Railway elevated structure noise—A review

Journal of Sound and Vibration (1983) 87(2), 249-271

RAILWAY

ELEVATED

STRUCTURE

NOISE-A

REVIEWt

L. E. WITTIG Bolt Beranek and Newman Inc., 10 Moulton Street, Cambridge, Massachusetts 02238,

U.S.A.

(Received 24 May 1982)

This paper presents a review of recent work concerned with understanding and controlling the noise from railroad and rapid transit elevated structures. The basis of this paper is a study sponsored by the U.S. Department of Transportation (DOT), where the emphasis was on locating and analyzing the structures in the U.S.A. responsible for the greatest environmental noise impact. The parts of this study that are discussed include (1) development of a noise rating criterion, (2) a noise impact survey of elevated structures in the U.S.A., (3) an analytical analysis of the type of structure that is responsible for approximately 90% of the elevated noise impact in the U.S.A., and (4) a case study analysis that included a review of published data as well as measurements of two structures in the U.S.A. where noise control treatments were tested.

1. INTRODUCTION In the U.S.A. today there are approximately 260 km of elevated rapid transit structures. The maximum A-weighted noise level during the passage of a train on these structures often exceeds 100 dB(A) at 10 m, and frequently, at least for the older transit systems,

these structures are located in narrow streets lined with residential buildings. The problem is illustrated in Figure 1, which presents a sketch of the most common type of elevated structure in the U.S.A. Because the wheels and the rails are not perfectly smooth, vibrations originate from the wheel/rail interface, causing both the wheels and

Figure transmission

1. Schematic in air; -,

representation of noise generation vibration transmission in solids.

by train

t This paper draws heavily on reports written by Paul J. Remington, and Eric E. Ungar. Their works are cited in the list of references.

on elevated

Theodore

structure.

J. Schultz,

+#+,

Sound

David A. Towers,

249 0022-460X/83/060249+

23 $03.00/O

@ 1983 Academic

Press Inc. (London)

Limited

250

L. E. WI’ITIG

the rails to vibrate and radiate noise. In addition, the vibration energy in the rails flows to the deck and girders, and they in turn radiate noise. Undercar equipment is also a source of noise; the loudest of this equipment is generally the cooling fan on self-ventilated propulsion motors. Almost all of the older, noisier structures in the U.S.A. run above hard, reflecting streets, which causes a 3 dB increase in noise level, and in many cases there may be reflecting buildings on one or both sides of the structure. Because of the intense noise from these elevated structures and the proximity to them of many urban residents, the U.S. Department of Transportation (DOT) sponsored a study to quantify the problem and recommend solutions. This study had five major tasks: (1) development of a noise rating criterion; (2) an inventory of U.S. urban rail transit elevated structures; (3) development and implementation of analytical models; (4) case study analysis; (5) noise control design guide. In this paper the first three of these tasks are discussed. 2. NOISE RATING CRITERIA The purpose of this task was to recommend criteria for rating the noise radiated from elevated transit structures during train passages, so that different types of structures could be compared with respect to their noise impact on the immediate neighborhood, and so that noise abatement programs for elevated structures could be developed on a rational basis. A full description of this task has been presented in a DOT report by Schultz [ 11; this section presents only a brief summary of that report. The first step in this task was to examine the requirements for a suitable descriptor for rating the noise from elevated structures. In reality there are two different contexts in which the evaluation must be carried out. In some cases, one is interested in comparing the noise of different kinds of elevated structures, one against the other. This comparison is best made in terms of the average maximum A-weighted sound level during a train passby, because such rating focuses upon the noise-generating capability of the structure. The rationale for this approach was developed for the Department of Transportation (DOT) with respect to annoyance caused by wheel/rail noise of urban mass transit [2]. In other cases, one is interested in assessing how the noise of rapid transit trains on elevated structures compares with the noise impact on the community due to all other kinds of noise. For this purpose, in addition to the maximum passby level, one must take into account the number and duration of train passages, and put this information into a rating context that is general enough to accommodate all kinds of noise. Several potential candidates for the most suitable descriptor were considered. Some of these have been developed to rate the noise of a specific kind of source, such as the Traffic Noise Index (TN.), used for rating urban street traffic noise, or the Noise and Number Index (NNI), the Noise Exposure Forecast (NEF), and the Composite Noise Rating (CNR), all used in the assessment of aircraft noise near airports [3-51. Each of these ratings predicts reasonably well the subjective response to the kind of noise for which it was developed. However, because of the requirement that the descriptor must apply to all kinds of noise, these particularized ratings, validated only for specific sources, were eliminated from consideration. Noise Pollution Level (NPL) is a descriptor that was deliberately introduced to deal with both road traffic noise and aircraft noise, though not necessarily in combination. However, measuring NPL is rather complicated, and determining the NPL for combinations of noise sources is also quite difficult. Moreover, NPL has had only moderate success in correlating with the effects of noise on people. Thus, despite its early apparent attractiveness, NPL has not come into general use.

