Handling increased need of maintenance
to meet future freight demands
Deterioration and effective maintenance strategies for track
system and rail vehicles

Project report 2022:04 in MMS200 - Project in railway technology

JASEUNG LEE
OSKAR LIGMAJER
KLARA MATTSSON

DEPARTMENT OF MECHANICS AND MARITIME SCIENCES (M2)

CHALMERS UNIVERSITY OF TECHNOLOGY
Gothenburg, Sweden 2022
www.chalmers.se

www.chalmers.se




Project report 2022:04

Handling increased need of maintenance
to meet future freight demands

Deterioration and effective maintenance strategies
for track system and rail vehicles

JASEUNG LEE
OSKAR LIGMAJER
KLARA MATTSSON

Department of Mechanics and Maritime Sciences (M2)
Division of Dynamics

The National Centre of Excellence in Railway Mechanics, CHARMEC
Chalmers University of Technology

Gothenburg, Sweden 2022



Handling increased need of maintenance to meet future freight demands
Deterioration and effective maintenance strategies for track system and rail vehicles
JASEUNG LEE, OSKAR LIGMAJER, KLARA MATTSSON
MMS200 - Project in railway technology 2022

© JASEUNG LEE, 2022.
© OSKAR LIGMAJER, 2022.
© KLARA MATTSSON, 2022.

Supervisor: Anders Ekberg, Department of Mechanics and Maritime Sciences (M2)
Examiner: Elena Kabo, Department of Mechanics and Maritime Sciences (M2)

Project report 2022:04
Department of Mechanics and Maritime Sciences
Division of Dynamics
The National Centre of Excellence in Railway Mechanics, CHARMEC
Chalmers University of Technology
SE-412 96 Gothenburg
Telephone +46 31 772 1000

Cover: Shunting of freight wagons at a railway station in Sweden. Figure by the
authors.

Typeset in LATEX, template by Kyriaki Antoniadou-Plytaria
Printed by Chalmers Reproservice
Gothenburg, Sweden 2022

iv



Handling increased need of maintenance to meet future freight demands
Deterioration and effective maintenance strategies for track system and rail vehicles
JASEUNG LEE, OSKAR LIGMAJER, KLARA MATTSSON
Project report 2022:04
Department of Mechanics and Maritime Sciences (M2)
Chalmers University of Technology

Summary
This report addresses future increased demands of freight on the Swedish railways.
To achieve an increase in total freight, different forms of operations can be utilized
like increasing the axle load, speed, or frequency which are all scenarios that will
be evaluated in the report. The impact caused by those measures will affect both
deterioration and the need for efficient maintenance regarding rail vehicles and track
systems. Different methods of maintenance, both currently used and newly devel-
oped methods are discussed in this report to be able to evaluate how it is possible to
become more efficient. The deterioration that occurs during the operation of freight
trains is described in the report since an understanding is needed to address the
problems and possible solutions. What also plays a vital role in the maintenance
plan is to detect faults efficiently. To get an idea about how all of these issues
are handled in the industry, interviews have been held with professional staff at
four large companies in Sweden. Together with literature studies, this forms the
foundation of this report.

Keywords: railway, deterioration, maintenance, track, vehicles, freight

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Acknowledgements
We are very thankful to our supervisor Anders Ekberg, Professor at Mechanics and
Maritime Sciences, Division of Dynamics, Chalmers University of Technology. He
has been very supportive of this project with his time and guidelines. We would
also like to thank our examiner Elena Kabo, Research Professor at Mechanics and
Maritime Sciences, Division of Dynamics, Chalmers University of Technology. She
has encouraged us to be positive and helped the authors. The supervisor and ex-
aminer’s sincere advice have led us to document and publish this report.

We would like to extend our appreciation to the railway industry personnel, who took
their time for interviews. Their experiences and insights have contributed to our
report significantly. Based on their answers, the authors could understand current
practices in the railway industry and how to better support and improve railway
maintenance engineering. In this regard, we are deeply thankful to Björn Nordh,
Håkan Larsson and Anders Dahlqvist at Green Cargo, Ivan Nalovski at Atkins,
Robert Pallari at LKAB and Per-Olof Larsson Kråik at Trafikverket, Sweden.

The authors in Göteborg, May 2022

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Table of contents

1 Introduction 1
1.1 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.2 Problem definition and research questions . . . . . . . . . . . . . . . 1

1.2.1 Problem definition . . . . . . . . . . . . . . . . . . . . . . . . 2
1.2.2 Research questions . . . . . . . . . . . . . . . . . . . . . . . . 2

1.3 Interviews . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
1.4 Alternative ways to increase freight traffic . . . . . . . . . . . . . . . 3

1.4.1 Significantly higher capacity . . . . . . . . . . . . . . . . . . . 3
1.4.2 Upgrading of existing lines . . . . . . . . . . . . . . . . . . . . 4
1.4.3 Some challenges beside deterioration and maintenance . . . . 5

1.4.3.1 Utilisation of the upgrade . . . . . . . . . . . . . . . 5
1.4.3.2 Interplay with passenger traffic . . . . . . . . . . . . 6
1.4.3.3 Longitudinal forces in the train . . . . . . . . . . . . 6
1.4.3.4 Parking spaces and handling of wagons . . . . . . . . 6

1.5 Limitations in research . . . . . . . . . . . . . . . . . . . . . . . . . . 6

2 Deterioration 9
2.1 Deterioration mechanisms . . . . . . . . . . . . . . . . . . . . . . . . 9
2.2 Track system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

2.2.1 Rails . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
2.2.2 Rail joints . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
2.2.3 Switches and crossings . . . . . . . . . . . . . . . . . . . . . . 11
2.2.4 Rail fastenings . . . . . . . . . . . . . . . . . . . . . . . . . . 11
2.2.5 Sleepers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
2.2.6 Ballast . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
2.2.7 Catenary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

2.3 Rail vehicles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
2.3.1 Wheels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
2.3.2 Axles and bearing boxes . . . . . . . . . . . . . . . . . . . . . 12
2.3.3 Brakes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
2.3.4 Springs and dampers . . . . . . . . . . . . . . . . . . . . . . . 13
2.3.5 Buffers and couplers . . . . . . . . . . . . . . . . . . . . . . . 14
2.3.6 Pantographs . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

2.4 Modelling of deterioration . . . . . . . . . . . . . . . . . . . . . . . . 14
2.4.1 Deterioration models . . . . . . . . . . . . . . . . . . . . . . . 14
2.4.2 Track system . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

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Table of contents

2.4.3 Rail vehicles . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

3 Maintenance actions 17
3.1 Track system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

3.1.1 Detecting faults . . . . . . . . . . . . . . . . . . . . . . . . . . 18
3.1.2 Maintenance measures . . . . . . . . . . . . . . . . . . . . . . 19
3.1.3 Challenges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

3.2 Rail vehicles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
3.2.1 Detecting faults . . . . . . . . . . . . . . . . . . . . . . . . . . 21

3.2.1.1 Track based detection . . . . . . . . . . . . . . . . . 21
3.2.1.2 Workshop based detection . . . . . . . . . . . . . . . 21

3.2.2 Maintenance measures . . . . . . . . . . . . . . . . . . . . . . 22
3.2.3 Challenges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

3.3 Effect of increasing demands on maintenance . . . . . . . . . . . . . . 23

4 Decreasing needs of maintenance 25
4.1 Track system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

4.1.1 Ballasted and slab track . . . . . . . . . . . . . . . . . . . . . 25
4.1.2 Rails . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
4.1.3 Managing friction forces . . . . . . . . . . . . . . . . . . . . . 25

