Technology

Technology

Railway Technology Today 9 (Edited by Kanji Wako)

Protecting the Trackside Environment
By Tatsuo Maeda

More and more people are calling formeasures to protect the environment, andenvironmental degradation caused byrailways is also a matter of concern. It is
now well recognized that train speeds
cannot be raised further without firstconsidering how the extra speed might
negatively impact the environment. Anyplan to increase operating speeds must
include an assessment of the possible
environmental problems, and steps must
be taken to ensure that problems do notarise.
Environmental problems associated withrailways include: track noise, micropressure waves generated at tunnels,pressure variations caused by passing trains,ground vibrations, radio interference, andshade cast by railway structures. This
article looks at the first four problems, anddiscusses how technology can be applied
to alleviate them to some degree.

Table 1

Environmental Standards
for Shinkansen Noise

Category

Standard

I

70 dB(A) max.

II

75 dB(A) max.

Notes: I = Mainly residential areas
II = Other areas for ordinary
economic (commercial andindustrial purposes) activities

Table 2

Railway Noise
Environmental quality standards
governing shinkansen noise andcomplianceJapan’s rapid economic growth in the
1960s had a severe impact on theenvironment. As a countermeasure, thegovernment enacted the Basic Law forEnvironmental Pollution Control in 1967.
This law remained in effect until adoptionof The Basic Environment Law in 1993.
Between these two dates, in 1975, theEnvironment Agency announced newenvironmental standards directive forshinkansen railway noise (Table 1). Thesestandards, which were based on the 1967
law set the maximum noise level at 70
dB(A) for Category I (mainly residential
areas), and at 75 dB(A) for Category II(non-Category-I areas used for ordinary
economic activities, such as commercial
and industrial activities). It is important
to note that the Prefectural governors candetermine category designations.
The government also defined how noise
measurements were to be conducted, andhow the results were to be evaluated.
Measurements must record the peak noiselevels of 20 shinkansen trains passing ineach direction consecutively. The
measurements are taken outdoors withmeasuring instruments 1.2 m above theground in places known to have highvolumes of railway noise, and where noisefrom shinkansen is deemed to be causing
problems. The measurements are
conducted during normal weather
conditions when trains pass themeasurement point at normal speeds.
The shinkansen railway noise should be
evaluated by the energy mean value ofthe higher half of the measured peak noiselevel. The measuring instruments usedshall be a noise meter with A-weighted
calibration and slow dynamic response.
The 1975 directive issued by the Environment Agency allowed for a grace period
before the railway had to comply with thestandards (Table 2). When the permissiblelevels were drawn up, two shinkansen
lines were already in operation (Tokaido
and San’yo), two others were underconstruction (Tohoku and Joetsu), and morelines were in planning. Lines alreadyconstructed and lines under construction
were granted a grace period before
compliance.
After these provisions were adopted, therailway implemented a variety ofmeasures to reduce noise levels along
shinkansen tracks. In 1991 and 1994, theEnvironment Agency conducted surveys
to determine the extent of compliancewith the 75 dB(A) standard in first-priority
areas (Table 3).
The 210 km/h maximum speed forCompliance Deadlines for Shinkansen Noise
Compliance Deadline

Permitted Noise Level for Trackside Zones
Zones with permitted level of 80 dB(A) or more
Zones withpermitted levelof >75 to <80dB(A)Track under construction

3 years max.

At start of operations

Areas contiguous with Category-I areas

Within 7 years

Areas not contiguous with Category-I areas

Within 10 years

Zones with permitted level of >70 to ≤75 dB(A)48

Track already built

Japan Railway & Transport Review 22 • December 1999

Within 10 years

Within 3 years after start of operations

Planned track

At start ofoperations

Within 5 years after start of operations

Copyright © 1999 EJRCF. All rights reserved.