RAILWAY

ELEVATED

STRUCTURE

NOISE

251

Statistical descriptors, such as L 90, L 1o and L 1, have been used widely in the study of surface transportation noise. But, while these descriptors are useful in assessing noise exposure with “well-behaved” (i.e., quasi-Gaussian) statistics, they are quite unsuitable for railroad and aircraft noise, which are characterized by discrete, individual noisy events of relatively infrequent occurrence. The reason is that, no matter how loud the noisy events may be, unless their cumulative duration lasts for more thanX% of the observation period, they will have no effect whatever on the value of Lx. The environmental noise descriptor that correlates best with the three categories of cumulative, long-term effects of noise on people, while fulfilling the requirements for a suitable descriptor for elevated structures, is the long-term average sound level. The average sound level is the constant level of sound that, in a given situation and time interval, would expose the ear to the same amount of acoustical energy as does the actual time-varying noise pattern. The simple concept of average sound level must be adjusted to account for the fact, revealed by most community response and public opinion surveys, that the same noise environment is considered more disturbing or annoying during the night than during the day. Not only do the requirements for undisturbed sleep and relaxation make a lower nighttime noise level desirable, but the exterior background noise level in most communities drops during the night by 10 dB or more, and reduced activity inside homes contributes to a general lowering of interior noise levels. Consequently, intrusive noises are more disturbing during the night. To assess nighttime noise events in a way that accounts for their increased potential for causing disturbance, a weighting factor of 10 dB is applied to all nighttime noises: i.e., nighttime noises are treated as if they were 10 dB noisier than they actually are. The 24 h average sound level with a 10 dB nighttime penalty applied is called the day-night average sound level, Ldn, given by the expression Ld” = 10 log,, [E(lo=“““) +&(lo(L~+lo)‘lO)],

(1)

where Ld and L, denote the daytime and nighttimet average sound levels, respectively. In the full report Schultz goes on to discuss several possible disadvantages of the Ldn descriptor [l]. These potential disadvantages are as follows: (a) the effect of pure tones in the noise is not accounted for; (b) some other weighting may be preferable to A-weighting; (c) rare loud events may not be adequately accounted for; (d) there is some question about the nighttime penalty used in calculating the day-night sound level; (e) the factor of 10 multiplying the logarithm may be questioned. In the full report, each of these objections is discussed separately. In general, it is concluded that no other commonly used descriptor does a better job of accounting for the above objections, and that the complexities involved in trying to account for these objections are not justified by the claim that better correlation with annoyance could be achieved. In the second chapter of the full rating criteria report previous studies that have been made to determine the impact of railway noise on the community are reviewed. These studies included not only noise measurements but also results of interviews or questionnaires submitted to residents in the neighborhoods of rail lines to determine their annoyance. The subjective response to railway noise is compared with that due to road traffic and aircraft noise and is found to be nearly the same. The method usually used to develop a rating of acceptability for noise from a specific source is to combine the results of a large scale social survey with those from a +The

daytime

period

is from 0700 to 2200 hours;

the nighttime

period

is from 2200 to 0700 hours.

252

L. E. WITTIC

corresponding program of outdoor noise measurements. Both surveys are carried out in areas strongly impacted by the noise source in question. Comparison of these results permits one to determine what aspects of the noise are most important in generating annoyance, and then to develop a rating that combines assessments of the relative severity of these various aspects, to be used as a tool for evaluating different degrees of exposure to this noise. Unfortunately, at the time of this study no surveys had been completed that deal with the noise of rapid transit at all, either with track on grade or on elevated structures. Thus, it was necessary to rely on the results of several social surveys dealing with railroad noise, as representing the most nearly similar situation. In the recent past, the results of four studies dealing explicitly with rail noise and combining social surveys with noise measurements have been published: two in Britain, and one each in France and Japan [5-111. Although the first British survey was little more than a pilot study, never carried to completion, the other three present valuable data. Indeed, a portion of the Japanese survey concerns the New Sanyo Line of Shinkansen, for which most of the track is carried on elevated concrete structure. However, the Japanese results cannot be relied on for decisions about community response to noise in American communities, because of the great cultural and architectural differences between Japan and the U.S.A. Both the second British study and thl: French study showed that annoyance correlated better with the L,,noise scale than any other parameter. A comparison of the two studies is presented in Figure 2 under the assumption that Ldn= Leqcz4) + 4 (which corresponds to about 17% of the daily traffic at night). The top three steps out of seven in the French survey were counted as “highly annoyed”, because no other count is possible from the published data. According to the arguments presented in reference [12], a more consistent reckoning of high annoyance in the British survey would be to count the mean of the responses in (1) the top two and (2) only the top step. This would lower the curve for Question llb considerably, and would decrease the apparent agreement between the

80

70

20

IO

0 40

45

50

55

60 L,

65

70

75

80

85

(dB)

Figure 2. Comparison of “percent highly annoyed” for French and British railway noise surveys. The shaded area represents the range covered by the average response curves from 11 surveys dealing with transportation noise.

RAILWAY

ELEVATED

STRUCTURE

NOISE

253

French and British studies. The reason for this disagreement between British and French railroad surveys is not known. It may become clearer in subsequent analysis of the British survey data. The data from the recent surveys on railroad noise permit preliminary comparisons of community response to transportation noise of different kinds. The results of the French railroad noise survey do not suggest a different community response to railroad noise than to road and aircraft noise, as shown by the shaded area in Figure 2. Indeed, this railroad noise survey “clusters” very well with other transportation noise surveys including both aircraft and traffic noise. A best-fit empirical power function to these data is given by the following expression: (1.24 x 10-4)[100”03Ldn] %HA = (0.2)[10°‘03Ld-]+(l.43 x 10-4)[100’08L”~]’

(2)

A weighting function that can be used for assessing noise impact is obtained by normalizing this expression to unity at Ldn - 75 dB. The value at an Ldn of 75 dB is chosen to normalize the curve because it is the value selected by the U.S. Environmental Protection Agency (EPA) that was assigned full impact (allowing for an “adequate” margin of safety) [13]. The effect of this normalization is to change the coefficient in the above equation from (1.24 x 10p4) to (3.364 x 10d6). The resulting weighting function is given the symbol W(Ldn). The recommended procedure for determining noise impact from an elevated structure, or other transportation noise sources, for that matter, is to compute the Level Weighted Population (L WP) using the expression LWP=

