Technology

Technology

Railway Technology Today 2 (Edited by Kanji Wako)

The Mechanism of Railway Tracks
Shigeru Miura, Hideyuki Takai, Masao Uchida, and Yasuto Fukada

Railway Operation in JapanThe history of railways in Japan dates backto September 1872 when commercial
operation started over a 29-km track between Shimbashi (Tokyo) and Yokohama.
Japan has achieved a tremendous development, both social and economic, overthe following 125 years, and railways
have been no exception. The railway networks in this relatively small land total
over 27,000 km, and up to 2.2 million
people ride trains each day. The fiveshinkansen lines stretch 2200 km with
operating speeds of 260 to 300 km/h.
Shinkansen cover the 515-km stretch between the two largest cities, Tokyo andOsaka, in 2 hours and 30 minutes. The
high efficiency of railway transportation
puts railways ahead of air transport in Japan, where the dense population is scattered along the Pacific coastal plain.
The progress of railways and their role insociety is supported by new technological achievements in many areas. Safety,
speed, and ride comfort have always beenmajor concerns for Japanese railway companies. The other major concerns today

are reducing noise pollution for people
living near tracks, and preserving the natural environment. More recently, easier
maintenance has become an important
issue due to labour shortages and the needfor higher efficiency.
Track is one of the most important technical elements in railway operations. Tracktechnology has developed in parallel withthe railway itself. Current concerns of railways are also technical issue for tracks.
This article discusses the present status oftracks in Japan, and the future outlook.

Structural Analysis of Tracks
Basic structure
Japan is a mountainous archipelago withnarrow coastal plains. Consequently,
Japanese railways have many sharp
curves, tunnels, embankments, and steep
grades. The first railway in Japan was built
using a narrow gauge (1067 mm) to meetthese geographical conditions and theneed for economy; the narrow gauge became the standard for all state-owned railways until the first shinkansen in 1964.
Figure 1 shows that railway track consists

Figure 1 Basic Structure and Function of Railway Tracks
Source ofvibration

Weight of rail

RailRail fastening

Vibration blockedby fastening spring
Vibration absorbed
by rubber pad

Rubber pad

Sleeper
Weight of sleeper

Ballast (stone)(a) Structure

38

Japan Railway & Transport Review • March 1998

Vibration absorbed
by stone friction
and spring action

essentially of rails and sleepers, laid in and
fixed by ballast on a road bed. This economic design, which was chosen on thebasis of experience, has remained virtually unchanged irrespective of other subsequent technical progress. Tracks are
long, large structures stretching hundreds
or thousands of kilometers. In addition
to economy, the design is a rational structure for supporting heavy fast trains on soft
ground. It is easy to maintain and offers
outstanding vibration and noise performance. Many attempts have been madeover the past 100 years to develop otherdesigns but none have been good enoughto replace the conventional design.
As discussed later, slab track is a recent
preference for high-speed operations, requiring less maintenance. However, conventional ballasted track is still found on
more than 90% of railways in Japan.

Rails
Japan’s first line used vertically-symmetrical, wrought-iron double-headed rails.
They were soon replaced around 1880 byasymmetrical steel flat-bottom rails ofgreater toughness. These first rails weighed
29.8 kilograms per meter (kg/m) and were
7.3-m long. The weight and length werelater increased to carry more trains at faster
speeds. Today, Japanese trains run on 50or 60-kg rails. The 60-kg rails have thelargest cross-sectional area and are usedon all shinkansen tracks and other major
sections (Figure 2).
The standard rail length is 25 m, but continuous-welded rails (CWR), or long rails,
are used on main sections to improve ride
quality and reduce noise and vibration.
The CWR is subject to compression loads
due to temperature changes, which cancause buckling, or sharp lateral displacement. These phenomena are prevented
using reinforced fastenings, sleepers andballast.

(b) Function

Copyright © 1998 EJRCF. All rights reserved.

Figure 2 Typical Rail Cross Sections
40N rail

50N railCL

50T rail
32.5

32.5

32.5

46

49

32

60kg rail

CL(Unit: mm)

49

5

1 : 2.7

61

1: 2
.75

Continous-welded rails are being promoted in Japan to cut noise, vibration, andmaintenance costs. Rails can be welded
end-to-end using any of four processes:
flash butt, thermit, gas pressure, and enclosed arc. Japan is unique in using thegas pressure process and the enclosed arc
in addition to the other two, commonlyused in other countries.
In 1996, the JR group completed about
79,000 welds; 40% were by thermit welding, 26% by gas pressure, 25% by flash
butt, and 9% by enclosed arc. The gaspressure process is less efficient than the
flash butt process, but it is widely used
for both factory and track-side welding

Gas pressure track-side welding

Copyright © 1998 EJRCF. All rights reserved.