4.2 Rail vehicles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
4.2.1 Tare mass . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
4.2.2 Rigid-frame and bogie wagons . . . . . . . . . . . . . . . . . . 26
4.2.3 Angle of attack . . . . . . . . . . . . . . . . . . . . . . . . . . 26
4.2.4 Tread and disc brakes . . . . . . . . . . . . . . . . . . . . . . 27
4.2.5 Material of brakes . . . . . . . . . . . . . . . . . . . . . . . . . 27
4.2.6 Managing locked wheels . . . . . . . . . . . . . . . . . . . . . 27

4.3 Avoiding complexity . . . . . . . . . . . . . . . . . . . . . . . . . . . 27

5 More efficient maintenance 29
5.1 Maintenance strategies for increasing demands . . . . . . . . . . . . . 29

5.1.1 Stricter maintenance intervention . . . . . . . . . . . . . . . . 29
5.1.2 Field maintenance outside workshop . . . . . . . . . . . . . . 29

5.2 Automation and digitalisation . . . . . . . . . . . . . . . . . . . . . . 30
5.2.1 Digital twin . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30

5.2.1.1 Simulation . . . . . . . . . . . . . . . . . . . . . . . 30
5.2.1.2 Prediction . . . . . . . . . . . . . . . . . . . . . . . . 30
5.2.1.3 Safety and efficiency . . . . . . . . . . . . . . . . . . 30

5.2.2 Maintenance planning . . . . . . . . . . . . . . . . . . . . . . 30
5.2.2.1 Condition based maintenance . . . . . . . . . . . . . 31
5.2.2.2 Predictive maintenance . . . . . . . . . . . . . . . . 31

5.2.3 Drawbacks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
5.2.3.1 Vulnerability . . . . . . . . . . . . . . . . . . . . . . 31
5.2.3.2 Complexity . . . . . . . . . . . . . . . . . . . . . . . 31
5.2.3.3 Amount and quality of data . . . . . . . . . . . . . . 32

5.3 Simplify for maintenance . . . . . . . . . . . . . . . . . . . . . . . . . 32
5.3.1 Design for maintenance . . . . . . . . . . . . . . . . . . . . . . 32

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Table of contents

5.3.2 Modularisation . . . . . . . . . . . . . . . . . . . . . . . . . . 32
5.3.3 Standardisation . . . . . . . . . . . . . . . . . . . . . . . . . . 33

5.4 Track system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
5.4.1 High speed measuring . . . . . . . . . . . . . . . . . . . . . . 33
5.4.2 Measuring with locomotives . . . . . . . . . . . . . . . . . . . 33
5.4.3 High speed grinding . . . . . . . . . . . . . . . . . . . . . . . 33

5.5 Rail vehicles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
5.5.1 Change in maintenance plans . . . . . . . . . . . . . . . . . . 33
5.5.2 Collect maintenance needs . . . . . . . . . . . . . . . . . . . . 33
5.5.3 Increase preventive maintenance . . . . . . . . . . . . . . . . . 34

6 Conclusions and future recommendations 35

References 37

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xii



1
Introduction

1.1 Background

The global energy system is in a transforming phase of becoming more sustainable
and Sweden has the goal of zero net emissions of greenhouse gases by 2045 [1]. One
important technique which will help to achieve this is using bio-energy with carbon
capture and storage. This technique captures the carbon dioxide from renewable
sources and stores it permanently.

Transportation of CO2 will be necessary to achieve this and rail freight transport
will play a vital role. This means an increase in the amount of total cargo on the
Swedish railway, which besides many opportunities also comes with complications.
This report will focus on how this increase in traffic on the railway can affect the
deterioration, both when it comes to the rail system and the vehicles. It will also
focus on the maintenance actions required to handle the increase.

Rail transportation in Sweden is already used to a large extent today, the amount
of freight transported by rail was 22 222 million tonne-kilometer in 2019 [2]. In the
same year the percentage of the total inland freight transport in Sweden measured
in tonne-kilometers, was 30.6% by rail [3]. A company which was interviewed during
this project is Green Cargo, they estimate that transport of CO2 can increase their
transported volume by 50%.

1.2 Problem definition and research questions

With an increase in freight train demands the loading weight on train and track
will increase. As a consequence, this will accelerate deterioration rates of track
systems and rail vehicles. Thus, malfunctioning tracks and vehicles on operations
may increase. Such problems will disrupt efficient transport of goods and hence add
more logistics costs. However, to meet the increasing freight demands, there could
be shortage of time and personnel for maintenance and reparation. It is therefore
important for freight train transport to handle the increased deterioration and set
operational strategies in an efficient and successful way [4].

1



1. Introduction

1.2.1 Problem definition
This study defines the problem as two following questions:

• How increasing freight volumes affect required maintenance actions?

• What maintenance strategies that are recommended?

1.2.2 Research questions
To fulfil the objectives of the research, the following questions can be answered:

• What deterioration mechanisms and maintenance actions for infrastructure
and vehicles will be affected?
This is mainly presented in Chapter 2 and Chapter 3.

• Is the increase in maintenance demands expected to be linear or exponential
in transport volumes?
This is mainly presented in Chapter 2.

• How can adverse effects be minimized by decreasing maintenance needs and/or
introducing more efficient maintenance?
This is mainly presented in Chapter 4 and Chapter 5.

• How would this roughly affect the availability of track and vehicles?
This is presented in various sections.

• What is the main challenges and most promising approaches?
This is mainly presented in Chapter 6.

• Is the increase in capacity feasible from a maintenance perspective?
This is mainly presented in Chapter 6.

1.3 Interviews
To get input from professional staff in the railway sector, four interviews were held.
The industrial companies that were interviewed are active in slightly different areas.

• Atkins
Is among other things a rail consultancy. The focus during this interview was
mainly planning and problems with maintenance and deterioration of wagons.

• Green Cargo
Is a rail freight operator. The focus during this interview was mainly the need
of increased freight capacity, and planning and problems with maintenance

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1. Introduction

and deterioration of locomotives and wagons.

• LKAB
Is a mining company. The focus during this interview was mainly planning
and problems with maintenance and deterioration of wagons.

• Trafikverket
Is an infrastructure manager. The focus during this interview was mainly
planning and problems with maintenance and deterioration of track.

1.4 Alternative ways to increase freight traffic
It is desired to achieve the most of every train operation, but there are constraints
in the power of the locomotive, the axle load, the loading gauge and the length of
the train. The number of train operations is constrained to the available time slots
of the track.

1.4.1 Significantly higher capacity
When it comes to increasing the capacity, some things should first be mentioned.

• Multiple track lines
The capacity of multiple track lines is significantly higher than for single track
because trains can travel more undisturbed in each direction at the same time.

In Sweden there are 10 909 km of trafficked track whereof 2 056 km are double
or multiple track [5]. Trains on single track that travel in the opposite direc-
tion have to meet at meeting points to be able to pass each other, while they
on double track can travel undisturbed from each other in both direction. One
step to increase the freight can therefore be to build double track where single
track is present today.

Another advantage with double track, compared to single track, is that the
maintenance work can be done at one of the tracks at a time, meaning that
the traffic can be redirected and continued on the other track.

• Uniform traffic
The capacity of uniform traffic is significantly higher than for non-uniform
traffic because passenger and freight trains can travel more frequently and
undisturbed from each other.

