilä, H. (submitted to Journal of Rail Transport Planning & Management, 2021) Impact of signalling system on capacity – A case study comparing legacy ATC, ETCS Level 2 and ETCS Hybrid Level 3 systems on a high-density commuter line section. Considering the conclusions in paper II to address the interest decision-makers have in determining the signalling system that can provide the best performance, this study examines the impact ETCS HL3 has on capacity compared to ETCS L2 and a legacy signalling system. The study was performed on a high-density commuter train line in Stockholm. As this study was performed on a commuter rail line with homogeneous traffic without considering delays and under static conditions a future study could be to analyse capacity effects HL3 has on lines with heterogenous traffic under disturbance.

4 Conclusions

The European Commission decided to create an integrated railway area by introducing ERTMS in order to remove obstacles to making railway transport attractive and competitive. But implementing ERTMS in all European countries has faced a series of issues. Relating to RQ1 – “Which are the challenges facing implementation of ERTMS?” – a systematic literature review of the issues involved in implementing ERTMS was performed. To address issues related to reducing the excess numbers of stakeholders a centralized entity for regulation and safety assessment and implementation is necessary. Resolving technical issues involved in the subsystems in ERTMS, ETCS, and GSM-R should involve replacing GSM-R with a new high-capacity data transmission communication system. Further, to address the difficulties and short-term excessive expense involved in upgrading conventional signalling systems based on fixed block technologies to moving block technology, proposed hybrid solutions can help in a more gradual upgrade of legacy signalling systems. RQ2 addresses one the main ERTMS goals – to create interoperable railway systems throughout Europe and in other interested countries. This research question: “Which are the challenges facing ERTMS to achieve an interoperable, mobile, and intelligent railway transport?” required another systematic literature review. This review shows that several stakeholders involved have competing interests in any changes to the railway industry – presenting a significant challenge the introducing interoperability in ERTMS. Testing and validation of new ideas requires specific robust and reliable tools adapted to the railway industry. To fill gaps in general understanding and new technologies, operators and their employees need to develop additional competencies. To reuse earlier investment in ERTMS and allow a smooth transition towards a next generation signalling system (with moving block technology), hybrid solutions are proposed. This could also bring a reduction in the number of wayside components which would considerably contribute to further cost-efficiency in implementation, maintenance and operation of these systems for rail traffic.

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Wayside equipment components can be reduced in such an implementation of next generation signalling systems which would use radio communication enabling high capacity data transmission and moving block technology. However, these have prerequisites that have a greater short-term cost. This therefore speaks for the necessity of upgrading signalling systems using hybrid technologies that permit trains equipped with integrity monitoring systems to operate together with unequipped trains on the same line. Finally, in RQ3 asked “Could a hybrid level 3 (HL3) system deliver better performance compared to a legacy system or ETCS L2?”. For this, performance of hybrid systems must be verified, where this study conducted a comparative capacity analysis between ERTMS HL3, ERTMS L2, and the Swedish ATC2 legacy system. This comparative analysis used a microscopic simulation tool. The study considered a high-density commuter train line in Stockholm with homogeneous traffic under scheduled conditions based on a 2020 timetable. This used the Swedish national RailSys model provided by Trafikverket which is configured to a different signalling system. The study results show that in addition to the signalling system, the length of block sections and braking curves also have a considerable impact on line capacity. The restrictive braking curves imposed by ETCS L2 causes greater capacity consumption when braking curves reach end of movement authority. However, in total ETCS L2 enables lower headway and capacity consumption compared to the Swedish ATC2 system. Finally, ERTMS HL3 with an existing trackside train detection system and shortened block sections delivers lower block occupation time and capacity consumption and therefore higher performance compared to both ATC2 and ETCS L2. The conclusion of the study shows that HL3 has potential to improve capacity on railway networks.

5 Future work

The work presented in this licentiate thesis concentrates on three broad areas that present technological challenges to the implementation, and interoperability of ERTMS and how signalling systems impact line capacity. Two intensive literature reviews are performed to study these technological issues. Then, the impact of signalling systems on capacity was studied using a microscopic simulation tool without consideration of probability function in a static situation on a single rail line with heterogeneous traffic. System complexity in terms of number of wayside components is noted to considerably increase cost of implementation and maintenance in addition to interfering with the interoperability with products manufactured by other suppliers. Cost analysis of different configuration of signalling systems is recommended. The best solution for this issue is most likely to design a simpler architecture to reduce amount of trackside equipment which should reduce costs in implementation, maintenance, and operation. Still, railway industry experts recommend hybrid solutions. Such hybrid solutions have greater appeal to decision-makers or infrastructure managers since this provides operational flexibility allowing trains with and without TIM to run simultaneously and which also enables gradual upgrading to signalling systems instead of requiring implementing a complete moving technology at once. Considering these needs and methodologies used with specific conditions, future work should include study of:

• Proposals for simplification of system architecture to provide smoother migration towards the next generation signalling system.

• Analysing capacity effects of HL3 on lines with heterogenous traffic considering delays under perturbated conditions.

• Developing concept specifications for HL3 to optimize capacity effects.

• More research to overcome implementation and technical problems found in the literature studies.

• Analysis of non-technical aspects such as policies, economic incentives, politics, legal, standardization, sustainability and other issues.

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List of errors

I. Vahid Ranjbar, Nils O.E. Olsson (2020) Key challenges of European Rail traffic Management

System, (2020), Proceedings of 8th Transport Research Arena TRA 2020, April 27-30, 2020, Helsinki,

Finland

Page 1. Section “to be replaced with GSM-R” shall be replaced with “to replace GSM-R”.

Table text table 6: “… marked x “ shall be replaced with “… marked – “