IA

W(Ldn)D a,

(3)

where w(L&,) is the weighting function explained above, D is the population density, and A is the area under consideration. In reality the above integral would probably be replaced by a summation. For example, one might draw on a map Ld,, noise contours at 5 dB increments; determine the number of people between each set of contours; weight them, respectively, by the value of w(Ld,) for average value of the bounding contours; and perform the summation. 3. INVENTORY OF U.S. ELEVATED STRUCTURES The purpose of this task was to identify those structures in the U.S.A. that are responsible for the greatest environmental noise impact, and to quantify their impact in accordance with the methods discussed in the previous section. Subsequent to this task, the type of structure responsible for the greatest impact was selected for detailed analytical analysis and field measurements. The summary presented here is based on a separate report by Towers [ 141. The first step in this task was to obtain maps, descriptions of structure types, schedules, and other information from each of the U.S. rapid transit authorities. A summary of the structure types and their lengths is presented in Table 1. The MARTA (Metropolitan Atlanta Rapid Transit Authority), BART (Bay Area Rapid Transit District-San Francisco), PATCO (Port Authority Transit Corporation of Pennsylvania and New Jersey), and WMATA (Washington Metropolitan Area Transit Authority) systems are all relatively new, and their structures, which have solid concrete decks, are fairly quiet. The Dade County Metrorail (Miami area) is now under construction. Of the older systems,

Steel solid web girder Steel lattice web girder Steel solid web girder

Concrete girder Concrete girder

Steel girder Steel girder Steel girder Steel girder

CTA

Dade County Metrorail

MBTA

1

3.4 (2.1)

No fixation

Jointed

Direct

Open (wood ties)

lattice web

3.7 (2.3)

No Jointed fixation

Direct

Open (wood ties)

solid web

0.3 (0.2)

34 (21)

No

No

Welded

slab

Concrete

solid web

Welded

1.6 (1.0)

7.2 (4.5)

1.6 (1.0)

fasteners

Yes

Yes

43 (27)

No

slab

Concrete

solid web

Resilient

Welded

Jointed

No

No Jointed Jointed

32 (20)

No

Welded

Route distance km (mi) 1.3 (0.8) 0.9 (0.6) 0.6 (0.4)

Noise barrier Yes No Yes

Welded Welded Welded

Track type

Jointed

slab

Concrete

beam

fasteners

and wood

fixation

Resilient

Ballast ties

Direct

fixation

fasteners

Resilient Direct

fasteners fasteners fasteners

type

Resilient Resilient Resilient

Track support

classification

Ballast and wood ties Direct fixation

slab

Concrete

beam

(wood ties)

Open slab

(wood ties)

slab

Concrete

structure

Open

slab slab slab

Concrete Concrete Concrete

Deck type

Elevated

Concrete

box

Concrete girder

BART

type

Steel box girder Steel bbx girder Concrete box girder

Stringer

MARTA

Transit system

I

TABLE

U.S. urban rail transit system elevated structures

Concrete girder

Steel lattice web girder Steel lattice web girder Steel lattice web girder Concrete beam

PATCO

SEPTA

WMATA

Ballast ties Ballast ties

Concrete

slab

Concrete

Concrete slab

slab slab

Concrete Concrete

box girder

slab

Concrete

slab

(wood ties)

Concrete

Open

Steel/concrete composite Concrete slab

Concrete

Steel/concrete composite fasteners

and wood

and wood

fixation

fixation

fasteners

fasteners

Resilient fasteners Ballast and wood ties Resilient fasteners

Resilient

Resilient

Ballast and wood ties Ballast and wood ties Direct fixation

Resilient

Direct

Open (wood ties) slab

Direct

Open (wood ties)

Steel solid web girder Steel box girder Concrete box girder

beam

Steel solid web girder Steel lattice web direct Concrete beam girder Steel and concrete girder

NYCTA

1.3 (0.8) 1.4 (0.9) 3.9 (2.4) 8.5 (5.3)

Yes No No No

Jointed Jointed

Welded

Welded Welded

Welded

Welded

Jointed

Welded

Jointed

0.8 (O-5) 1.6 (1-O) 8.0 (5.0) 2.0 (1.2) 0.6 (0.4)

No No No No No

No

9.0 (5.6)

Jointed

No

92.4 (57.4) 0.5 (0.3)

No No

Jointed

Jointed

$ m

3 c $

E

2

z <

F 7

256

L. E. WIl-l-IG

the NYCTA (New York City Transit Authority), the MBTA (Massachusetts Bay Transportation Authority), and the CTA (Chicago Transit Authority) are dominated by structures with open tie decks supported by steel girders. The girders for these structures are made of I-beams formed either by steel plates and angle irons or by a steel lattice. Also at the CTA, MBTA, and SEPTA (Southeastern Pennsylvania Transportation Authority-Philadelphia) are structures whose track support consists of tie and ballast on a concrete deck supported in turn by either solid web steel girders or steel lattice web girders. Field or llteroture

do+a

4 Amblent L,

Figure

3. Flow chart of noise impact

assessment

methodology

for elevated

transit

structures.

Figure 3 presents a flow chart of the procedure used to assess the impact from each type of structure. When possible, the noise level of a given structure was determined from the published literature and reduced to Single Event Noise Exposure Level (SENZX)? for a single train. When sufficient data were not available, field measurements were conducted. In this study, field measurements were made in Boston, New York, and Chicago. The average noise level of several train passages was again reduced to the SENEL. The SENEL was then coupled with schedule information to determine the Ldn as follows: Ld”(d) = SENEL(d) + log (Nday+ lONni&t)-49*4,

(4)

where Ld,(d) is the day-night average sound level, in dB, at a distance d; SENEL(d) is the single event noise exposure level, in dB(A), for a typical train passby at the same distance d ; Nday is the number of train passbys between 0700 and 2200 hours; and Nnight is the number of train passbys between 2200 and 0700 hours. Next the impact zone was determined by considering only those locations where the elevated structure noise raised the ambient noise by more than 1 dB (that is the zone where the structure noise was greater than the ambient noise minus 5 dB). The ambient noise was determined by field measurements or by using the correlation that the EPA has developed between Ldn and population density. Finally, the above information was coupled with population data, and the procedure explained in section 2 was used to calculate the L WP. The Dade County Metrorail figures are based on environmental predictions for that system. In New York, Chicago, and Philadelphia, the population was estimated from actual physical inventories. For the other cities, more general population density information was used. In performing the LWP calculations it was necessary to account for the reduction in noise level with t The SENEL is defined as the sound level of a signal with a duration of one second that contains the same acoustic energy as the time-integrated sound level of a single train passby. SENEL, which is expressed in dB(A),

provides

a measure

that accounts

for both the duration

and the level of a single noise event.