In Sweden there is a mixed traffic situation with faster passenger trains and
slower freight trains sharing the same track [6]. Passenger trains can have
speeds up to 200 km/h [7] while freight trains can have speeds up to 120 km/h
if they are unloaded [8]. Freight trains in un-uniform traffic may need to be

3



1. Introduction

put on side tracks for passenger trains to be able to pass them, while they
in uniform traffic can travel undisturbed from each other in their own pace.
The frequency of train operations can also be increased with uniform traffic
since the speeds of the trains then are more equal. One step to increase the
freight can therefore be to keep the passenger and freight traffic apart. This
can for example be done by having dedicated lines for one type of traffic or by
building quadruple track.

Another advantage with separate traffic is that the freight trains do not have
to be put on side tracks for passenger trains to pass, meaning that the energy
usage and wear on wheels and brakes from starts and stops of heavy freight
trains can be reduced [8].

However, such upgrades are very costly and also space and time consuming.

1.4.2 Upgrading of existing lines
Most of the new railway lines that are built today around the globe are constructed
for high speed or regional passenger traffic. Upgrading of existing lines is a more
common way to increase the freight capacity. It is therefore important with efficient
methods and means to be able to meet the higher demands [4].

There are various other ways to increase the total accumulated tonnes at the Swedish
railway. Some of them will be presented here together with some of their practical
needs in order to be feasible.

• Increased axle load of wagons
The increase in freight is obtained by loading more weight on the wagons of
the train, leading to an increased axle load while the length of the train, the
loading gauge of the wagons and the frequency of train operations are kept
unchanged.

To be able to increase the axle load, the track needs to be upgraded with
sufficient components. Also, for example bridges and culverts may need to be
redesigned. The standard axle load in Sweden is today 22.5 tonnes, and often
25 tonnes [6]. Some lines in the north of Sweden have an axle load of 30 tonnes
and aims to increase it to 32.5 tonnes. The wagons then need to be upgraded
with running gear suitable for the higher axle loads [9].

• Increased length of trains
The increase in freight is obtained by connecting more, or longer, wagons to
the train.

To be able to increase the length of the trains on single track, the meeting
points need to be lengthened for the trains to be able to pass each other. The
meeting points are today set from 450 metres up to 750 metres in Sweden. On

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1. Introduction

multiple tracks, such as double track, it is not the same problem with longer
trains out on the line as it is on single tracks [6].

• Increased loading gauge of wagons
The increase in freight is obtained by loading more volume on the bulkier wag-
ons of the train.

To be able to increase the loading gauge, the surrounding infrastructure have
to be redesigned. The Swedish gauging principles were defined 1893, but have
been updated more recently. It would be very costly and create difficulties to
change load profiles since it will affect the existing infrastructure and vehicles
[10]. For example, the distance between the tracks on double track may need
to be increased and tunnels may need to be redesigned.

• Increased frequency of train operations
The increase in freight is obtained by driving more separate trains.

To be able to increase the frequency, there must be available time slots that
work with the infrastructure. This is a consequence of the mixed traffic situa-
tion in Sweden. If more freight trains operations are to be done, the track will
be more crowded and more time slots will be occupied leading to a harder in-
terplay with the passenger trains. For example, the number of meeting points
may need to be increased. There will also be less time slots for track mainte-
nance.

An increase in freight can of course also be a combination of those alternatives. The
alternatives can also be combined with an increased speed, and this can especially
be desired with an increased frequency of train operations.

1.4.3 Some challenges beside deterioration and maintenance

The different alternatives in Chapter 1.4.2 have some important challenges beside
deterioration and maintenance. Challenges regarding the deterioration and mainte-
nance will be covered more later in the report.

1.4.3.1 Utilisation of the upgrade

It is important that it is possible to utilise the upgrade in a good way for it to increase
the total accumulated tonnes. For example, for low density goods an increased axle
load may not be sufficient since the goods already occupies a big part of the loading
gauge. In that case an increased loading gauge or train length would probably be
more efficient. On the other hand, an increased axle load can be sufficient for high
density goods, while an increased loading gauge may not be.

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1. Introduction

1.4.3.2 Interplay with passenger traffic

The passenger traffic will be disrupted with more, long, heavy and slow freight
trains. Combining the alternatives with higher speed will lower the time on track
and make the interplay with passenger trains better, especially if the frequency of
freight train operations is increased. It will also be more time available for track
maintenance, although the increased time available for track maintenance may not
be corresponding to the increased need of maintenance that comes with the higher
speed.

1.4.3.3 Longitudinal forces in the train

With heavier trains, both higher axle load and longer train, the tonnage is increased.
The couples further back of the train will get more load which can cause unwanted
dynamic longitudinal forces in the train. The locomotive should also be driven in
a different way to manage the increase in load, and length, making the skill of the
driver more important [8].

The brake systems on freight trains are usually pneumatic and controlled by pressure
variations through a main brake pipe. The pressure drop, that brakes the wagons,
propagates from the front of the train to the back. If it is not correctly arranged in
a smooth way it can lead to that unbraked wagons in the back of the train push on
braked wagons in front. This can give longitudinal forces that can lead to lifting of
wagons in long and heavy freight trains [11].

1.4.3.4 Parking spaces and handling of wagons

Higher axle loads limits the need for more parking space since the amount of wagons
can remain the same. This also limits the number of wagons that have to be handled
with loading, unloading, shunting and maintenance. However, an increase in the
amount of wagons may be needed with an increase in the train length and the
number of train operations. This will result in a need of more space at shunting
yards and at parking tracks near workshops, as well as more wagons have to be
handled.

1.5 Limitations in research
The limitations of the research are as follows:

• Only an increase of the rail freight in Sweden will be investigated.

• Life cycle cost assessment will not be considered or discussed at any large ex-
tent, although it is very vital and plays a major roll in decision making.

• An increase of freight will only be investigated for pure upgrade alternatives,
see Chapter 1.4.2, meaning that combinations of those will be left aside.

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1. Introduction

• An increase in loading gauge, see Chapter 1.4.2, will not be investigated as it
will not independently affect the deterioration of track and vehicle.

• The investigation will be quite broad and general, it will not be focusing on
specific items such as bridges and tunnels.

7



1. Introduction

8



2
Deterioration

2.1 Deterioration mechanisms
Plastic deformation
The meaning of plastic deformation is permanent deformations in a solid body. In
the railway field, plastic deformation can mainly be caused by contact load between
track surface and wheels. For instance, tracks on the iron ore transport line expe-
rience a load higher than 250 kN in a small contact area of 80-200 mm2. The high
stress loading generates plastic deformation on the railhead [11].

Wear
Wear constitutes gradual material removal due to contact and sliding motion. Rolling
wheels on tracks generate slip with high contact loads. The slip between rolling
wheel and track wear rail head as shown in Figure 2.1. Since wear changes wheel–
rail contact geometry, it can lead to contact stress increases, resulting in faster track
deterioration. Magnitude of contact load, slip, and rail hardness determine wear
rates of track. Wear can also occur in the ballast, which can cause track geometry
irregularities.

Figure 2.1: Railhead geometry with wear. Figure from [12].

Fatigue
Fatigue is deterioration phenomenon which appears in solid bodies exposed to high
alternating load. Rolling contact loads on track and wheels lead to fatigue in rail
operations. One of key points in fatigue is that it is a threshold phenomenon. When

9



2. Deterioration

load (stress) amplitude exceeds a fatigue limit, fatigue lives exponentially decrease
as shown in Figure 2.2.

Figure 2.2: Fatigue life S-N curve. Figure from [13].

2.2 Track system
Track components suffer from deterioration due to track forces and creep. The
deterioration rate of the track is decided by the total forces acting on the track [11].

2.2.1 Rails
Rolling contact fatigue occurs near the contact patch between vehicle and track
while plain fatigue occurs further away from the contact patch. Plain fatigue usu-
ally occurs near the rail foot or the lower corner of the rail head where cracks can
grow from defects and stress concentrations [14].