174

8.25

1:10

63.5

Welding

94.9

160

87.5

153

8

1 :4

1 :4

68

30.1

1:9

26.5

7

74

7.5

73.5

140

5

25.5

1 :4
1 :4

.75
1: 2

30

41

1 : 2.7

72.5

because the equipment is easily portable
and the joint quality is as good as that of
the flash butt process.

Sleepers
The sleepers binding the rails were usually made of hardwood timber. Concrete
sleepers, introduced in early 1950s, areused on most trunk lines today becauseof their longer service life and greater trackstability. Although timber sleepers havegood elasticity and are lighter and easier
to handle than concrete sleepers, theirmain drawback is short service life due todeterioration. Synthetic sleepers made of
hard polyurethane foam and glass fiber
are a recent unique development in Ja-(RTRI)

pan. They are designed for long service
life (more than 60 years) while maintaining the physical properties of wood sleepers. They are being used increasingly oversteel girder bridges, switches, and othersections where maintenance or replacement is difficult.
‘Ladder sleepers’ are another on-goingdevelopment. They consist of 12-m long
pre-stressed longitudinal concrete members bound by lateral steel tubes like aladder. The rails are supported continuously on the concrete members, which
distribute the load lengthwise, reducing
the need for ballast maintenance.

Rail fastenings
In the early days, dog spikes or othersimple devices were used to fasten the rail
to timber sleepers. With the introductionof concrete sleepers, the spikes were replaced by double elastic fastenings inwhich the rail is fastened by a spring using rubber pads or other cushioning materials inserted between the rail andsleeper. Rail fastenings distribute load anddampen vibration and are an essential
component in high-speed train operation.
Leaf springs are used in Japan primarily
because of cost and adjustability, and inFrance because of fastening force andbearing ability. Wire springs are preferredin Germany because of fastening force

Newly-developed ‘Ladder Sleepers’(RTRI)

Japan Railway & Transport Review • March 1998

39

Technology

and adjustability (Figure 3).
Figure 3 Different Rail Fastenings

Shinkansen track structure

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Japan Railway & Transport Review • March 1998

Shinkansen 102 Leaf Spring

TGV Nabla Leaf Spring

ICE Vossloh Wire Spring(RTRI)

Figure 4 Proportions of Ballasted and Slab Tracks on Shinkansen
600
516(100%)

Ballasted track
Slab track
453
(90%)

Track distance (km)The Tokaido Shinkansen began operationin 1964 between Tokyo and Osaka at a
maximum speed in excess of 200 km/h
for the first time in the world. When theline was first envisaged, there were twoplans for the gauge. One was to increase
the transport capacity by adding narrowgauge double track to the existing TokaidoLine. The other was to increase the capacity while halving the journey time bybuilding a standard-gauge double-trackline. The latter plan was eventually chosen, and the new line took a different routefrom the old Tokaido Line with many viaducts, embankments, and tunnels andwithout level crossings.
New rails, sleepers, and fastenings were
designed for the high-speed line. The
Tokaido Shinkansen track features:• 1435-mm standard gauge• CWR and concrete sleepers throughout• Movable nodes eliminating gaps at turnouts and crossings• Long rails joined by expansion joints
to minimize gauge fluctuation due tothermal elongation and shrinkage• New-design 53 kg/m rail (50T and later
entirely replaced by 60 kg/m rail)
The Tokaido Shinkansen was soon followed by the Sanyo, Tohoku, Joetsu andHokuriku Shinkansen built from 1972 to
1997. The maximum speed was raised
from the initial 210 km/h to a more recent 260 to 300 km/h. Around 1967, efforts were started to develop slab tracks
to prepare for the expected sharp increasein transport demand and higher operation
speeds. Slab track was first introducedon the Shin-Osaka to Okayama sectionof the Sanyo Shinkansen which started
operation in 1972. Today, it is the standard track bed for shinkansen. Figure 4
shows the proportions of ballasted andslab tracks used on each shinkansen.

400

273
(69%)

200

0

156
(95%)

0
(0%)
TokaidoTokyo –
Shin-Osaka

255
(95%)

125
(31%)

15
(5%)

8
(5%)
Sanyo
Shin-Osaka –Okayama105(84%)

Okayama –Hakata

48
(10%)

20
(16%)

JoetsuTohokuHokuriku

Omiya – Niigata

Tokyo –
MoriokaTakasaki –NaganoCopyright © 1998 EJRCF. All rights reserved.