RAILWAY

ELEVATED

STRUCTURE

NOISE

257

distance, as well as any shielding effects. In locations where rows of buildings faced the structure, only the residents on the side of the building facing the track were counted. It was assumed that the closest buildings provided enough shielding to protect those on the back side of the buildings and those in subsequent rows of buildings further from the tracks. A detailed summary of the results is presented in Table 2. The noisiest structures are seen to be the open-deck (wood-tie) steel variety; girder design (i.e., solid- us. lattice-web) does not seem to be a significant factor relating to noise from these structures, according to the above results. Structures with concrete or concrete/steel composite decks, ballasted track, and jointed rail are seen to be less noisy than the open deck steel structures; this may be due to the combined effects of ballast absorption and the reduction of structural radiation. Structures with concrete deck, resilient fasteners, and welded rail make up the least noisy group of structures. These structures show a wide variation in noise levels, suggesting that factors other than structural characteristics may be strongly influencing noise emission. For example, results for the PATCO and SEPTA structures in this category reveal L,,, values of 90-91 dB(A), significantly above the 76-85 dB(A) range encountered for similar structures in newer transit systems. These higher values may result from the predominance of noise generated by vehicle components (e.g., propulsion system, wheels, etc.) for the transit cars used on the PATCO and SEPTA systems. Note that structures with noise barriers are not included in the present discussion, since barrier effects are site-specific. The non-structure data indicate that train operations on elevated structures are 1-16 dB noisier than operations at grade on ballasted track for similar vehicle and rail conditions. This increase may be due to a combination of factors, such as reduction of ground absorption, loss of undercar ballast absorption, and noise radiation from structure components. Table 2 provides residential noise impact information for each elevated structure type in terms of impacted population? (P) and Sound Level Weighted Population (LWP). The results estimate that approximately 384 300 people in the U.S.A. are exposed to noise from rail transit operations on elevated structures. The total L WP is estimated to be about 646 000, which implies that the impacted population of 384 000 is exposed to an average Ldn of 82.5 dB. In fact, Table 2 indicates that about 40% of the total impacted population is exposed to transit noise within the 80-85 dB Ldn range. Another interpretation of the L WP is that the nationwide noise impact from elevated structures is the same as if about 646 000 people were 100% impacted. The results shown in Table 2 lead to a rank-ordering of structure types according to noise impact. The following five structures account for 99% of all U.S. elevated structure noise impact: (1) steel solid-web girder, open deck (wood-tie), jointed rail: LWP = 574 886; (2) steel lattice-web girder, concrete deck, ballast-and-wood-tie, jointed rail: L WP = 22 122; (3) concrete beam girder, concrete deck, ballast-and-wood-tie, jointed rail: LWP = 18 697; (4) steel lattice-web girder, open deck (wood-tie), jointed rail: L WP = 10 757; (5) steel lattice-web girder, concrete and steel deck, ballast-and-wood-tie, jointed rail: L WP = 10 087. These results indicate that steel structures with solid-web girders, open deck (wood-tie), and jointed rail are responsible for the greatest noise impact by far, accounting for 89% of the total nationwide L WP. The approximately 139 km (87miles) of this structure, which are located primarily in New York and Chicago, make up more than half of all U.S. elevated structures. t Defined

here as the number

of people

within the impact

zone

r

type

Total structure

X

X

TM--

X

X X

X

X

X

X X

X

X

X

Track type

X

X

X

Track support type

classification

X

X

Deck type

rapid transit structure

Total structure

Stringer

Elevated

2

X

X

X

X

X

X

\ (es No

Noise Barrier

MBTA CTA MBTA WMATA CT-A MBTA NYCTA SEPTA

CTA MBTA NYCTA

Transit system

(86.7) (0.2) (1) (1) (1) (4.5) (2.1) (0.3) (0.3) 11.5 (7.2)

139.1 0.3 1.6 1.6 1.6 7.2 3.4 0.5 0.4

43 (27) 3.7 (2.3) 92.4 (57.4)

Route distance km (mi)

97 90 99 77 103 107 101 -

100 104 106

Z[7] 98 [81 90 [91 -

91[71 98 [81

88[81

91 PI 98 [81 90 [91

Estimated noise levelt L,,, at 7.5 m (25 ft) 60 km/h (38 miles/h), dB(A) , I Structure Non-structure

U.S. elevated rail transit structure noise impact inventory summary

TABLE

119 786 855 454 245 574 886 30 244 125 0 9504 310 943 0 10757

298 722 60 364 296 0 5672 412 711 0 6795

’ Sound level weighted population (LW.) 71852 1302 225 568

Impacted population (P)

I

Residential noise impact

P g

r

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

X

NYCTA

WMATA

WMATA MARTA BART

NYCTA Dade Metrorail Dade Metrorail PATCO SEPTA

SEPTA SEPTA MARTA MARTA WMATA

(5.3) (2.4) (0.8) (0.6) (5)

(11.9) (1.2) (0.4, (20)

report

32.6 (20.4) 1.3 (0.8) 260 (162)

0.6 (0.4)

19.2 2.0 0.6 32

17 (10.5) 1.4 (0.9) 0.8 (0.5)

8.9 (5.6) 9.0 (5.6) 17 (10.5)