High normal and tangential stresses can cause head checks on the rail surface, and
together with high dynamic stresses from local irregularities can local cracking,
so-called squats, occur. Longitudinal cavities inside the rail head can cause tache
ovals, but due to today’s steel production they only sometimes occur near welds [11].

Due to the contact forces and the creep forces in curves, gauge corner wear occurs
on the outer rail while top surface wear occurs on the inner rail. The track gauge is
increased with gauge corner wear [11].

Plastic deformation can occur due to high loading close to free edges and severe
contact geometry. The material will be redistributed as well as residual stresses and
anisotropy can occur. It can also cause crack initiation [16].

10



2. Deterioration

2.2.2 Rail joints
Continuously welded rails are today common. Tensile residual stresses and phase
transformations are usually induced in the welding process. It can speed up fatigue
deterioration, and may together with material impurities and high load from poor
welding cause cracks, and in worse case detachment of the rail [14].

To insulate rail sections electrically, insulated joints are usually used together with
continuously welded rails [14]. An older method for connecting rails, and a method
for insulating rails, is with fish plates and bolts. This type of rail joint is a weak spot
since it is less stiff and contains a gap between the connected rails. The wheels dip
down when going over the joint due to the weakness and the gap, and this leads to
high dynamic forces affecting both the wheels and the rails [11]. Plastic deformation
can therefore occur at the joint which can lead to bridging , so-called lipping, at the
rail head over the gap [14].

2.2.3 Switches and crossings
Switches and crossings need to handle different shapes of wheel profiles and the wear
state of the wheel will affect the loading. The stresses can be high at switches and
crossings which can cause plastic deformation and cracking at for example switch
blades and crossing noses. There are also large relative motions between the wheels
and the rail at switches and crossings which can cause wear at for example switch
tongues and crossing noses [16].

2.2.4 Rail fastenings
The repeated loads from trains can lead to deterioration of the rail pads [11]. Insuf-
ficient fastening, due to cracking and detachment, can occur if the rail fastening is
subjected to high loads or due to wear of the rail pad [14].

2.2.5 Sleepers
The repeated loads from trains can lead to cracks in sleepers [11]. The cracks can
occur and grow from the geometrical irregularities near the fastening holes where
the stresses are high. Out-of-round wheels, together with, for example, a high axle
load can cause a high impact load on the sleeper that causes it to crack. The ballast
support will influence the location of the cracking of the sleeper. With proper ballast
support it can be prevented that cracks form in the middle of the sleeper where it
is weak [14].

If sleepers and rail fastenings do not work properly it can affect the transferring
of loads as well as affect the track gauge. Concrete sleepers are the most common
type on the mainlines in Europe and Sweden, but wooden sleepers are still in use in
many places [11]. Concrete sleepers provide good stability and have a long service
life, while wooden sleepers provide good elasticity and insulation [15]. Ballasted
track with concrete sleepers can be seen in Figure 2.3.

11



2. Deterioration

Figure 2.3: Ballasted track with concrete sleepers. Figure by the authors.

2.2.6 Ballast
The deformation and vibration from train movements can cause ballast wear [11],
and in severe cases cracked ballast stones. This will influence the function of the
ballast since the internal stiffness is decreased. Further, wear particles change the
stiffness and resistance ability of the ballast. The deformation and vibration from
train movements can also gradually lead to ballast settlements [14].

2.2.7 Catenary
The contact wire will wear due to the contact with the pantograph on electric trains
[8]. The contact can also cause the catenary to fatigue.

2.3 Rail vehicles
Vehicle components suffer from deterioration due to track forces and creep. High
impact forces, and vibrations, between wheel and rail can occur due to track defects.
This can lead to further damage on both track and wheel [11].

2.3.1 Wheels
Due to the contact forces and the creep forces in curves, together with the wheel
angle of attack, tread wear occurs on the inner wheel while flange wear occurs on
the outer wheel. High normal and tangential stresses can cause a phenomena on the
wheel that corresponds to formation of head checks on the rail. The wheels can also
become eccentric due to poor centering during profiling [11].

See also Chapter 2.3.3 for how brakes affect the deterioration of wheels.

2.3.2 Axles and bearing boxes
High load magnitudes can cause the bearing box to deteriorate which leads to heat
that melts the axle. An axle can also break due to plain fatigue caused by corrosion
on the axle [17].

12



2. Deterioration

2.3.3 Brakes

It is common with brake blocks that act on the wheel tread on freight wagons.
When the brake block is applied, the wheel tread is roughened. In addition, the
wheel can crack due to thermal overloading from the heat energy that is generated.
Out-of-round wheels, like wheels with a wheel flat, can occur if the wheel is locked
during braking and slides on the rail that also gets affected. Corrugation can arise
on the wheel tread during braking when some parts expand and wear due to a higher
temperature [11].

Brake blocks and wheels wear when pressed against each other. The respective
deterioration rate depends on the material of the brake pads. Brake blocks can for
example be made of cast iron, composite materials or be sintered [10]. Brake blocks
can be seen in Figure 2.4.

Figure 2.4: Brake blocks. Figure by the authors.

2.3.4 Springs and dampers

Suspension in freight wagons need to handle large variations in payload, since the
wagons can be everything from empty to fully loaded. Springs are used to make
the vehicle smoother and more isolated to forces on the track [10]. Some common
springs on freight wagons are rubber springs of the chevron type, coil springs and
leaf springs. The repeated loads that the springs suffer from can cause them to wear
and fatigue.

Dampers are used to limit the dynamic motions of the vehicle. Friction dampers get
wear on the friction surfaces but they are simple, cheap and robust, and are therefore
often used on freight wagons. The friction between the leaves in a leaf spring allows
the leaf spring to serve as both a spring and a damper. Rubber springs can provide
a damping effect while coil springs give almost no damping [10]. A bogie with leaf
springs can be seen in Figure 2.5.

13



2. Deterioration

Figure 2.5: Bogie with leaf springs. Figure by the authors.

2.3.5 Buffers and couplers

The buffers and couplers can wear because of the dynamics within the train [8]. The
repeated loads can cause the buffers and couplers to fatigue.

2.3.6 Pantographs

The pantograph on electric trains will wear due to the contact with the contact wire
[8]. The contact can also cause the pantograph to fatigue.

2.4 Modelling of deterioration

2.4.1 Deterioration models

The rate of deterioration mechanism such as wear, fatigue, and crack depend on
the level of the external load. Basically, each deterioration has own threshold and
it increases exponentially over the limit. However, deterioration rate is quite slow
with small variation of loads. The exponential characteristics may be approximated
as linear as shown in Figure 2.6.

Figure 2.6: General deterioration curve over load. Figure by the authors.

14



2. Deterioration

2.4.2 Track system

Linear model
The first step to model track deterioration assumes that it is proportional to amount
of tonnage that passes by the track as follows:

DQ = k1 × P (2.1)

in which DQ is a degradation of track quality, P is tonnage on track, usually mea-
sured as Million Gross Tonnage (MGT), the coefficient, k1 is determined from track
and vehicle operating conditions [18].

Exponential model
The above linear approximation is applicable with a small variation of loads. How-
ever, the track deterioration generally shows exponential behavior as a whole. An
exponential model for track quality over time can be expressed as follows:

Q(t) = Q0 × ebt (2.2)

Here Q0 is initial quality of infrastructure, b is the deterioration rate and t is en-
lapsed time. The exponential term, ebt describes rate of quality degradation over
a longer period [19]. It shows that track quality degrades faster over time without
proper maintenance action. Therefore, it is important to forecast future mainte-
nance demands based on trend analysis of train transport.

