(Edited by Kanji Wako) The Mechanism of Railway Tracks

38 Japan Railway & Transport Review • March 1998

Technology

Tec hn o logy

Copyright © 1998 EJRCF. All rights reserved.

Railway Technology Today 2 (Edited by Kanji Wako)

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

Railway Operation in Japan

The history of railways in Japan dates backto September 1872 when commercialoperation started over a 29-km track be-tween Shimbashi (Tokyo) and Yokohama.Japan has achieved a tremendous devel-opment, both social and economic, overthe following 125 years, and railwayshave been no exception. The railway net-works in this relatively small land totalover 27,000 km, and up to 2.2 millionpeople ride trains each day. The fiveshinkansen lines stretch 2200 km withoperating speeds of 260 to 300 km/h.Shinkansen cover the 515-km stretch be-tween the two largest cities, Tokyo andOsaka, in 2 hours and 30 minutes. Thehigh efficiency of railway transportationputs railways ahead of air transport in Ja-pan, where the dense population is scat-tered along the Pacific coastal plain.The progress of railways and their role insociety is supported by new technologi-cal achievements in many areas. Safety,speed, and ride comfort have always beenmajor concerns for Japanese railway com-panies. The other major concerns today

are reducing noise pollution for peopleliving near tracks, and preserving the natu-ral environment. More recently, easiermaintenance has become an importantissue due to labour shortages and the needfor higher efficiency.Track is one of the most important techni-cal elements in railway operations. Tracktechnology has developed in parallel withthe railway itself. Current concerns of rail-ways are also technical issue for tracks.This article discusses the present status oftracks in Japan, and the future outlook.

Structural Analysis of Tracks

Basic structureJapan is a mountainous archipelago withnarrow coastal plains. Consequently,Japanese railways have many sharpcurves, tunnels, embankments, and steepgrades. The first railway in Japan was builtusing a narrow gauge (1067 mm) to meetthese geographical conditions and theneed for economy; the narrow gauge be-came the standard for all state-owned rail-ways until the first shinkansen in 1964.Figure 1 shows that railway track consists

essentially of rails and sleepers, laid in andfixed by ballast on a road bed. This eco-nomic design, which was chosen on thebasis of experience, has remained virtu-ally unchanged irrespective of other sub-sequent technical progress. Tracks arelong, large structures stretching hundredsor thousands of kilometers. In additionto economy, the design is a rational struc-ture for supporting heavy fast trains on softground. It is easy to maintain and offersoutstanding vibration and noise perfor-mance. 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 recentpreference for high-speed operations, re-quiring less maintenance. However, con-ventional ballasted track is still found onmore than 90% of railways in Japan.

RailsJapan’s first line used vertically-symmetri-cal, wrought-iron double-headed rails.They were soon replaced around 1880 byasymmetrical steel flat-bottom rails ofgreater toughness. These first rails weighed29.8 kilograms per meter (kg/m) and were7.3-m long. The weight and length werelater increased to carry more trains at fasterspeeds. Today, Japanese trains run on 50-or 60-kg rails. The 60-kg rails have thelargest cross-sectional area and are usedon all shinkansen tracks and other majorsections (Figure 2).The standard rail length is 25 m, but con-tinuous-welded rails (CWR), or long rails,are used on main sections to improve ridequality and reduce noise and vibration.The CWR is subject to compression loadsdue to temperature changes, which cancause buckling, or sharp lateral displace-ment. These phenomena are preventedusing reinforced fastenings, sleepers andballast.

Ballast (stone)

Source of vibration

Rail

Rail fastening

Rubber padSleeper

(a) Structure (b) Function

Weight of rail

Vibration blocked by fastening spring

Vibration absorbed by rubber pad

Weight of sleeper

Vibration absorbed by stone friction and spring action

Figure 1 Basic Structure and Function of Railway Tracks

39Japan Railway & Transport Review • March 1998Copyright © 1998 EJRCF. All rights reserved.