8.5 3.9 1.3 0.9 8.0

t Unless otherwise referenced, the L,,, values are estimated from data presented on the appropriate 2. Values in parentheses refer to references for measured data not discussed in the Appendices.

structure

Total structure

X

X

Total structure

X

X

Total structure

X X

X

X

X

X

X

X

X

X

X

X

Total U.S. elevated

X

X

Appendix,

90

77

151

90 E91

;I?. -

-

75 83 [ll] -

75

90 [91

-

using the adjustment

77 76 85 [12]

80 90 [ll] 91 [lo]

95 70

96 [lo] 96 [lo] 76 85 77

techniques

17712 3114 384 293

0

4263 0 30 17712

2891 392 980

33 23229 2891

16752 10018 14 33 0

presented

in section

4603 2349 646036

n

g E

: e” g

Y

6

5 0

$ 4603

B

1

$ $

1603 0 3

525 147 931

4 18697 525

1 4 0

22122 10087

260

L. E. WITTIG

The five structures listed above are included among the two noisiest structure categories described earlier. The least noisy structures, which use welded rail mounted on concrete deck with resilient fasteners, account for approximately 70 km (50 miles) or almost one-third of all U.S. elevated structures. These structures, however, are found primarily in newer transit systems and account for only 1% of the total noise impact from U.S. elevated rail transit structures. Figure 4 presents a pie graph summary of these results. On the basis of the results of this task, only the open-tie-deck, solid-web girder structure was chosen for the analytical modeling task described in the next section.

Route

dbstance

Figure 4. Noise impact

concrete /steel structure, SOhd deck, res,,,ent trOCkfasteners,weldedrc,,

inventory

4. ANALYTICAL

of U.S. rail transit

Nose Impact

elevated

structures.

MODEL ANALYSIS

4.1, OVERVIEW OF THE ANALYTICAL MODEL TASK The purpose of the task described in this section was to develop an elevated structure analytical model for assessing the noise reduction achievable through a variety of noise control treatments. The model could then be used as a tool to help in the development of cost-effective treatments to reduce the noise impact at the residential locations adjacent to these structures. The work described here focuses on the open-tie-deck, solid-web girder structure that dominated the impact survey discussed in section 3. This description is only a brief summary of a more complete Department of Transportation report by Remington, Wittig and Bronsdon [16]. A block diagram of the analytical model is shown in Figure 5 along with a drawing of the elevated structure identifying its components. The analysis has been broken into three parts: the generation of wheel and rail vibration during the passage of a train, the transmission of vibration from the rail to other structural elements, e.g., ties and girders, and the radiation of sound to wayside from the wheels, rails, ties, and girders. The calculation of the generation of wheel and rail vibration is based on work by Remington, Rudd and Ver [17]. The transmission of vibration from the rail to the various components of the structure has been calculated by using Statistical Energy Analysis techniques. As Figure 5 shows, the structure is composed of two rails resting on tie plates which, in turn, are usually separated from the wooden ties by a $in thick asphalt “tie-saver” pad. The ties rest on two girders that are built up of steel plates and angles riveted or welded together to form I-beams composed of a web, flanges, and web stiffeners, as shown in the figure. There are usually small metal brackets that clamp the

RAILWAY Wheel and rail response

ELEVATED

STRUCTURE

Transmission through structure -

the

NOISE

261

Sound radiation

Tie plate

Figure 5. Analytical model methodology and nomenclature for open-tie deck, steel web girder structure.

ties (usually only every other tie or every third tie) to the girder flange. Steel angle beams interconnect the two girders as shown in the figure. The response of the ties and girder webs, believed to be the primary radiating component of the structure, has been calculated in terms of the rail vibration. The approach taken follows the lead originally proposed by Manning et al. [18] in that the rail vibration is assumed to consist of a distribution of traveling waves. The resulting flow of power is, however, quite different from that in Manning’s work. The generation of sound by the wheels, rails, ties, and girders has been calculated using the sound radiation properties of these components measured by Remington, Rudd and Ver [17] and Manning et al. [18]. During the passage of a train, the rail vibration along the rail beneath the train is highly irregular. Consequently, it was necessary to deal with the average levels during a train passage. The resulting predicted sound levels at the wayside are average sound levels in which it has been assumed that the averaging time was sufficiently long to obtain all the sound energy in the passby. To verify the analytical model, an extensive series of measurements was carried out on the 10th Ave elevated line of the NYCTA at 210th St. in Manhattan. Noise and vibration measurements were performed on this structure both before and after installation of resilient fasteners between the rails and the ties. The resilient fasteners were installed to reduce the noise radiated by the structure and, consequently, provided the program with a unique opportunity to test the predictive capabilities of our model in assessing the benefits of that noise control treatment on elevated structure noise. In addition to the field measurements, we also carried out a number of laboratory measurements to define better a number of the parameters required in the analytical

262

L. E. WITTIG

model. These measurements included the dynamic stiffness and loss factor of the resilient fasteners mentioned above, the static stiffness of these fasteners, the static stiffness of the “tie-saver” pad, the local static stiffness of the ties, and the damping loss factor of the ties. 4.2.