Deterioration law model
Another quantitative method to estimate track deterioration as function of tonnages,
axle load, and train speed is expressed as follows:

E = k × Tα × P β × V γ (2.3)

where E is deterioration, T is tonnage, P is axle load, and V is speed. α, β, and γ are
constants which represent the exponential effect of load parameters on deterioration
rates [20].

2.4.3 Rail vehicles

Wheel axle
The life time analysis of railway wheel axle can be based on studies of dependency
between number of load cycles and fatigue crack length [21]. The crack growth of
the wheel axle shows an exponential increase above a threshold load level, shown in
figure 2.7.

15



2. Deterioration

Figure 2.7: Dependency between fatigue crack length and load. Figure from [21].

Bearing
SKF (Svenska Kullagerfabriken, Swedish ball bearing factory) estimates bearing life
using a rating life formula as follows:

Lnm = a1 aSKF (C
P

)b (2.4)

where the Lnm is bearing rating life [millions of revolution], a1 is the life adjustment
factor for reliability, aSKF is life modification factor, C is the basic dynamic load
rating [kN], P is equivalent dynamic bearing load [kN], and b the exponent of the
life equation [22].

According to the the above formula, dynamic loading of the bearing significantly
affects the bearing life. In other words, both axle load and dynamic impact due to
track condition influence the bearing life.

Wheel wear
In the interview with LKAB [9], it was stated that 80% of their costs were due to
wheel maintenance. The maintenance carried out on the wheels is usually reprofiling.
Reprofiling of wheels mainly aims to remove surface wear and cracks, and to recover
the running part of the thread. Presuming linear deterioration, wear rate can be
estimated as follows:

SWR(n) = 105 × (DO0 − DOn)/S (2.5)

where the SWR(n) is the service wear rate, expressed in mm /105 km, the DO0
is initial diameter of the wheel, DOn is the diameter after n-th reprofiling of the
wheel, S is the running distance of the wheel until n-th reprofiling [23]. Maintenance
engineers can plan schedule to exchange wheels based on SWR(n).

16



3
Maintenance actions

There are two major tasks in railway maintenance: inspection and maintenance
work itself. Inspection task includes monitoring the conditions of railway systems
and detecting faults. On the other hand, maintenance work implies series of actions
to fix failures in railway systems.

Under the interviews with the companies it was clear that different components
have different maintenance plans. Much of the maintenance work is determined by
planning intervals from historical data to decide the cycles. Other components are
handles using a conditioned based maintenance decided from measurements.

3.1 Track system
Trafikverket in Sweden is today in charge of maintaining 14 200 km of railway [24].
The main focus is to make sure that the railway system is safe and available for
traffic. In the maintenance plan from Trafikverket [24], it is described that the two
main maintenance activities categories carried out are:

Base maintenance
In this category, both supportive maintenance and preventive maintenance are in-
cluded. It can overall be concluded that the base maintenance aims to keep the
railway functioning, without making it better or worse. The supportive maintenance
includes matters such as emergencies and unpredictable accidents. This could be
for example the signalling system out of order, an animal getting hit by the train or
problems related to snow during the winter.

The preventive maintenance is divided into condition based and predetermined
maintenance as shown in Figure 3.1. The condition based maintenance is deter-
mined thorough inspections and controls, and money assigned to this part is deter-
mined thorough historical experiences. The predetermined maintenance is carried
out periodically and is planned early in advance.

Reinvestments
Along with basic maintenance, reinvestments is the other major part of the mainte-
nance carried out. This category aims to keep the function quality of the railway in
a long term view by replacing parts that are about to pass their expected lifetime.

17



3. Maintenance actions

Trafikverket describes that their goal is to increase the proportion of reinvestments
compared to base maintenance, since this will be more cost efficient [24].

Figure 3.1: Maintenance categories. Figure by the authors.

3.1.1 Detecting faults
It is of importance to be aware of the condition of the track, which is why different
methods are used to collect data. This data can then be used to perform condition
based maintenance on the track system. To detect geometric faults on the rails, of-
ten caused by wear and settlement in the ballast, a measuring vehicle could be used
as shown in Figure 3.2. This measures the vertical and lateral deviation for each rail
[11]. The distance between the two rails is also measured, both in the lateral and
vertical direction. This is then analysed to decide if corrective maintenance should
be carried out.

Figure 3.2: Measurement train to monitor track. Figure from [25].

18



3. Maintenance actions

Cracks and other types of damage are often caused by fatigue on the rail such faults
can be discovered through ultrasonic inspections or eddy current techniques which
are performed by of a measuring vehicle [14]. The rail head profile which can be
damaged due to plastic deformation or wear can also be inspected by a vehicle or
a measuring trolley. Another example of more monitoring to allow condition based
maintenance is the time measurement of a switch to change position. If it repeatedly
is taking too long, this will be alarmed and the switch will be lubricated by a worker.

3.1.2 Maintenance measures

Many forms of corrective maintenance are carried out on the railway. Some are
simple, like adding lubrication to a switch, while some require large machines per-
forming the work. Track geometry faults can be fixed by improving the condition of
the ballast. This is done by a tamping machine in Figure 3.3, which with the help
of force and vibrations push the ballast into the desired position. This restore the
track geometry.

Figure 3.3: Tamper and ballast regulator. Figure from [26].

To fix cracks in the rail caused by fatigue, either welding or replacement of the rail
can be the solution. When the rail is replaced, usually at least 5 m of the rail is
removed and the new rail is welded to the old. Of course, welding is always crucial
since it can give rise to problems like thermal cracks related to high tensile residual
stresses [16]. A measure used to correct the rail head profile is grinding as shown in
Figure 3.4. This is typically done by a grinding train.

19



3. Maintenance actions

Figure 3.4: Rail grinder. Figure from [27].

Another method which helps to decrease the deterioration of the railway track and
wheels is to decrease the friction forces. This can be done by lubrication, and is
used in narrow curves. Lubrication is added by a device which senses when a train
is coming from vibrations. Too much lubrication should not be used, since this can
cause braking and traction problems [11].

3.1.3 Challenges

Trafikverket describes in their maintenance plan [24] that an increase in traffic will
affect the cost of the maintenance being done. This is due to:

• Increasing traffic decreases the time of coherent maintenance, which creates
costs for when the machines and work is standing still.

• Short time slots for maintenance leads to provisional solutions, while waiting
for larger operations.

• The total need of maintenance is increased which leads to higher costs of
machines and staff.

• Maintenance during day time may cause traffic disturbances, and higher work-
ing costs on nights.

3.2 Rail vehicles

As many other types of vehicles, preventive maintenance is carried out on rail vehi-
cles. This is often predetermined maintenance which is planed by specifying what
should be done and how often. In the interview with LKAB [9], it was explained
that large maintenance works are planned regularly and the cycles are based on
historical experience. Condition based maintenance is also performed on the vehi-
cles, this often consist of smaller jobs that need to be done. An example of this is
reprofiling of the wheels, which is done about three to five times during the life of
one wheel in LKABs case.

20



3. Maintenance actions

3.2.1 Detecting faults

It is possible to detect faults such as wear, fatigue, cracks and out-of-roundness on
the rail vehicles to prevent accidents. This is done with the help of both track and
workshop based detection to avoid serious accidents like derailment which can have
devastating outcomes.

3.2.1.1 Track based detection

It is possible to some extent to monitor the condition of the wheel, axle and the
bearing box on the vehicle, which all are critical components which can lead to a
derailment if they were to break. Common methods to detect some types of dete-
rioration mechanisms of these components are heat and noise sensors [10]. If there
is problem with bearing deterioration this will result overheating, which will be
alarmed with the heat sensor. The noise sensor will alarm if any irregularities are
detected, like a damaged bearing.