WeldingContinous-welded rails are being pro-moted in Japan to cut noise, vibration, andmaintenance costs. Rails can be weldedend-to-end using any of four processes:flash butt, thermit, gas pressure, and en-closed arc. Japan is unique in using thegas pressure process and the enclosed arcin addition to the other two, commonlyused in other countries.In 1996, the JR group completed about79,000 welds; 40% were by thermit weld-ing, 26% by gas pressure, 25% by flashbutt, and 9% by enclosed arc. The gaspressure process is less efficient than theflash butt process, but it is widely usedfor both factory and track-side welding

because the equipment is easily portableand the joint quality is as good as that ofthe flash butt process.

SleepersThe sleepers binding the rails were usu-ally made of hardwood timber. Concretesleepers, 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 easierto handle than concrete sleepers, theirmain drawback is short service life due todeterioration. Synthetic sleepers made ofhard polyurethane foam and glass fiberare a recent unique development in Ja-

pan. They are designed for long servicelife (more than 60 years) while maintain-ing the physical properties of wood sleep-ers. They are being used increasingly oversteel girder bridges, switches, and othersections where maintenance or replace-ment is difficult.‘Ladder sleepers’ are another on-goingdevelopment. They consist of 12-m longpre-stressed longitudinal concrete mem-bers bound by lateral steel tubes like aladder. The rails are supported continu-ously on the concrete members, whichdistribute the load lengthwise, reducingthe need for ballast maintenance.

Rail fasteningsIn the early days, dog spikes or othersimple devices were used to fasten the railto timber sleepers. With the introductionof concrete sleepers, the spikes were re-placed by double elastic fastenings inwhich the rail is fastened by a spring us-ing rubber pads or other cushioning ma-terials inserted between the rail andsleeper. Rail fastenings distribute load anddampen vibration and are an essentialcomponent in high-speed train operation.Leaf springs are used in Japan primarilybecause of cost and adjustability, and inFrance because of fastening force andbearing ability. Wire springs are preferredin Germany because of fastening force

140

68 72.561

1:9 1:10

32 32.5

CLCL

32.5 32.5

77.5

63.5

4173

.525

.5

4974

153

30

160

88.25

4687

.526

.5

4994

.9

1 :4 1:4

174

1 :41:4

1:2.751:2.75

1:2.751:2.75

30.1

60kg rail40N rail 50N rail 50T rail(Unit: mm)

Figure 2 Typical Rail Cross Sections

Gas pressure track-side welding (RTRI) Newly-developed ‘Ladder Sleepers’ (RTRI)


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and adjustability (Figure 3).

Shinkansen track structureThe Tokaido Shinkansen began operationin 1964 between Tokyo and Osaka at amaximum speed in excess of 200 km/hfor the first time in the world. When theline was first envisaged, there were twoplans for the gauge. One was to increasethe transport capacity by adding narrow-gauge double track to the existing TokaidoLine. The other was to increase the ca-pacity while halving the journey time bybuilding a standard-gauge double-trackline. The latter plan was eventually cho-sen, and the new line took a different routefrom the old Tokaido Line with many via-ducts, embankments, and tunnels andwithout level crossings.New rails, sleepers, and fastenings weredesigned for the high-speed line. TheTokaido Shinkansen track features:• 1435-mm standard gauge• CWR and concrete sleepers throughout• Movable nodes eliminating gaps at turn-

outs 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 laterentirely replaced by 60 kg/m rail)

The Tokaido Shinkansen was soon fol-lowed by the Sanyo, Tohoku, Joetsu andHokuriku Shinkansen built from 1972 to1997. The maximum speed was raisedfrom the initial 210 km/h to a more re-cent 260 to 300 km/h. Around 1967, ef-forts were started to develop slab tracksto prepare for the expected sharp increasein transport demand and higher operationspeeds. Slab track was first introducedon the Shin-Osaka to Okayama sectionof the Sanyo Shinkansen which startedoperation in 1972. Today, it is the stan-dard track bed for shinkansen. Figure 4shows the proportions of ballasted andslab tracks used on each shinkansen.