WHEEL/RAIL

INTERACTION

As the wheel rolls along the rail, small-scale roughness and discontinuities (wheel flats and rail joints) on the running surface of the wheel and rail act to excite vibration in both. The vibrating rail then excites the remainder of the structure and, in turn, the wheel, rail, and components of the elevated structure all radiate sound. In this section the interaction and resulting response of the wheel and rail are examined. In later sections the transmission of vibration through the structure and the resulting radiation of sound are considered. The response of the wheel and the rail to the small-scale roughness on their running surfaces has been examined in some detail by Remington [19] (see also references [20-221). He has shown that the spectral density of the rail and the wheel are given by

(5) l ,““’ 1,“”R~21H,,(k)liS.,“~~o. sR(w)=zk vT7jR z +z The average wheel vibration velocity spectrum is given by

where &(w) and SW(w) are the average rail and wheel velocity squared in bandwidth on frequency w, Zw and ZR are the wheel and rail point impedances, respectively, V is the train speed, &(k) is the filtering of the rail roughness produced by the finite area of contact between the wheel and rail, k is w/V, S,,,~(k) is the sum of the spectral densities of the roughness on the wheel and rail, N is the number of wheelsets on the train, and T is the averaging time. on the rail, is given by kR = The value of kR, the wavenumber 2 1’ 4, where w. is the natural frequency of the rail when modeled wmcd1’2[1 -two/w) 1 as a beam on an elastic foundation. VR is the spatial loss factor of the rail: that is, the rail vibration is assumed to drop off as e-‘lnkRX,where x is the distance from the point of excitation. Aw centered

4.3. VIBRATION TRANSMISSION In this section, the coupling between rail vibration and the vibration of other components of the elevated structure is examined. In particular, the focus is on two components-the tie deck and girder web-that are likely to make significant contributions to the sound radiation from the structure. A Statistical Energy Analysis (SEA) approach is taken to the estimation of the coupling. SEA has a number of advantages. Of primary interest here is that a very complex dynamic interaction problem is reduced to a solution of a set of linear algebraic equations. Despite the reduction in complexity, the resulting solutions still are capable of predicting the effects of many of the noise control treatments that one would consider applying to elevated structures such as resilient rail fasteners or increased girder damping. Because of the complexity of the detailed SEA model and limitations on space, the discussion here is limited to an overview of this model. Those interested in a more detailed explanation are referred to the complete DOT report [ 161.

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263

In order to simplify the analysis of the transmission of vibration through the elevated structure, the motion of the rail is assumed to be solely vertical motion in bending and composed of pure traveling waves of the form ekWt-@). Of course, as already discussed in section 4.2, the vibration does decay along the rail. If, however, that decay rate is not too rapid, then the results of this analysis should be essentially correct. The analysis of the interactions within the structure is broken into two parts: rail-tie interaction and tie-girder interaction.

Tie local

stiffness Glrderflange bendmg Impedance

Tie

bendlng

Impedance

Girder web compresslo” end shear stiffness

Figure

6. Rail-tie

interaction.

Figure 6 shows schematically the rail-tie interaction. The dynamic motion of the rail compresses and extends the supporting rail fastener or “tie-saver” pad. The tie deforms locally in compression under the fastener and also deforms in bending. As will be seen later, it is the tie bending deformation that is of primary interest in transmitting vibration to the girder web. The tie bending deformation is resisted by the supporting girder, which acts through the local stiffness of the tie from underneath. The girder impedance that resists the tie bending deformation is modeled as a beam having the bending properties of the flange supported on the compressional and shear stiffness of the girder web. The relative magnitudes of the impedances of these elements in the elevated structure, shown in Figure 7, are based on estimates derived using the parameters of the NYCTA 10th Ave elevated structure. It should be emphasized that the impedances shown in Figure 7 are not point impedances but would be more properly called “traveling wave impedances”. For example, if one of the components of the structure, such as the girder, were excited by a traveling wave force such as might arise from the motion of the rail, the traveling wave impedance predicts the amplitude and phase of the traveling wave response velocity on the component where the force is applied. Figure 7 shows that the impedance of the girder in bending in the vertical plane (which goes off the top of the graph) is much greater than any of the other impedances, and, consequently, girder bending deflections can be ignored. The impedance for another possible mode of deformation of the girder is also shown in the figure. In this mode, the flange deforms in bending resisted by shear deformation of the girder web. The impedance of the girder web in shear is spring-like, and the flange resting on the web is similar to a beam on an elastic foundation. The rapid fall in the girder impedance at high frequency is due to a wave coincidence effect in which the wave speeds in the rail match the wave speeds in the flange on the girder web stiffness.

264

L. E. WITTIG I \

Girder bendlng impedance

blocked

Impedance

IK,/Jw) 100

Ik Frequency

IOk (Hz1

Figure 7. Comparison of the estimated impedances of the components of the elevated structure.

The “tie-saver” pad and the local deformation of the tie are assumed to have spring-like impedances with the spring constants determined from static tests. The impedance of the resilient fastener is derived from both measurements on and analytical estimates of the dynamic stiffness of the fasteners installed on the NYCTA 10th Ave elevated structure. The estimate shown includes the effects of thickness resonances in the fastener and assumes that the fastener is a 70 durometer pad at 70°F resting on a rigid foundation. In fact, at high frequency, the ties do not provide a rigid foundation; consequently, the estimate shown is probably in error in the l-2 kHz range. The thickness resonances were not expected but are a consequence of the very low propagating wave speeds in the rubber material of the fastener. These low wave speeds allow propagating waves generated at the rail foot to exist in the rubber, reflect off the base plate of the fastener, and return to the rail foot either in phase (resonance) or out of phase (antiresonance) with the rail foot motion. The result is an impedance that is markedly different from the commonly assumed “lossy” spring. The picture that emerges of the rail-tie-deck interaction is a rather complicated one. At very low frequency, the tie deck bending impedance is quite low, and the deck goes along for the ride, driven by the rail fastener through the local tie stiffness. The girder, with a very high impedance is essentially rigid underneath the tie, and deformation of the tie locally is more important than the girder deformation. At the mid frequencies, all impedances except the girder are of comparable magnitude, and the interaction is fairly complicated. The girder appears to enter the interaction with the tie only at high frequencies where the girder impedance drops rapidly for reasons described earlier. The rail causes the tie deck to vibrate in bending. These bending vibrations then couple to bending vibration in the girder web. The coupling at the tie-girder interface is through both rotation and lateral translation of the top of the girder web. The lateral translation, illustrated in Figure 8, is a consequence of the finite thickness of the ties and is the major component in the coupling at higher frequencies.