Compliance with 75 dB(A) Standards for First-Priority Track Sections

TokaidoSan’yoTohokuJoetsu

Total

Items
Number of measurement sites
Average noise level (dB(A))
Percentage of sites registering ≤75 dB(A)
Number of sites measured
Average noise level (dB(A))
Percentage of sites registering ≤75 dB(A)
Number of sites measured
Average noise level (dB(A))
Percentage of sites registering ≤75 dB(A)
Number of sites measured
Average noise level (dB(A))
Percentage of sites registering ≤75 dB(A)
Number of sites measured
Average noise level (dB(A))
Percentage of sites registering ≤75 dB(A)shinkansen in 1975 had risen to 270 km/h
by 1994, but the surveys found no noncompliance along the Tohoku or Joetsu
shinkansen lines. The current maximum
speed for Series 500 rolling stock on the
San’yo Shinkansen is 300 km/h, while thatfor other shinkansen trains is 270 km/h,
but it is very rare for noise levels to exceed
75 dB(A) anywhere on these lines.
Indeed, on some sections of the Naganobound Shinkansen, 3-m high soundbarriers keep noise levels below 70 dB(A).

Shinkansen noise components
Before attempting to reduce train noise, wemust first identify the various sources andwe must determine how much eachcontributes to the overall noise at themeasuring points. In the case of
shinkansen, noise can be classified as
pantograph noise, aerodynamic noise
generated by the car bodies, running noise
generated from the underbody, and noisefrom concrete structures.
Pantograph noise includes aerodynamic
noise generated at the pantograph andpantograph shield, frictional noise causedby the collector running on the catenary,

Copyright © 1999 EJRCF. All rights reserved.

1991

1994
120

73.4
78

72.1
98
62

73.1
84

Microphone array

72.3
98

Figure 1 Noise Level History fromMicrophone Array

26
75.8
50

72.9
100
15

74.1
67

(RTRI)

71.0
100

223
73.7
72.2
76
98
(Environment Agency)

and sparking noise between the collector
and catenary. Aerodynamic noise
generated by the car bodies is caused by
the flow of air over the carriage outersurface and includes noise generated at thetrain nose, cable head, window louvres, airconditioning equipment, and the gaps
between cars. Running noise is generated
from the underbody and includes therolling noise of wheels on rails, gear noise,
noise generated by bogies turning slightly
under the carriages, etc. Noise fromstructures is emitted from the lower surfaceof the concrete elevated track.
A microphone array is used to identify theextent to which each source is contributing
to the overall noise. Each microphone in
the array is positioned to register specifichalf-wavelength intervals in each frequency
band. A special directivity is given byweighting each microphone’s output andcalculating the aggregate. The MY-10
microphone array directivity is such that it
is possible to distinguish sounds over aplane width of about 6 m, with the soundarriving from 25 m. Figure 1 shows a noiselevel time history for shinkansen noise
recorded by this array. To determine thePantographs

10dB

Shinkansen Line

A-specific sound pressurelevels (dB(A))

Table 3

1-second interval

extent to which each noise source
contributes to the overall noise pattern, thehigh and low values in the noise level time
history are used, and the noise sources areapproximated to non-directional noise
sources with fluctuating power densities
within each 12.5-m interval.
Pantograph noise contributes much moreto the noise at the ground-based measuring point than any other noise source
within the same plane. For all intents andpurposes, the only factor contributing tonoise emitted when a pantograph passes
a specific place is pantograph noise.
The microphone array does not havevertically oriented microphones, so itcannot differentiate vertical sounds.
Therefore, the level of noise generated fromthe underbody is measured close to the rail
and the measurements are evaluated in a
way that separates aerodynamic noises
generated by the car body from noises fromthe underbody.
Noise from concrete structures is mainlycomposed of frequencies below 100 Hz
that cannot be picked up by a microphonearray located some distance from thetracks. Therefore, the noise levels ofJapan Railway & Transport Review 22 • December 1999

49

Technology

Figure 2 Relative Importance of Shinkansen Noise Sources and Results of Noise Countermeasures75

75dB(A)
79.5dB(A)75
73

1982: A ➞ B
1985: B ➞ C
1985: C ➞ D
1986: D ➞ E
1992: E ➞ F
1992: F ➞ G
1992: G ➞ H

;;;;
;;;;;
72.5

1997: H ➞ I

77.5

E'

F'

G'

H'

Rail grinding
Bus cables
Speed increase (from 210 to 240 km/h)
Pantograph shields
Aerodynamic carriage design
Speed increase (from 240 to 270 km/h)
Low-noise pantographs and aerodynamic
carriage design
Speed increase (from 270 to 300 km/h)