Shinkansen 102 Leaf Spring TGV Nabla Leaf Spring

ICE Vossloh Wire Spring

Figure 3 Different Rail Fastenings

Hokuriku

Ballasted track

Slab track

Trac

k d

ista

nce

(km

)

Tokaido Sanyo JoetsuOmiya – Niigata

TohokuOkayama –

HakataShin-Osaka –

OkayamaTokyo –

Shin-OsakaTokyo –

MoriokaTakasaki –

Nagano

0

200

400

600

516(100%)

0(0%)

156(95%)

8(5%)

125(31%)

273(69%)

15(5%)

255(95%)

48(10%)

453(90%)

20(16%)

105(84%)

Figure 4 Proportions of Ballasted and Slab Tracks on Shinkansen

(RTRI)


Slab Tracks

Slab versus ballasted tracksAbout 30 years ago, European railwayengineers in countries with advanced rail-way technology were examining car andtrack systems for trains running at speedsover 200 km/h. Their main concern waswhether it would be possible to repair thetrack ballast frequently enough before itwas loosened by the severe impact of thehigh-speed train operation. At that time,Japan decided to use ballasted tracksbased on the then new theory of ‘optimi-zation of ballasted track considering main-tenance requirements’—a wise decisionlater borne out by the success of theTokaido Shinkansen. The French andGerman railway operators had slightlydifferent views about this issue. In France,it was thought that speeds over 200 km/hwere possible on ballasted tracks, but inGermany, it was thought that althoughballasted track could endure speeds upto 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 515km/h—both records were on ballastedtracks. Meanwhile, in Japan, the highestspeed at that time of 425 km/h wasreached in December 1993 on slab tracksof the Joetsu Shinkansen. The currentspeed record in Japan is 443 km/h estab-lished on ballasted track on the TokaidoShinkansen by the experimental 300Xshinkansen belonging to JR Central.

Structure of slab tracksA slab track means a reinforced concrete(RC) slab laid on a viaduct or other rug-ged bed, and secured to the bed usingcement asphalt (Figure 5). Developmentof slab tracks began in 1965 and, aftermany experimental installations, theywere used in commercial operation for the

first time on the section between Shin-Osaka and Okayama on the SanyoShinkansen. Today, slab track is the stan-dard on concrete bed sections such asviaducts and tunnels. Slab tracks are alsobeing used experimentally on theearthwork section between Takasaki andNagano of the Hokuriku Shinkansen (pres-ently called Nagano-bound Shinkansen)which began operation in October 1997.

Economy of slab tracksA 1990 comparison of the economic mer-its of ballasted and slab tracks on theTohoku Shinkansen shows that slab trackconstruction costs 1.3 times more thanballasted tracks. However, this differencebalances out after about 9 years due thelower maintenance costs of slab track.Since slab track is lighter than ballastedtrack as a whole, the construction cost of anew railway based on slab track, includ-ing the viaduct cost, can be less in certain

cases. The same holds true for tunnel sec-tions because the lower track height re-duces the tunnel cross-sectional area,cutting construction costs by about 30%.This alone is more than likely to offset thedifference in construction costs betweenslab-track and ballasted-track railways. Asa result, some people claim that slab trackis more advantageous.

New Track Designs

Labor-saving track designsfor existing linesIt is generally thought that the followingmeasures minimize normal track subsid-ence:• Increasing track rigidity or using larger

sleepers• Increasing track elasticity• Increasing binding of bedThe photograph on the next page shows

a) Near slab centre

b) Near slab end

c) Near stopper

Slab

Cement asphalt

Concrete structure

Stopper Slab

Cement asphalt

Concrete structure

Stopper

Figure 5 Structure of Slab Track


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

Vibration-reducing tracksA growing social concern is protecting thetrack-side environment and residents frompollution problems caused by faster trainoperations or construction of projectedshinkansen. Protection from vibration andnoise is particularly indispensable. In-creasing operation density and other ele-ments are causing growing problems,making it more difficult than ever to main-tain normal conditions. Easing the needfor maintenance work is also a necessity.The photograph below shows the newly-developed solid-bed track with removable

resilient sleepers. In addition to havinganti-vibration performance, the sleeperscan be replaced easily when elastic fa-tigue occurs.