Slab Tracks
Slab versus ballasted tracks
About 30 years ago, European railway
engineers in countries with advanced railway technology were examining car andtrack systems for trains running at speeds
over 200 km/h. Their main concern waswhether it would be possible to repair the
track ballast frequently enough before it
was loosened by the severe impact of thehigh-speed train operation. At that time,
Japan decided to use ballasted tracks
based on the then new theory of ‘optimization of ballasted track considering maintenance requirements’—a wise decision
later borne out by the success of theTokaido Shinkansen. The French andGerman railway operators had slightly
different views about this issue. In France,
it was thought that speeds over 200 km/h
were possible on ballasted tracks, but in
Germany, it was thought that althoughballasted track could endure speeds up
to 200 km/h, slab track or other types ofballasted tracks would be required forhigher speeds.
In May 1988, the German ICE marked aspeed of 407 km/h and then in May 1990,
the French TGV marked a record of 515
km/h—both records were on ballasted
tracks. Meanwhile, in Japan, the highest
speed at that time of 425 km/h wasreached in December 1993 on slab tracksof the Joetsu Shinkansen. The current
speed record in Japan is 443 km/h established on ballasted track on the Tokaido
Shinkansen by the experimental 300X
shinkansen belonging to JR Central.

first time on the section between ShinOsaka and Okayama on the Sanyo
Shinkansen. Today, slab track is the standard on concrete bed sections such as
viaducts and tunnels. Slab tracks are also
being used experimentally on theearthwork section between Takasaki andNagano of the Hokuriku Shinkansen (presently called Nagano-bound Shinkansen)
which began operation in October 1997.

cases. The same holds true for tunnel sections because the lower track height reduces the tunnel cross-sectional area,
cutting construction costs by about 30%.
This alone is more than likely to offset thedifference in construction costs between
slab-track and ballasted-track railways. As
a result, some people claim that slab track
is more advantageous.

New Track Designs

Economy of slab tracks
A 1990 comparison of the economic merits of ballasted and slab tracks on the
Tohoku Shinkansen shows that slab track
construction costs 1.3 times more thanballasted tracks. However, this difference
balances out after about 9 years due thelower maintenance costs of slab track.
Since slab track is lighter than ballasted
track as a whole, the construction cost of a
new railway based on slab track, including the viaduct cost, can be less in certain

Labor-saving track designs
for existing lines
It is generally thought that the following
measures minimize normal track subsidence:• Increasing track rigidity or using larger
sleepers• Increasing track elasticity• Increasing binding of bed
The photograph on the next page shows

Figure 5 Structure of Slab Tracka) Near slab centre

Slab
Cement asphalt
Concrete structureb) Near slab end

StopperSlabCement asphalt
Concrete structurec) Near stopper
Stopper

Structure of slab tracks
A slab track means a reinforced concrete(RC) slab laid on a viaduct or other rugged bed, and secured to the bed using
cement asphalt (Figure 5). Developmentof slab tracks began in 1965 and, after
many experimental installations, they
were used in commercial operation for the

Copyright © 1998 EJRCF. All rights reserved.

Japan Railway & Transport Review • March 1998

41

Technology

Track Maintenance
Need for track irregularity
controlLabour-saving E-type paved track

the E-type paved track, an example of alabour-saving track that has been developed and is now in use.

(RTRI)

resilient sleepers. In addition to having
anti-vibration performance, the sleepers
can be replaced easily when elastic fatigue occurs.

Vibration-reducing tracks
A growing social concern is protecting the
track-side environment and residents from
pollution problems caused by faster train
operations or construction of projected
shinkansen. Protection from vibration andnoise is particularly indispensable. Increasing operation density and other elements are causing growing problems,
making it more difficult than ever to maintain normal conditions. Easing the needfor maintenance work is also a necessity.
The photograph below shows the newlydeveloped solid-bed track with removable

High-speed turnouts
Earlier shinkansen used 1:18 turnouts
because the operation modes did not require high-speed turnouts. However, the
new Hokuriku Shinkansen uses a newlydeveloped 1:38 turnout because the newline branches off the Joetsu Shinkansen at
about 3.3 km from Takasaki Station. Thisnew turnout has a lead curve radius of4200 m, an overall length of approximately 135 m, and a high turnout side
speed of 160 km/h.