I'

;;
;;
;;
;;
;;
;;
;
;;
;;
;;;
;;
;;;;
;;;;;
77

74

Spark noise

76

76

76

Pantograph noise

74.5

74

Aerodynamic noisefrom carriage body

Noise from carriage
underbodyNon-pantograph noise

Concrete structure noise

A

B

C

D

E

F

G

H

I

Measured at ground level, 25 m from concrete elevated track, 8 to 10 m from ground level to rail level with slab track
Cases A to I: Track with straight noise barrier (2 m higher than rails)
Cases E’ to I’: Track with inverse L-type noise barrier (sound-absorbing material, 2 m higher than rails)

concrete structure, are evaluated bymeasurement using a microphone directly
under the elevated track structure.
Sound analyses show that:• Aerodynamic noise is proportional to
the sixth power of train speed• Wheel and rail rolling noise is proportional to the second or third power oftrain speed• Concrete structure noise is proportional to the second power of train
speed
Parabolic directional microphones arealso used to analyze sound contributions
more precisely.

Reducing impact of shinkansen
noise sources
Parabolic directional microphones

50(RTRI)The noise analysis method described above

Japan Railway & Transport Review 22 • December 1999

is used to determine the extent to which
each noise source contributes toshinkansen noise, and to determine theeffectiveness of each noise-reduction
countermeasure. Some results are shownin Fig. 2. The measurement point was at
ground level, 25 m from the centre of theconcrete elevated track structure, 8 to 10 m
below the track level. A 2-m high soundbarrier had been installed. In cases A to I,
the barrier is a straight barrier, while in cases
E’ to I’, it is an inverse L-type barrier withsound-absorbing materials.
In cases A, B and C, the train speed was
210 km/h. Case B (1982) shows
improvement over A because the rails had
been smoothed by grinding to reducerolling noise, which is the main componentof underbody noise. Case C (1985) shows

Copyright © 1999 EJRCF. All rights reserved.

improvement over B because bus cables
had been installed between pantographs
to reduce sparking noise. When bus cables
are installed, even if one pantographbounces off the catenary, current still flows
through the other pantograph, preventing
sparks.
In case D (1985), shinkansen speeds had
been increased from 210 to 240 km/h,
explaining why noise levels increased
over case C. In cases D, E and F, the train
speed was 240 km/h. Case E (1986) shows
an improvement over Case D, because
pantograph shields had been mounted toreduce pantograph noise. The shields
reduce the speed of the air flowing aroundthe pantograph, reducing aerodynamic
noise generated by the pantograph itself
and muffling any aerodynamic noise
emitted by the pantograph. Case F (1992)
shows an improvement over E, because
the smoother aerodynamic exterior of therolling stock reduced the noise.
In case G (1992), shinkansen speeds had
been increased from 240 to 270 km/h,
explaining why noise levels increased overcase F. Case H (1997) shows improvement
over case G, because a low-noise
pantograph and smoother rolling stock
exterior had been adopted, cutting down
on both pantograph and aerodynamic
noise.
Train speeds were increased with thesurprising result that large pantographshields themselves became a source of
aerodynamic noise. To overcome thisproblem, a low-noise pantograph wasdeveloped, and the pantograph shield was
reduced in size to the point that it shields
only the pantograph insulators. In case I

Table 4(1997), shinkansen speeds had been
increased from 270 to 300 km/h, but on
track sections with an inverse L-type noisebarrier made of sound-absorbing
materials, the sound intensity is no higher
than 75 dB(A).
When the Tokaido Shinkansen was
inaugurated in 1964, the noise level for
Series 0 rolling stock was 90 dB(A) at train
speeds of 210 km/h. Clearly the
aforementioned changes over the last 35
years have yielded huge improvements.