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Figure 8. Tie-girder interaction (exaggerated). (a) Undeformed bending.

NOISE

265

tie and girder; (b) tie-girder interaction in

4.4. SOUND GENERATION

In this analysis, we have picked the average sound pressure level at a wayside location to describe the noise environment of a passing train on an elevated transit structure. The average sound level is defined as the total sound energy generated by a train passage divided by a specified time period T. This period is generally greater than the time period for which the sound pressure level is 10 dB or more down from its peak value. The rail, tie deck, and girders were treated as passing finite length line sources, and the average sound energy (ASE) they radiate was found to be given by (7) where u is the radiation efficiency, h is the height of the item (or the characteristic size used in determining the radiation efficiency), pc is the acoustic impedance, (u2(t)) is the mean square velocity of the vibrating element, and d is the distance to the point of observation. The average sound energy radiated by all sources is given by the above equation, plus a factor of two (i.e., 3 dB) for ground effects, and an additional factor of two for the rails and girders because there are two of each of these sources. Directivity was not taken into account. Generally, it was assumed that the sound energy from all of the sources radiates into the non-absorptive irregular space under the car, and then spills out to the sides and bottom. The fact that the car may block some of the energy from radiating directly upward, and thus increase the energy radiating to the sides, was considered secondary and therefore ignored. The value of u for the rails is based on an empirical curve fit to the theoretical value given by Manning [18]. This expression is ~RAIJ_(~)= l/11 + (Wcrit/W)3},

(8)

where Wcrit= 2?rfcdtis the critical or coincidence frequency of the rail. For the data presented by Manning, the best curve fit was obtained with fcrit= wCti,/2rr = 630 Hz. The radiating area used for the rail is twice the combined width of the foot and the head times the unit length of the rail.

266

L. E. WI’ITIG

The value of u for the ties is also given by equation (8), except that fcrit = w,-,it/2v should be 500 Hz. The radiating area per unit length is the sum of the top and bottom areas of the tie divided by the tie spacing. The radiation efficiency that we used for the girder was based on a curve fit to the value given by Manning [18, Figure 3.271. In this case, we fitted a curve to the theoretical prediction that took into account short circuiting around the girder flanges. Manning’s field data were 4-5 dB greater than this theoretical curve; we think this may be due in part to a ground reflection. Since we are accounting for the ground reflection separately, we fitted our curve to the theoretical curve rather than the field data points. Our expression for the radiation efficiency is (+GIRDER

=

l/I1

+

(Wcrihgo/Whg)“‘}*

(9)

In this case, the factor &J/r,), where h, is the girder thickness, has been included to allow the critical frequency to change if the thickness of the girder changes. The baseline value of f,-ri, is 1000 Hz, and the corresponding baseline thickness h,, is 0.5 in. The radiating area includes both sides of the girder. The concept of sound power radiated per unit length is not valid for the wheels; however, it is fairly straightforward to calculate the sound energy that is radiated from the wheels. The mean square sound pressure from both sides of a single wheel, at a distance d from the track and a distance x along the track, is given by (p2) =cr(pc)2Aw(u2,>/4~(d2+x2),

W)

where A, is the area of one side of the wheel, and is the mean square vibration velocity of the wheel. The radiation efficiency term accounts for radiation from both sides of the wheel. The average sound energy is found by letting x = Vt, integrating the above expression with respect to t from --OOto +oo, and dividing the averaging time T. This gives (ASE)WHEELS=~A~(PC)~(~Z~)/~~VT.

(11)

The total wayside average sound level depends on the number of wheels that pass in the time T, as well as ground effects. The value used for the radiation efficiency was based on theoretical calculations and measurements reported by Remington [17]. These data were normalized by the area of one side of the wheel, but since the wheel radiates off both sides, the value of u is equal to 2 for all frequencies above 200 Hz. The expression used in our calculations is CWHEELS

with foi, = o,,.J~I~ = 110 HZ.

=

2/{1

+

(Wcrit/o)2}

(12)

OF MODEL PREDICTIONS WITH FIELD MEASUREMENTS 4.5. COMPARISON In order to develop some confidence in the analytical model of the open-tie-deck elevated structure described in the preceding sections, we have compared model predictions to data measured on the 10th Ave elevated structure at 210th St. on the NYCTA [23]). As described earlier, this structure presented us with a unique opportunity. We were able to make noise and vibration measurements on this structure before and after installation of resilient rail fasteners over approximately 1000 ft of the structure. Since we are able to compare analytical model predictions with measurements on the structure in two different configurations, the validity of our model will be well tested.

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125

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I

I

I

I

250

500

Ik

Zk

Frequency

267

1 41

(Hz)

Figure 9. Average A-weighted sound level at 25 ft during the passby of a 10 car train at 22 miles/h on the NYCTA 10th Ave elevated with tie saver pads. -, Overall (94.5 dB(A)); - -, tie deck (91 dB(A)); - - -, girder (87.5 dB(A)); ---, rail (89 dB(A)); ----, wheel (80dB(A)); 0, measured data (93.5 dB(A)); T = 32 s; V = 22 mph; 10 car revenue service train; tie saver pads: no = 0.02.

Figure 9 shows a comparison of predicted and measured sound levels in one-third octave bands. Figure 10 compares measured and predicted overall sound level for a range of speeds and, again, the agreement is quite good. The predictions presented in Figures 9 and 10 are for an estimated girder loss factor of 0.02. Subsequent measurements for the NYCTA study showed this value to be approximately 0.004.

I

I

_HQG /-_-

_

0 /_/ ,_--I_---___c:_---

-;_-

.?-. 6

_----

IO

_ .