Newly-developed solid-bed track with removable resilient sleepers

42Japan Railway & Transport Review • March 1998

(RTRI)

High-speed turnout (1:38)

The frequent passage of trains on tracks,
especially ballasted tracks, loosens anddeforms the ballast and/or the bed supporting it. This leads to minor irregularities and bending (collectively referred toas track irregularity). In addition, frequent
train passages increase the grade sag atrail joints and welded joints as well as therail surface roughness.
When a carriage runs on a track with theseirregularities, it moves up and down aswell as to right and left. The behaviour
varies with the nature of the irregularity.
A carriage is typically comprised of threeelements: body, truck, and axles (Figure6). Each element has a unique natural
frequency affecting movement. A slow
change in track irregularity over a longspan (known as a long-wave track irregularity) mainly affects the vertical and lateral body vibration resulting in a poor ride.
A short-wave track irregularity (rail surface irregularity, etc.) causes shock andhigh-frequency vibration between thewheel and rail, resulting in increased loadon the track, noise, and vibration.
A carriage running along a curve at highspeed is not affected only by track irregu-(RTRI)

Copyright © 1998 EJRCF. All rights reserved.

Figure 6 Wavelength of Track Irregularity and Car Movement
larity. The passengers feel thrown towards
the outside of the curve due to the unbalanced centrifugal force which depends on
the speed. In addition, a large reaction
force is applied to the rail, causing thetruck to rotate along the curve. These factors increase the burden of track maintenance. A large, lateral track irregularity
can even cause derailment due to climbing or jumping of the wheel over the rail.
An increased lateral thrust can spread therails, also leading to derailment.
Targets for controlling track and rail surface irregularity must be established, andthe track must be inspected accordingly
at regular intervals, to maintain safety andride quality, and to minimize dynamic
loads, noise and vibration.

Long-wave trackirregularity tends tocause body vibration
Amplitude

Riding comfort

Wavelength

Vibration model of railway car
Body

Short-wave trackirregularity tends tocause wheel vibration

Truck
Wheel
and
axle
Amplitude

Axle weightfluctuation,and vibration

Wavelength

Figure 7 Design of Track Inspection Cars

Role of track inspection cars
Control of track irregularity is performedat regular intervals and consists of: (1) inspecting track condition, (2) assessing repair need, (3) planning repair, (4)repairing, and (5) confirming repair work.
The track inspection car plays an important role in inspecting the track condition,
pinpointing sections requiring repair, andconfirming the repair work.
Track inspection cars such as the narrowgauge model built in the 1960s and theshinkansen model nicknamed ‘Doctor Yellow’ (JRTR 11, front page) built in the
1970s, simultaneously measure the track
surface at three points at 5-m intervals.
Track irregularity is detected based on therelative positions of the measured points.
This method (called the ’10-m chord alignment method’) requires a special car withthree trucks. In addition, the design limits
the maximum speed to around 200 km/h.
These limitations called for developmentof new track inspection cars allowing
higher maximum speeds (for shinkansen
tracks), lower costs, and multiple functions(for conventional tracks).
These needs are currently being met bydeveloping a two-truck track inspection
car for shinkansen tracks with a maximum

Copyright © 1998 EJRCF. All rights reserved.

5000
2500

5000
2500
17500

2500

(a) Current Three-truck Car
Laser gyro unit
Digital operator

Laser reference unit (under floor)
Optical rail displacement sensor
25000(b) Planned Two-truck Car

speed in the range of 300 km/h, approaching that of commercial trains. The newinspection car uses three of its four axles
to obtain data that are converted to similar data to those obtained by the earlier
three-truck car. It also features laser-based
equipment, a lightweight optical sensor

for measuring rail displacement, a highperformance gyroscope, and other technologies (Figure 7).
Similar developments are also under way
for an entirely new low-cost track inspection car for narrow-gauge tracks. This new
system computes displacement from eas-

Japan Railway & Transport Review • March 1998

43

Technology

ily-measured acceleration; it also featuresother non-contact equipment, such as
optical and electromagnetic displacement
sensors.

Track irregularity control indexes
Ride quality is noticeably affected by longwave track irregularity; passenger cars on
both shinkansen and conventional lines
tend to sway at a frequency of 1.0 to 1.5
Hz. The track irregularity wavelength inducing this sway frequency corresponds
to 60–80 m at about 300 km/h on
the shinkansen, or 30–50 m at about 160
km/h on conventional lines (Figure 8).
However, the current 10-m chord alignment method is designed primarily for inspecting 10- to 20-m track irregularity, notfor longer irregularities. Consequently, theJRs generally use a 40-m chord alignment
method for shinkansen and a 20-m chordalignment method for conventional lines.
These methods have a better correlation
with carriage behaviour, contributing toeasier data processing and easy-to-identify control indexes.
The car’s lateral behaviour or ride quality
on curves is affected by two factors: theunbalanced centrifugal force which depends on the cant and the train speed, andthe lateral motion due to track irregularity. Ride quality evaluation taking thesefactors into consideration is used to determine the alignment maintenance target for curves.
Climbing derailment is caused primarily