Environmental guidelines onnarrow-gauge lines

Low-noise pantograph and insulator cover on Series
500 shinkansen(JR West)

Tunnel Micropressure Waves

In response to recent public concern overnoise pollution, in 1995, the Environment
Agency issued guidelines for noise levels
on narrow-gauge lines (Table 4). The
guidelines specify a maximum of 60 dB(A)during the day and evening (0700 to 2200)
and 55 dB(A) at night for equivalent noiselevels (LAeq) on newly constructed lines.
The guidelines also call on railways toreduce noise levels further in residential
areas, especially residential-only zones.
Furthermore, when railways makesignificant modifications to existing
tracks—for example, double or quadruple
tracking, or construction of long elevatedsections at crossings—the noise levels
must be lower than before themodifications. The guidelines do not
clearly specify noise levels on existingt r a c k s . H o w e v e r, t h e p u b l i c i s
increasingly unwilling to tolerate railway
noise, so railway companies must clearly
identify the various noise sources anddevelop affordable countermeasures.

Effect of tunnel micropressure
waves
Trial runs on the San’yo Shinkansen in
March 1975 resulted in protests fromresidents living along the track because
their doors and windows were vibratingfrom explosion-like sounds generated
when shinkansen trains passed throughlong tunnels on slab track. This new noiseproblem had not been seen before.
The sound is caused by compression
waves that are generated when a train
enters a tunnel at high speed. Thesecompression waves propagate at the
speed of sound through the tunnel and apart of them is changed into pulse pressure
waves radiated from the tunnel exit. These
pulse pressure waves are calledmicropressure waves. In Japan, tunnel
micropressure waves are considered to bea low-frequency vibration problem,
because they are pulse waves and include
low-frequency components. Japan still
has no environmental standards or

Guidelines for Maximum Railway Noise on Narrow-Gauge Lines
New lines

Large-scale upgraded lines

Copyright © 1999 EJRCF. All rights reserved.

Equivalent noise levels (LAeq) of 60 dB(A) max. from 0700 to 2200 and 55 dB(A) max. from
2200 to 0600). Special efforts to reduce noise levels in residential areas.
Noise levels must be lower than before upgrade.

Japan Railway & Transport Review 22 • December 1999

51

Technology

guidelines covering these tunnel
micropressure waves.
The tunnel micropressure wave effect has
three phases: generation of compression
waves when the train enters the tunnel,
propagation of compression waves throughthe tunnel, and radiation of micropressure
waves from the tunnel exit (Fig. 3).
The micropressure wave peak ischange is inversely proportional to the train
velocity at the tunnel entrance.
The pressure gradient of the compression
wave front propagating through the tunnel
varies with the track structure. In a tunnel
with slab track, the wave’s non-linear
effect is greater than the friction exerted
by the tunnel walls and track, so the wave
front is steeper, creating a steeper pressure

approximately directly proportional to thepressure gradient of the compression wave
front exiting the tunnel. At the tunnel
entrance, the pressure gradient ofcompression wave front is approximately
directly proportional to the cube of the train
velocity, because pressure increases as thesquare of the train velocity at the tunnel
entrance, while the time for the pressure

Figure 3 Tunnel Micropressure Wave EffectTunnel portal

Generation ofcompression wave

Radiation of
micropressure wave

Propagation ofcompression wave

U

TunnelportalTunnel

∆p

∆p

Train

x

Figure 4 Tunnel Micropressure Waveformx

Figure 5 Effect of Tunnel Length and Track Type on
Peak Micropressures
500
Measured 20 m from tunnel portal

150

200

Max. micropressure (Pa)20 m from tunnel portal

Pressure (Pa)100
U = 197 km/h

U = 167 km/h

50

100
V3 Rule50

20
10Tunnel with slab track (1660m)
Tunnel with slab track (6822m)

0

5
0.1 s

Tunnel with ballast track (723m)

Time

Tunnel with ballast track (3989m)
2
160

180

200

220

240

260

280

Velocity (km/h) of train at tunnel entrance

52

Japan Railway & Transport Review 22 • December 1999

Copyright © 1999 EJRCF. All rights reserved.