High-speed turnoutsEarlier shinkansen used 1:18 turnoutsbecause the operation modes did not re-quire high-speed turnouts. However, thenew Hokuriku Shinkansen uses a newly-developed 1:38 turnout because the newline branches off the Joetsu Shinkansen atabout 3.3 km from Takasaki Station. Thisnew turnout has a lead curve radius of4200 m, an overall length of approxi-mately 135 m, and a high turnout sidespeed of 160 km/h.

Track Maintenance

Need for track irregularitycontrolThe frequent passage of trains on tracks,especially ballasted tracks, loosens anddeforms the ballast and/or the bed sup-porting it. This leads to minor irregulari-ties and bending (collectively referred toas track irregularity). In addition, frequenttrain 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 behaviourvaries with the nature of the irregularity.A carriage is typically comprised of threeelements: body, truck, and axles (Figure6). Each element has a unique naturalfrequency affecting movement. A slowchange in track irregularity over a longspan (known as a long-wave track irregu-larity) mainly affects the vertical and lat-eral body vibration resulting in a poor ride.A short-wave track irregularity (rail sur-face 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-

Labour-saving E-type paved track (RTRI)

Newly-developed solid-bed track with removable resilient sleepers (RTRI) High-speed turnout (1:38) (RTRI)


2500 2500

17500

25000

5000 50002500

(a) Current Three-truck Car

(b) Planned Two-truck Car

Laser gyro unit

Digital operator

Laser reference unit (under floor)

Optical rail displacement sensor

larity. The passengers feel thrown towardsthe outside of the curve due to the unbal-anced centrifugal force which depends onthe speed. In addition, a large reactionforce is applied to the rail, causing thetruck to rotate along the curve. These fac-tors increase the burden of track mainte-nance. A large, lateral track irregularitycan even cause derailment due to climb-ing 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 sur-face irregularity must be established, andthe track must be inspected accordinglyat regular intervals, to maintain safety andride quality, and to minimize dynamicloads, noise and vibration.

Role of track inspection carsControl of track irregularity is performedat regular intervals and consists of: (1) in-specting track condition, (2) assessing re-pair need, (3) planning repair, (4)repairing, and (5) confirming repair work.The track inspection car plays an impor-tant role in inspecting the track condition,pinpointing sections requiring repair, andconfirming the repair work.Track inspection cars such as the narrow-gauge model built in the 1960s and theshinkansen model nicknamed ‘Doctor Yel-low’ (JRTR 11, front page) built in the1970s, simultaneously measure the tracksurface 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 align-ment method’) requires a special car withthree trucks. In addition, the design limitsthe maximum speed to around 200 km/h.These limitations called for developmentof new track inspection cars allowinghigher maximum speeds (for shinkansentracks), lower costs, and multiple functions(for conventional tracks).These needs are currently being met bydeveloping a two-truck track inspectioncar for shinkansen tracks with a maximum

speed in the range of 300 km/h, approach-ing that of commercial trains. The newinspection car uses three of its four axlesto obtain data that are converted to simi-lar data to those obtained by the earlierthree-truck car. It also features laser-basedequipment, a lightweight optical sensor

for measuring rail displacement, a high-performance gyroscope, and other tech-nologies (Figure 7).Similar developments are also under wayfor an entirely new low-cost track inspec-tion car for narrow-gauge tracks. This newsystem computes displacement from eas-

Long-wave track irregularity tends to cause body vibration

Short-wave track irregularity tends to cause wheel vibration

Riding comfort

Wavelength

Amplitude

Wavelength

Amplitude

Vibration model of railway car

Body

Truck

Wheelandaxle

Axle weightfluctuation,

and vibration

Figure 6 Wavelength of Track Irregularity and Car Movement

Figure 7 Design of Track Inspection Cars


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ily-measured acceleration; it also featuresother non-contact equipment, such asoptical and electromagnetic displacementsensors.