An other way of monitoring wheel out-of-round conditions is to detect wheel–rail
contact force on the track as shown in Figure 3.5. The wheel impact load detector
can measure dynamic loads for example via rail mounted strain-gauges. The detec-
tor can derive quantified impact effects from measurements, which represents wheel
out-of-roundness levels. [28]

Figure 3.5: Wheel impact load detector at Sunderbyn. Figure by Matthias
Asplund, Trafikverket, from [29].

3.2.1.2 Workshop based detection

The maintenance work for detecting faults is also carried out on the workshop.
There may be multiple sensors installed in a wheelset diagnostics system as shown
in Figure 3.6. These sensors analyze wheelset conditions such as out-of-roundness,
wheel diameter, wheel profile, and wheel tread wear.

21



3. Maintenance actions

Figure 3.6: The wheelset diagnostics system ARGUS. From [23].

To detect axle deterioration in the form of fatigue, ultrasonic testing can be done
[17]. This is important since if an axle was to brake, this can lead to a derailment.
Other methods that are used is monitoring the wheels condition, both using of visual
inspections and measurements.

In the interview with LKAB [9], it was stated that they can often see wear on all com-
ponents and they therefore may to decide what components that need maintenance
or replacement. Some tests which can help with this is testing the door system,
coupling system and computerised break tests for each wagon. They thereby ensure
that the train will be able to run until the next service.

3.2.2 Maintenance measures
Different methods to maintain the components are carried out on the vehicles, and
according to LKAB, 80% of their maintenance budget is due to the wheels [9].
The method that wheels are maintained is through reprofiling. This will extend
the lifetime of the wheel and give a new solid surface. To maintain bearing boxes,
lubrication is important, since this otherwise can give rise to melting of the axle
in too high temperatures [17]. Replacement of different deteriorated components of
the vehicle is an important way of maintaining and the replacement intervals are
often decided from historical data.

3.2.3 Challenges
It is crucial to plan vehicle maintenance, since the location of where the maintenance
is performed is of importance. If something on the vehicle breaks out on the line,
it can be hard and expensive to fix as compared to in a workshop. In the interview
with Green Cargo, they expressed their concerns with not having enough workshops,
as well as the trains being to long for the intended workshop slot. This means for

22



3. Maintenance actions

example that they can only maintain one train at a time, instead of two trains which
the slot in the workshop is intended to be able to fit [8].

3.3 Effect of increasing demands on maintenance
Axle load
In rail vehicle maintenance, wheel wear and cracking will significantly grow with
higher axle load. Maintenance frequencies for wheels, bearings, and wheel axles
are expected to be higher. Maintenance engineers in the workshop need improved
inspection systems to check condition of wheel wear.

Operation frequency
Typical relationship between load magnitude and deterioration is exponential as
mentioned in Chapter 2. When operating frequency of trains becomes double, de-
terioration of rail vehicles also doubles.

Speed
With faster trains, the wheel–rail contact loads will have a larger scatter in mag-
nitudes leading to wheel and rail damage. Faster trains are also more sensitive
to different defects resulting in higher requirements of maintenance [4]. Figure 3.7
shows that faster trains generate more high magnitude load events, which accelerate
deterioration.

Figure 3.7: Impact load distribution regarding the influence of speed. Figure
from [30].

23



3. Maintenance actions

24



4
Decreasing needs of maintenance

4.1 Track system

4.1.1 Ballasted and slab track
Heavy axle loads and high speeds put demands on the track. To keep a high safety
and a low track deterioration, ballasted tracks need to be designed after the de-
mands with components of high performance. High performance track can for ex-
ample have continuously welded rails attached with pandrol fastenings to concrete
sleepers, while low performance track can have rail with joints attached with spike
fastenings to wooden sleepers [11]. The choice of components will affect how well
the track meets the demands from the traffic. If the track is subjected to higher
demands than what it was built for, it will deteriorate too quickly and thus it will
also affect the need for maintenance.

Slab track is, compared to ballasted track, more stable and can withstand geometri-
cal irregularities better. There is also no need for ballast actions, such as completion
and cleaning, making it possible to save up to 70 percent in maintenance cost. On
the other hand, it should be mentioned that the construction of slab track is far
more expensive than for ballasted track, as well as the reparation of arisen track
damage and wanted track changes are more complicated, time-consuming and costly
[11].

4.1.2 Rails
Track of continuously welded rails gives less wheel and rail wear, since they provide
a more gentle transition, and do not need as much inspection and maintenance as
track that is not continuously welded [11].

To reduce gauge corner wear, premium grade rails with higher tensile strength can
be used [11].

4.1.3 Managing friction forces
Lubrication can be used to reduce the friction forces, and hence to reduce wheel and
rail damage, with the constraint not to give the train problems with traction and
braking [11].

25



4. Decreasing needs of maintenance

4.2 Rail vehicles
If the upgrade of capacity is done without changing the fleet of wagons, the wagons
will have a faster degradation since they will have more loading per time unit [4].

4.2.1 Tare mass
The weight of the wagon is related to the maintenance [11]. With less tare mass,
the payload can be increased without the need of increasing the axle load. For
example, aluminium has a lower density than steel, but unfortunately it has a lower
fatigue strength. To overcome this kind of characteristics, maybe some type of
sandwich structures or composites, if they get economically competitive and capable
to withstand higher loads, can be possible in the future [10].

4.2.2 Rigid-frame and bogie wagons
Wagons with bogies can cope with more payload, since it will be distributed on
four axles instead of two axles, without exceeding the maximum permitted axle
load. Bogie wagons can also be longer than rigid-frame wagons since their axles
can rotate more vertically. However, weight is added with bogies. In addition,
complexity is increased, making the wagons with single axles better weight-wise,
cheaper and easier to maintain [10]. A rigid-frame and a bogie wagon can be seen
in Figure 4.1.

Figure 4.1: Rigid-frame and bogie wagons. Figure by the authors.

4.2.3 Angle of attack
The creepages and creep forces, related to wear and rolling contact fatigue, can be
high due to a large angle of attack that occurs when the train travels through a
curve. The angle of attack can be reduced with an increased curve radius, a less
stiff wheelset suspension and a shorter wheelbase. For bogies with radial steering,
flange wear can decrease but tread wear can increase leading to hollow worn wheels
[11].

26



4. Decreasing needs of maintenance

4.2.4 Tread and disc brakes
Brake blocks, that act on the running tread, are common on freight wagons due to
their low weight and simpleness. To avoid roughening of the wheel tread, and the
risk of thermal overload of the wheels, disc brakes can be used. Disc brakes consists
of brake pads that act on separate discs on the axle or the wheel. The performance
of the disc brakes is usually better than tread brakes [11] since the friction is less
speed dependent. But on the other hand, tread brakes clean the running surface and
small roughening can improve the adhesion. The disc brakes are also more costly,
heavier and harder to maintain. But they are also less noisy and the brake pads
have a relatively long life-time before they need to be changed [10].

4.2.5 Material of brakes
The material of the brake blocks is also affecting the wear. For example, with cast
iron blocks there will be more wear on the blocks, since the steel of the wheel is
harder. With composite materials and sintered blocks, which have low block wear,
there will be more wheel wear. It should also be mentioned that composite materials
blocks increase the risk of thermal overload in the wheels and that sintered blocks
are expensive. These two alternatives are also better when it comes to cleaning of
the wheel tread as well as they are less noisy and less friction dependent than cast
iron blocks [10].

4.2.6 Managing locked wheels
Anti-slip devices can make the wheels rotate during braking and thus prevent them
from getting locked which can lead to wheel flats [10].