Figure 6 Relationship between Length of Tunnel Hoodand Micropressure Wave Reduction

Figure 7 Effect of 49-m Tunnel Hood on Micropressure
Waves

1: On-site test
: Model experiments

0.8

0.9
0.6
0.8
0.4
0.7
0.6

0.2

0.5
0

0

10

20

30

Length (m) of tunnel hood40

Tunnel (6640 m) with slab track
Measured 20 m from tunnel portal
200
Max. micropressure (Pa)

Reduction in pressure gradient1

Reduction in train velocity at tunnel entrance

500

100
Without hood
50

20

10
With hood (49 m)

50

5
190

200

210

220

230

240

250

260

270

Velocity (km/h) of train at tunnel entrance

gradient. On the other hand, in a tunnel
with ballasted track, the wave’s non-linear
effect is smaller than the friction exerted
by the ballast, thereby reducing thepressure gradient of the wave front. This
explains why micropressure waves are notan issue on the Tokaido Shinkansen whichuses ballasted track for most sections.
Micropressure-wave-related noise
pollution only became an issue after
construction of the slab-track San’yo
Shinkansen.
In short tunnels, the peak value of a
micropressure wave is approximately indirect proportion to the cube of the train
velocity at the tunnel entrance, regardlessof track type. This is because pressure
gradient variations are not conspicuously
great during the propagation ofcompression waves. On the other hand,
track type is an important consideration
in long tunnels. In a tunnel with slab track,
the peak value for micropressure waves
exceeds the cube of the train velocity.
However, in a tunnel with ballasted track,
the peak value for micropressure waves
is smaller than it would be in a shorttunnel. The amplitude of micropressure

Copyright © 1999 EJRCF. All rights reserved.

waves emanating from the tunnel exit isinversely proportional to the distance fromthe tunnel entrance.
Figure 4 shows a typical micropressure
waveform, measured 20 m from the tunnel
portal. Figure 5 shows the effect thattunnel length and track type have on thepeak values. The horizontal axis in Figure
5 is the train velocity.
Micropressure waves cause a suddensound, rather like an explosion, before theStreamlined nose of Series 500 shinkansen

train exits a tunnel. These sounds are
viewed more negatively by the public thanother railway noises.

Countermeasures to micropressure
wavesCountermeasures involve modifying thedesign of both the tunnel and rolling stock.
The tunnel design can be modified in a
number of ways to diminish the wave frontpressure gradient by using:(JR West)

Japan Railway & Transport Review 22 • December 1999

53

Technology• Tunnel portal hoods to reduce thepressure gradient of the compression
waves• A shelter with slits between adjacenttunnels to permit escape of thecompression waves• Inclined or vertical shafts to bypass
compression waves
Rolling stock can also be designed toreduce the pressure gradient at the tunnel
entrance by reducing the cross-section
area and extending the train nose to the
optimum shape.

Tunnel entrance hoods
Tunnel entrance hoods are often used toreduce micropressure waves inshinkansen tunnels. The effect depends
on the hood length (Fig. 6). A typicaltunnel entrance hood has a cross-section
area of about 1.4 times that of the main
tunnel with openings in the sides. Model
experiments are often used to determine
which opening sizes and positions
minimize the pressure gradient in theactual tunnel.
As Figure 6 shows, when the train enters
the tunnel, a hood can reduce the pressure

gradient by 20%. Since the pressure
gradient at the tunnel entrance is in direct
proportion to the cube of the train velocity,a hood has the same effect as reducing
the train velocity by 60%.
Figure 7 shows an example of the
reduction in micropressure waves
achieved by a hood. Without the hood, a
train travelling at 250 km/h generates
micropressure waves of approximately
300 Pa—falling to 20 Pa with the tunnel
hood. This far lower level corresponds tothe pressure created by the same train
entering the tunnel at 150 km/h andensures that no explosive sound is heard
at the tunnel exit.

Optimum train nose shapePressure gradients can also be decreased
by reducing the cross-sectional area of cars,
but this diminishes space in the carriage,
so there is a limit to the usefulness of thismethod and most efforts are concentrated
on optimizing the shape of the train nose.
Model experiments show thatmicropressure waves are minimized by anose shape with a uniform longitudinal
section except at the extreme tip (Fig. 8).

Figure 8 Optimum Train Nose Shape

Some examples of these nose designs areused by the Series 500 shinkansen
operating at 300 km/h by JR West on the
San’yo Shinkansen, by the Series 700
shinkansen developed jointly by JR Central
and JR West, and by the E1 through E4
shinkansen operated by JR East.
Obviously, the nose design must also
reduce other negative aerodynamic
effects, such as pressure variations due topassing trains, aerodynamic drag, andaerodynamic noise.