Track irregularity control indexesRide quality is noticeably affected by long-wave track irregularity; passenger cars onboth shinkansen and conventional linestend to sway at a frequency of 1.0 to 1.5Hz. The track irregularity wavelength in-ducing this sway frequency correspondsto 60–80 m at about 300 km/h onthe shinkansen, or 30–50 m at about 160km/h on conventional lines (Figure 8).However, the current 10-m chord align-ment method is designed primarily for in-specting 10- to 20-m track irregularity, not

for longer irregularities. Consequently, theJRs generally use a 40-m chord alignmentmethod for shinkansen and a 20-m chordalignment method for conventional lines.These methods have a better correlationwith carriage behaviour, contributing toeasier data processing and easy-to-iden-tify control indexes.The car’s lateral behaviour or ride qualityon curves is affected by two factors: theunbalanced centrifugal force which de-pends on the cant and the train speed, andthe lateral motion due to track irregular-ity. Ride quality evaluation taking thesefactors into consideration is used to de-termine the alignment maintenance tar-get for curves.Climbing derailment is caused primarily

by alignment irregularity and twist. Theformer increases transverse pressure,while the latter lifts wheels due to rela-tive twist between the truck and the track.Until the 1970s, multiple-cause freight carderailments were quite common. Theywere found to be due to level irregulari-ties inducing car rolling, and alignmentirregularity causing increased lateral thrustand attack angle. Based on these find-ings, compound track irregularity was setas a new control index. Freight car de-railments due to multiple causes de-creased significantly with improvedcarriage performance and stricter inspec-tion based on the new control index.Shinkansen wheel-rail noise during high-speed operation primarily refers to roll-ing noise, occurring when sound isemitted as a result of vibration of thewheel and the rail due to minor irregu-larities between them. Therefore, rollingnoise can be reduced effectively by grind-ing out rail surface irregularities. Rail sur-face 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 wav-ing wear of the rail cause rolling noise,increased vertical vibration of the wheel,and track deterioration. These irregulari-ties must be located and corrected by railgrinding. Rail surface roughness can beinspected directly but is inefficient due tothe slow measurement speed. As a re-sult, a new inspection method has beendeveloped using axlebox vertical vibra-tion acceleration, which has a close cor-relation with fluctuation in the load onwheels of passenger cars. This methodmore efficiently identifies trouble spotscausing such fluctuations.

10 mm

10 mm

10 mm

0.20 g

100 m

40 m

10 m

10-m chord alignment

40-m chord alignment

Restored alignment

Lateral acceleration

Low correlation between track irregularity and vibration

Vibration is emphasized

Actual track irregularity on ground

Irregularity causing motion

40-m chord

10-m chord

Figure 8 Waveforms of Track Irregularity and Shinkansen Car Behaviour


Masao Uchida

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

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

in the Track Technology Development Division at the RTRI in charge

of track geometry and maintenance.

Yasuto Fukada

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

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

Development Division in charge of rail welding. He holds a Master’s

degree in Welding Engineering from Osaka University.

Shigeru Miura

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

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

General Manager of the Track Technology Development Division at

the Railway Technical Research Institute (RTRI) where he is a lead-

ing engineer specializing in track dynamics and structure.

Hideyuki Takai

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

degree in Civil Engineering from the Tokyo Institute of Technology.

He is a Manager in the Track Technology Development Division at

the RTRI in charge of track structure and components.

Use of track irregularity dataTrack irregularity data obtained by a trackinspection car can be converted into digi-tal data, combined with track environmentdata and stored in a database. A trackmaintenance database system called ‘mi-cro-LABOCS’ (Figure 9) is commonly usedto store these data. It calculates track sec-tion evaluation indexes and long-wavetrack irregularity, analyses the track irregu-larity wavelength and relationship withcar behaviour, and identifies long-termchanges in track irregularity.The system provides a restored waveformcalculated from 10-m chord alignmentdata that accurately represents the actualtrack profile over a limited waveband (forexample, 6–100 m). This is comparedwith the track design profile and trackmaintenance is performed to restore thedesign track alignment. Efforts are cur-rently under way to coordinate this sys-tem with an automatic control system fortamping machines to introduce a com-pletely new dimension in fully-automatedtrack maintenance. �

Figure 9 ‘micro-LABOCS’ Track Maintenance Database System

Kanji WakoMr 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 this

new series on Railway Technology Today.

Trackinspection

car

(Edited by Kanji Wako) The Mechanism of Railway Tracks

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