Figure 8 Waveforms of Track Irregularity and Shinkansen Car Behaviour
Low correlation between track irregularity and vibration

10-m chord alignment
10 mm

40-m chord alignment

Vibration is emphasized
10 mmActual track irregularity on ground

Restored alignment
10 mm

Lateral acceleration

Irregularity causing motion
0.20 g

100 m

40 m
40-m chord
10-m chordby alignment irregularity and twist. The
former increases transverse pressure,while the latter lifts wheels due to relative twist between the truck and the track.
Until the 1970s, multiple-cause freight car
derailments were quite common. They
were found to be due to level irregularities inducing car rolling, and alignment
irregularity causing increased lateral thrust
and attack angle. Based on these findings, compound track irregularity was set
as a new control index. Freight car derailments due to multiple causes decreased significantly with improved
carriage performance and stricter inspection based on the new control index.
Shinkansen wheel-rail noise during highspeed operation primarily refers to rolling noise, occurring when sound isemitted as a result of vibration of thewheel and the rail due to minor irregularities between them. Therefore, rollingnoise can be reduced effectively by grinding out rail surface irregularities. Rail surface irregularity is evaluated by a railroughness index based on a 20-cm chordalignment. An index of 20–50 µm is thetarget for sufficiently reducing rollingnoise.
Irregularities due to rail welds and waving wear of the rail cause rolling noise,increased vertical vibration of the wheel,
and track deterioration. These irregularities must be located and corrected by rail
grinding. Rail surface roughness can beinspected directly but is inefficient due tothe slow measurement speed. As a result, a new inspection method has beendeveloped using axlebox vertical vibration acceleration, which has a close correlation with fluctuation in the load on
wheels of passenger cars. This method
more efficiently identifies trouble spots
causing such fluctuations.

10 m

44

Japan Railway & Transport Review • March 1998

Copyright © 1998 EJRCF. All rights reserved.

Use of track irregularity data
Track irregularity data obtained by a trackinspection car can be converted into digital data, combined with track environment
data and stored in a database. A track
maintenance database system called ‘micro-LABOCS’ (Figure 9) is commonly used
to store these data. It calculates track section evaluation indexes and long-wave
track irregularity, analyses the track irregularity wavelength and relationship withcar behaviour, and identifies long-termchanges in track irregularity.
The system provides a restored waveform
calculated from 10-m chord alignment
data that accurately represents the actual
track profile over a limited waveband (forexample, 6–100 m). This is comparedwith the track design profile and track
maintenance is performed to restore thedesign track alignment. Efforts are currently under way to coordinate this system with an automatic control system fortamping machines to introduce a completely new dimension in fully-automatedtrack maintenance.
■

Figure 9 ‘micro-LABOCS’ Track Maintenance Database System

Trackinspection
car

Kanji Wako
Mr Kanji Wako is Director in Charge of Research and Development at RTRI. He joined JNR in 1961 after graduating in engineering from Tohoku University. He is the supervising editor for thisnew series on Railway Technology Today.

Shigeru Miura

Hideyuki Takai

Mr Shigeru Miura joined JNR in 1969 after obtaining a Master’s de-

Mr Hideyuki Takai joined JNR in 1978 after obtaining a Bachelor’s

gree in Civil Engineering from the University of Tokyo. He is thedegree in Civil Engineering from the Tokyo Institute of Technology.

General Manager of the Track Technology Development Division at

He is a Manager in the Track Technology Development Division at

the Railway Technical Research Institute (RTRI) where he is a lead-the RTRI in charge of track structure and components.

ing engineer specializing in track dynamics and structure.

Masao Uchida

Yasuto Fukada

Mr Masao Uchida joined JNR in 1974 after obtaining a Bachelor’s

Mr Yasuto Fukada joined the RTRI in 1996 after working at Sumitomo

degree in Civil Engineering from Osaka University. He is a Manager

Metal Industries, Ltd. He is Chief Engineer in the Track Technology

in the Track Technology Development Division at the RTRI in charge

Development Division in charge of rail welding. He holds a Master’sof track geometry and maintenance.

degree in Welding Engineering from Osaka University.

Copyright © 1998 EJRCF. All rights reserved.

Japan Railway & Transport Review • March 1998

45