Pressure Variations when
Trains Pass
Pressure variations occurring when trains
pass in opposite directions cause carriage
vibration and ride discomfort. They canalso cause vibration in the windows anddoors of trackside buildings. The
phenomenon occurs when the pressure
fields generated at the heads and ends ofthe moving trains shift in conjunction withthe forward progression. This is not awave phenomenon like micropressure
waves, but is a near-field phenomenon inwhich pressure decreases in inverse

Figure 9 Passing Train Pressure Variations

Sudden changes inlongitudinal sectional area
reduce effectCentre longitudinal section

When train ends pass

50Pa

Pressure

When train noses passTime
While pantographshields passing

Longitudinal
section area

Train speed 271 km/h;
measured 10 m from trains

Minimal changes in longitudinal
sectional area except at tip maximize effect

Length54

Japan Railway & Transport Review 22 • December 1999

Nose tip

Copyright © 1999 EJRCF. All rights reserved.

This hood at the entrance to Ohirayama Tunnel (6640m) on the San’yo Shinkansen is
49 meters long. If it had been constructed at the same time as the line, it would havebeen concrete.
(JR West)

proportion to the square of the distance
between the two trains. However, thephenomenon resembles tunnel
micropressure waves because it makes
windows and doors vibrate. In Japan,
these pressure variations are considered
to be a low-frequency vibration problem
and they are not covered by any
environmental standards or guidelines.
Figure 9 shows some examples of measured
pressure variations caused by passing trains.
If trains have large pantograph shields inConcrete tunnel hood at the Daini-arikabe Tunnelpressure shield walls on the track, andoptimizing the carriage longitudinal-section
area and nose shape.
Figure 10 and 11 show the results of onsite experiments on the effectiveness of
trackside pressure shield walls. The best
effect is achieved with higher walls close
to the track.
Pressure variations are less pronouncedwith rolling stock of smaller cross-section
area, but reducing the cross-section
area reduces space in the carriage.

the mid-section, the shields themselvescause pressure variations. The pressure
peaks are in direct proportion to the squareof train speed, while the time for thepressure is inversely proportional to train
speed.

Countermeasures to pressure
variations when trains pass
There are a number of possible
countermeasures to pressure variations
when trains pass, such as installation of

Figure 10 Pressure Shield Wall and Pressure Measuring Points(JR East)

Figure 11 Effectiveness of Different Pressure Shield Walls
10 3

6m

No pressure shield wall

0.5m

h

7m
10m

Max. pressure amplitude (Pa)h = 2.5m
h = 3.5m
h = 5.0m

10 2

13m
Measured values(calculated for train
travelling at 270 km/h)

23m
30m
10 1

7

8

9

10

20

30

Distance (m) from track centre

Copyright © 1999 EJRCF. All rights reserved.

Japan Railway & Transport Review 22 • December 1999

55

Technology

Aerodynamic simulations using the threedimensional boundary element method
show that the best effect is achieved when
the nose is more extended and has a twodimensional cross-sectional shape thatforces the air flow upwards.

Table 5Ground Vibrations
Guidelines on ground vibrations
and compliance
In 1976, the Environment Agency issued
guidelines on vibrations caused by

Guidelines on Vibration Caused by Shinkansen (received by
Minister of Transport from Environment Agency in 1976)

Guidelines(1) The railway must adopt prompt countermeasures to the source of shinkansen
vibrations and must prevent negative effects of these vibrations in areas where
increased speeds cause vibrations exceeding 70 dB.
(2) The railway must give special consideration to zones where tranquillity is important,such as hospitals and schools, with a view to reducing vibrations in these areas
as soon as possible.

shinkansen (Table 5). These guidelines
required that railways adopt measures todeal promptly with the sources of vibrations and to prevent the negative effectsof vibrations in areas where increased
speeds were generating vibrations exceeding 70 dB. Special consideration was also
to be given to zones where tranquillity isimportant, such as hospitals and schools.
Table 6 shows ground vibration levels
recorded along shinkansen tracks during
surveys by the Environment Agency in1987 and 1988. The maximum values
specified in the guidelines were notexceeded anywhere along the Tohoku andJoetsu Shinkansen, although some places
along the Tokaido and San’yo Shinkansen
did register values outside the guidelines.