4.3 Avoiding complexity
If wagons and track are simple, there are less things that can break and less to
maintain. The need of maintenance can be decreased if there are few parts that
are to be handled. For example, the handling by the customer is very small for
tank wagons since they only connect a hose to the wagon. The tank wagon does
not have any doors or similar things that can break, meaning that the maintenance
can be focused on wheels and brakes of the tank wagons [8]. On the track reduced
complexity to avoid too many switches near train stations where many trains pass,
brake and accelerate.

See also Chapter 4.2.2 for how rigid-frame and bogie wagons affect the complexity,
Chapter 4.2.4 for how tread and disc brakes affect the complexity, and Chapter
5.2.3.2 for how sensors affect the complexity.

27



4. Decreasing needs of maintenance

28



5
More efficient maintenance

5.1 Maintenance strategies for increasing demands

5.1.1 Stricter maintenance intervention

Maintenance actions for high track quality can not only extend track lifetime but
also be economically sustainable in the long term. For instance, tamping work with
a stricter intervention level increases maintenance frequency in short term. How-
ever, higher track quality results in reduced a need for tamping and expands the
lifetime of the track in the long term [31]. This can also be applied to rail vehicle
maintenance.

In other words, it is necessary to reinforce short-term maintenance such as moni-
toring wear, damage, and fatigue. More frequent short-term maintenance can save
costs and extend the life-time of wagons, resulting in reduced needs for major main-
tenance.

5.1.2 Field maintenance outside workshop

Based on the interview with Green Cargo, main issues of increasing maintenance
demands relates with maintainability of workshops [8]. If current maintainability
remains same without improvements, it can lead making workshops crowded.

One of solutions to this problems could be maintenance work for wagons outside
the workshop. Those wagon maintenance works are under operation named ’R0’
to prevent larger deterioration [8]. Wagon maintenance work outside of workshop
can consist of detecting faults and wear in wheel sets. Those preliminary checkups
become fundamental information to maintenance decision in workshops.

This solution requires portable detecting devices/sensors which maintenance engi-
neers can install outside workshops. Therefore, it will primarily need technological
support to realize the solution.

29



5. More efficient maintenance

5.2 Automation and digitalisation

5.2.1 Digital twin
The resources and activities that are needed to maintain the railway infrastructure
can be more effectively utilised, optimised and developed with the help of digital
twins [32].

5.2.1.1 Simulation

With a digital twin, and the data from information systems, it is possible to sim-
ulate and study for example maintenance operations and changes. It can then be
seen if the operations and changes are suitable and how they should be handled
before making them on the physical system. This makes it possible to improve the
performance of maintenance, as well as the impacts on the trains can be examined
and better prepared for. Thus, a digital twin can save both money and time [32]
since simulations make it possible to see the effects faster and in advance, which
enables an optimisation of the intended activities.

It can also be desirable to simulate the effects on availability of a vehicle if a main-
tenance parameter is changed. For example, it may be possible to simulate the
effects on the number of reprofilings each year, the needed size of the wheel pool
and the need of machines if the maximum allowed flange height is decreased by one
millimetre.

5.2.1.2 Prediction

Unreliable elements and the planning of maintenance can be identified with the
help of constantly updated diagnostics [32]. The railway can be carefully examined
and the condition of the operating elements can be predicted in real time with a
digital twin. This makes it possible to predict the need for maintenance work. Also,
potential problems can be caught before they impact traffic [33].

5.2.1.3 Safety and efficiency

With the possibility to monitor the track remotely, less manual track inspection will
be needed, at the same time as the work is done in a more controlled environment,
which increases the safety for staff. It also improves maintenance efficiency [33]. For
example less travel time is needed for maintenance staff to do inspections.

5.2.2 Maintenance planning
The scheduling of maintenance can be improved with automation and digitalisation.
Scheduled maintenance is generally safe and the standard practice today. The sched-
uled maintenance can be done according to the safest maintenance periods based on

30



5. More efficient maintenance

historical performance and estimations from manufacturers, making it imprecise [34].

With scheduled maintenance, a lot of unnecessary maintenance is done since it
is generally based on cases close to the worst, meaning that some parts will be
changed earlier than required. However, early failure of components may arise due
to manufacturing faults, assembly mistakes or reparation mistakes. In the worst case
these are not caught because they are happening between the scheduled maintenance
[34].

5.2.2.1 Condition based maintenance

Condition based maintenance can be scheduled and made according to data from
sensors that give an understanding of the actual condition of the track or rolling
stock. This makes it more precise than ordinary scheduled maintenance. With con-
dition based maintenance, less unnecessary or too early maintenance is done which
overall lowers the amount of needed maintenance. Additionally there is a larger
probability that early failures due to manufacturing faults, and so on, will be de-
tected and caught in time [34].

Condition based maintenance with too low or too strict limits before maintenance
is triggered must be avoided. Some kind of foresight and possibility to plan mainte-
nance before worst case failures occur is needed to keep a constant and manageable
flow in the workshops. It is not good if the workshops are overfull one day and
empty the next day.

5.2.2.2 Predictive maintenance

Physical modelling, artificial intelligence and machine learning programs can work
on the collected data from sensors, by comparing them with a limit state, to be able
to predict when maintenance is likely to be required. With predictive maintenance,
the maintenance resources of operators can be better scheduled in advance and
allocated. This improves the management of the resources and reduces the down
times [34].

5.2.3 Drawbacks
5.2.3.1 Vulnerability

With an increased automation and digitalisation, the risk of cyber attacks is also
increased and it becomes more important with cyber security [35].

5.2.3.2 Complexity

A freight wagon is a fairly simple mechanism [8]. The complexity of the wagon
will increase if it gets equipped with sensors to collect data, at the same time as
sensors need power to operate. It can also be too much complexity if every wagon
in the fleet is equipped with the measuring system. This will also introduce more
components on the wagon that can fail or break down [9]. It may therefore be more

31



5. More efficient maintenance

suitable to measure the condition of the wagons from the track, instead of from the
wagons. One sensor from the track can thus measure the condition of all the passing
wagons, as well as there perhaps may be less sensors to take care of.

5.2.3.3 Amount and quality of data

A lot of data can be collected with sensors, but it also needs to be quality ensured,
evaluated and stored somewhere. Sometimes quality is better than quantity, and
for the data to be valuable and useful, it needs to be trustable with few uncertainties.

For example, the measuring tools may have to be calibrated to present the correct
values. Further, trains during braking, accelerating and curving probably give dif-
ferent values than trains with constant speed at straight track.

It may be possible to get a confirmation that there is something wrong with a wagon
if the sensors at the track that measure the condition of the wagons are located rather
close to each other and signals for the same problem. With too few sensors at the
track or with sensors in the wagons, it may be more unclear if it is something wrong
with the sensors or with the actual wagon.

5.3 Simplify for maintenance
If the track and the rolling stock are simple to maintain, it can lead to that they also
become faster, cheaper and safer to do maintenance on. The availability of track
and rolling stock will be higher if the maintenance can be done faster.

See also Chapter 4.2.2 for how rigid-frame and bogie wagons affect the simplicity
of maintenance, Chapter 4.2.4 for how tread and disc brakes affect the simplicity
of maintenance, Chapter 4.3 for how avoiding complexity affects the simplicity of
maintenance and Chapter 5.2.3.2 for how sensors affect the the simplicity of main-
tenance.

5.3.1 Design for maintenance
A wagon, for example, can become easy, cheap and fast to maintain if the maintain-
ability has a high priority during the development. It can result in that a bogie can
be taken apart and put together within ten minutes by an experienced worker [9].