Ground vibration countermeasures
Table 6
Shinkansen
Line
TokaidoSan’yoTohokuJoetsuGround Vibration Levels along Shinkansen Tracks(recorded by Environment Agency)
Items
Number of survey sites
Average vibration level (dB)
Number of sites exceeding guidelines
Number of sites surveyed
Average vibration level (dB)
Number of sites exceeding guidelines
Number of sites surveyed
Average vibration level (dB)
Number of sites exceeding guidelines
Number of sites surveyed
Average vibration level (dB)
Number of sites exceeding guidelines

Distance from Track
12.5 m
25 m
50 m
71
73
59
63
59
54
8
3
0
48
49
51
61
56
50
4
0
0
46
50
50
58
54
49
0
0
0
25
25
25
57
53
49
0
0
0

Figure 12 G-Type Slab Track

Rail
Rail fastening
SpacerConcrete roadbed

Track slab
Grooved slab mat
Cement/Asphalt (CA) Mortar

In order to save maintenance (labour)
costs, slab track was developed for the
San’yo Shinkansen west of Okayama.
However, slab track has higher noise andvibration levels than ballasted track
because the track springing is hard, theslab rigidity is high, and there is no ballast
sound absorber.
These noise and vibrations were reduced
by developing a vibration-isolation slab
track called the G-type (Fig. 12). Trackspringing was improved by placing
grooved slab mats under the slab in thegeneral area of the rails. In addition, afoam spacer with a low spring constant
was inserted in the gap in the centre of
the slab. This was effective in reducing
contact vibration and concrete structurenoise. Table 7 lists some general waysthat track can be modified to isolate
vibrations.
Carriage-related measures include:• Reducing car weight• Changing axle arrangement• Changing car spring configuration• Improving suppression of wheel flats
Track-related measures include:• Smoothing track surface

56

Japan Railway & Transport Review 22 • December 1999

Copyright © 1999 EJRCF. All rights reserved.

Table 7 Vibration Countermeasures

Carriages• Reduce car weight• Change axle arrangement• Change spring configuration• Control wheel flats• Smooth track surface• Soften track springing• Lengthen rails by welding; grind rails; control track irregularities• Install more resilient pads and vibration-reducing ties,
ballast mats, and slab mats; install solid-bed tracks withresilient ties
• Switch to heavier rails; install ladder ties; reinforce roadbed

Track• Increase track rigidity• Install floating-slab track

Concrete structures• Change to rigid massive structures• Use vibration-isolation devices• Use passive dampers• Use active/hybrid dampers• Control vibration direction

Ground• Dig vibration-breaking trenches• Install in-ground vibration-reducing walls• Install wave-impeding blocks• Improve ground• Tuned mass dampers, chained dampers• Foundation modifications (or rearrangements)• Use vibration-reducing structures
Dwellings, etc.

• Hard walls; soft walls; sandwich walls of hard and soft materials• Increase number of foundation slabs; insert additional posts
and beams• Use vibration isolation devices• Use dampers• Lowering elastic coefficient of trackpads• Increasing track rigidity• Using floating-slab track
Structure-related measures include:• Changing to rigid and massive structures• Using vibration isolation devices
Ground-related measures include:• Digging vibration-breaking trenches• Constructing in-ground vibrationreduction walls• Laying wave-impeding blocks• Improving ground

Conclusion
Any attempt to increase train speeds mustbe accompanied by efforts to deal withthe resulting increase in environmental
problems, such as railway noise, tunnelrelated micropressure waves, pressure

variations when trains pass, and groundvibrations. Unwanted environmental
phenomena must be anticipated and thecountermeasures must be comprehensive,
including new rolling-stock designs, better
track structures, and improved tracksidefacilities.
■

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

Tatsuo Maeda
In addition, dwellings and other buildings
can be made more vibration-proof by useof vibration dampers and vibrationisolation devices.

Copyright © 1999 EJRCF. All rights reserved.

Dr Maeda is Manager of Aerodynamics & Noise Reduction at RTRI. He joined JNR in 1974 after
graduating with a Masters degree in Aeronautical Engineering from Kyoto University.

Japan Railway & Transport Review 22 • December 1999

57