5.3.2 Modularisation
To make the maintenance more effective, a wagon or a switch, for instance, can
be divided into modules that can be swapped against identical modules if needed.
Every subsystem can have its own deterioration limit. For a wagon, it can then for
example be possible to change the door system, the coupler system, the wheels or
parts in the bogies at once [9]. For a switch, it can for example be the switch blades
or the crossing nose.

32



5. More efficient maintenance

5.3.3 Standardisation
Standardisation can perhaps make it possible to have the same type of parts or
modules in for example different kind of switches or different type of wagons. This
can lead to that less unique parts or modules have to be stocked in the workshops.

5.4 Track system

5.4.1 High speed measuring
There are rail maintenance machines that can measure the condition of the track
during normal scheduled operations, without having to close down the track. Dif-
ferent maintenance scenarios, including costs, can then be determined from the
interpreted data of the measurements that have been taken [36].

5.4.2 Measuring with locomotives
To not make the measuring machines take up time slots in the track, the locomo-
tives of the trains can be fitted with measuring instruments for those measurements
that can be done at normal speeds during normal train operations. This can make
the track more available either for train operations, with for example freight, or
for maintenance work to be done. Also, measurements can be gathered more fre-
quently which may lead to an increased understanding and an easier planning of the
maintenance of the track.

5.4.3 High speed grinding
Rail grinding can be done in the form of high speed grinding with machines that
operate at speeds up to 80 km/h. This means that it can be scheduled to any slot in
the timetable without much need for track preparations or closures. Beside removing
small and medium rail defects, the high speed grinding machines also prevent the
growth of new defects which extends the service life of the rail with up to 100% [36].

5.5 Rail vehicles

5.5.1 Change in maintenance plans
The maintenance can be optimised by changing maintenance plan if parts that still
have a long lifetime left are encountered. This can be good both for the maintainer
and the customer of the train since the maintainer does not have to change the part
and customer does not have to pay for it [37].

5.5.2 Collect maintenance needs
The service of the wagons can be maximised if the components of the wagon that
have roughly the same degradation are collected and changed at the same time,

33



5. More efficient maintenance

instead of taking the wagon to the workshop every now and then to change a com-
ponent [9]

5.5.3 Increase preventive maintenance
One way to make the maintenance more efficient can be to increase the mainte-
nance tasks of preventive maintenance and thereby making the trains come to the
workshops less frequently [37]. This can increase the availability of the trains since
they will have more consequent time in traffic before they return to the workshops
again.

34



6
Conclusions and future

recommendations

Many interesting inputs from the industry have been received during the interviews
in this project. Comparing the differences between them can give an even better
idea about the challenges with freight trains. During the interview with LKAB, it
was clear that their main goal is to increase the axle load rather than increase the
frequency or speed of the trains. When speaking with Green Cargo, their plan of
increasing their freight demands was to increase the frequency, and not increase axle
load. These two companies operate under extremely different conditions. Whereas
LKAB have a very uniform freight and path, Green Cargo operates with different
forms of freight and many different paths in the country. What this implies, is that
there is simply not one solution that will fit all, and that needs to be considered
when approaching solutions.

During the project, the deterioration depending on the load and frequency have
been looked into. What can be concluded is that increasing the load will in theory
make the deterioration grow exponentially. Increasing the frequency of train will in
contrast show a linear increase in deterioration.

One of the key parts of efficient maintenance is to avoid carrying out maintenance
on components which does not need it. This is one of the risks with preventive main-
tenance, being that the condition of the component which is maintained or replaced
is good, even though historical data of similar cases might be different. Condition-
based maintenance is therefore preferable. What needs to be considered though, is
that measurements with sensors which have to be calibrated and maintained can
become even more expensive than having to replace or maintain the component. Of
course, the cost is not always what has to be considered either since sustainability
is a key factor. Replacing parts which do not need replacement is therefore not
preferable, even though the sensors affect on sustainably also have to be considered.

According to what has been discussed above, knowing the condition of the vehicle
and track is important to be as efficient as possible. During this project, both re-
search and interviews with professional staff have been carried out. What seems
to be an area that is interesting to develop further is combining the measuring of
track condition, with the trains that are already running instead of having special
vehicles to perform this. This will open up more slots on the track for freight and
passenger trains, while also making the detection of faults more efficient. What

35



6. Conclusions and future recommendations

also has been discovered, mainly under the interviews, is the need of being able to
predict the condition of both vehicles and the track even better. This can be done
by collecting even more data and developing evaluation and prediction tools that
later will decrease the need of manual inspections.

During the project, different approaches of increasing capacity have been considered.
Increasing the load and speed of the train are two effective ways of increasing the
freight capacity. They, however need very careful analysis and inspection since they
are likely to form a larger deterioration than having more frequent trains.

Reducing complexity of the wagons and locomotives can be an important mat-
ter when it comes to maintenance. This often makes the wagons more simple to
maintain in comparison with the locomotive, since the latter has more components
included, which creates a larger risk of something failing. As discussed in the report,
it is therefore beneficial to have sensors measuring the condition of the wagons and
locomotive track based, as a sensor on each wagon leads to a bigger complexity.

Short interval maintenance is critical in monitoring the condition of locomotives
and wagons. Stricter maintenance intervention can initially require more human
resources and facilities. However, in the long-term perspective, it is likely to have
advantages and benefits in economical and sustainable effects.

36



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DEPARTMENT OF SOME SUBJECT OR TECHNOLOGY
CHALMERS UNIVERSITY OF TECHNOLOGY
Gothenburg, Sweden
www.chalmers.se

www.chalmers.se

	Introduction
	Background
	Problem definition and research questions
	Problem definition
	Research questions

	Interviews
	Alternative ways to increase freight traffic
	Significantly higher capacity
	Upgrading of existing lines
	Some challenges beside deterioration and maintenance
	Utilisation of the upgrade
	Interplay with passenger traffic
	Longitudinal forces in the train
	Parking spaces and handling of wagons


	Limitations in research

	Deterioration
	Deterioration mechanisms
	Track system
	Rails
	Rail joints
	Switches and crossings
	Rail fastenings
	Sleepers
	Ballast
	Catenary

	Rail vehicles
	Wheels
	Axles and bearing boxes
	Brakes
	Springs and dampers
	Buffers and couplers
	Pantographs

	Modelling of deterioration
	Deterioration models
	Track system
	Rail vehicles


	Maintenance actions
	Track system
	Detecting faults
	Maintenance measures
	Challenges

	Rail vehicles
	Detecting faults
	Track based detection
	Workshop based detection

	Maintenance measures
	Challenges

	Effect of increasing demands on maintenance

	Decreasing needs of maintenance
	Track system
	Ballasted and slab track
	Rails
	Managing friction forces

	Rail vehicles
	Tare mass
	Rigid-frame and bogie wagons
	Angle of attack
	Tread and disc brakes
	Material of brakes
	Managing locked wheels

	Avoiding complexity

	More efficient maintenance
	Maintenance strategies for increasing demands
	Stricter maintenance intervention
	Field maintenance outside workshop

	Automation and digitalisation
	Digital twin
	Simulation
	Prediction
	Safety and efficiency

	Maintenance planning
	Condition based maintenance
	Predictive maintenance

	Drawbacks
	Vulnerability
	Complexity
	Amount and quality of data


	Simplify for maintenance
	Design for maintenance
	Modularisation
	Standardisation

	Track system
	High speed measuring
	Measuring with locomotives
	High speed grinding

	Rail vehicles
	Change in maintenance plans
	Collect maintenance needs
	Increase preventive maintenance


	Conclusions and future recommendations
	References