A

20 Speed

_-’

_-y

30

40

(m&s/h)

Figure 10. Average A-weighted sound level during the passby of 10 car train on the NYCTA 10th Ave elevated with tie saver pads. -, Overall; - -, tie deck; - - -, rail; - - -, girder; - - - -, wheel; 0, measured data; T = 32 s; 10 car revenue service train; tie saver pads; no = 0.02.

Figure 11 compares measured and predicted A-weighted one-third octave band sound levels during a train passage after the structure had been fitted with resilient rail fasteners. Note that these predicted levels were also performed for a girder loss factor of 0.02. The measured and predicted overall A-weighted sound levels us. speed are compared in Figure 12. The predictions agree well with measured data except for one point at

268

L. E. WIT-I-IG

4

40

I 125

I

I

250

500

Frequency

I Ik

I 2k

4k

(Hz)

Figure 11. Average A-weighted sound level during the passage of a 10 car train at 10 mph on the NYCTA 10th Ave elevated, assumed to have 50 durometer resilient fasteners. -, Overall (81 dB(A)); --, tie deck (75 dB(A)); - - -, girder (72 dB(A)); -- -, rail (77 dB(A)); - - - -, wheel (72 dB(A)); 0, measured data (81 dB(A)); T = 32 s; V = 10 miles/h; 10 car revenue service train; 50 durometer resilient fastener; no = 0.02.

31.5 miles/h. It is believed that propulsion system noise, which is a significant source at that speed on the NYCTA, may have contributed to the discrepancy. Comparing Figures 10 and 12, one can see that the presence of the resilient fastener has reduced the noise from the structure at the lower speeds by about 5 dB(A). Noise from the propulsion system may have prevented a similar reduction at the higher speeds, The noise reduction is a consequence of a reduction in rail sound radiation of about 4 dB(A) and a reduction of tie deck and girder sound radiation of about 8 dB(A). Rail sound radiation decreases because of a reduction in rail vibration brought about through the damping introduced by the rail fastener. The tie deck and girder sound radiation decreases because of a decrease in their vibration brought about by the decreased rail vibration, by the additional isolation introduced by the fastener, and by the damping introduced into the tie by the rail fastener.

I 30

I 20

Speed

I

I

40

50

(miles/h)

Figure 12. Average A-weighted sound level during the passage of a 10 car train on the NYCTA 10th Ave Overall; - -, tie deck; - - -, rail; - - -, girder; elevated, assumed to have 50 durometer rubber pads. -, ---, wheel; 0, measured data resilient fastener; 0, measured data tie saver pad; T = 32 s; 10 car revenue service train; 50 durometer resilient fasteners; no = 0.02.

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269

5. CONCLUSIONS The following general conclusions can be drawn from the study described in this paper. 1. The loudness of a train passby, either on an elevated structure or at-grade, should be measured in terms of the maximum A-weighted sound level. This scale should also be used to judge the effectiveness of noise control treatments. 2. The annoyance caused by noise from trains correlates well with the measured noise expressed in terms of the Ldn descriptor. The level of annoyance for train noise at a given Ldn is the same as it is for other transportation noise sources at the same Ldn. 3. The best way to rank order the environmental noise impact from elevated structures is in terms of the Level Weighted Population (L WP). 4. More than 280 000 people in the U.S.A. are exposed to Ldn levels in excess of 80 dB at the facades of the buildings in which they live. The open-tie-deck, solid-steel-web girder structure accounts for approximately 50% of the total miles of elevated structures and 90% of the impact. The newest structures in the U.S.A., which use welded rail mounted on concrete decks with resilient fasteners, account for approximately one-third of the route miles but only 1% of the total impact. 5. A statistical energy analysis model has been developed for the open-tie-deck, solid-steel-web girder structure that can be used to study the noise reduction effectiveness of certain treatments such as resilient rail fasteners and girder damping. 6. Measurement results combined with the results from the analytical model show that the dominant sources of noise from the open-tie-deck, solid-steel-web girder structure are, in order of importance: the wood tie deck, the girders, the rail, and the wheels. This was a somewhat unexpected result; it follows that damping the girders in the absence of other noise control treatments would not result in a significant reduction of noise. 7. Although not a major aspect of this study, it was determined that the noise from the propulsion motors on transit cars can equal or exceed the other noise sources at high speeds. 8. The retrofit of the NYCTA elevated structure with resilient fasteners was found to reduce the wayside noise by 3-5 dB. The mechanism primarily responsible for the decrease in noise was the damping of the rail provided by this fastener, rather than any isolation that it might have provided. The stiffness of the fastener was approximately equal to the local stiffness of the tie. 9. The analysis of published data (not discussed in this paper) showed that careful attention must be paid to the type of structure being treated. A noise control treatment that works well on one type of structure may not provide a significant amount of noise reduction on another. A number of potential noise control treatments were reviewed, and a table was presented that listed the most effective treatment for each type of structure. 10. The noise reduction effectiveness of barriers and damping on the solid concretedeck steel box-beam Atlanta structure was measured but not discussed in this paper. The barriers were found to provide a wayside noise of approximately 9 dB, while damping the steel box beam lowered the wayside noise level by approximately 1 dB. ACKNOWLEDGMENTS This paper presents the results of a study conducted by Bolt Beranek and Newman Inc. (BBN) under contract to Urban Mass Transportation Administration, U.S. Department of Transportation (DOT). Technical direction was provided by the Transportation Systems Center, a research branch of DOT. Doctors Leonard Kurzweil and Robert Kendig served as technical co-ordinators, and were later succeeded by Michael Dinning and Robert Hickiey.

270

L. E. WImIG

The measurements made on elevated structures of the New York City Transit Authority (NYCTA) and of the Metropolitan Atlanta Rapid Transit Authority (MARTA) were carried out with the co-operation, respectively, of the Environmental Staff Division of NYCTA, under the direction of Mr Anthony Paolillo, and of the engineering staff of MARTA, under direction of Mr Morris Solomon. Their participation and assistance are greatly appreciated. Amman & Whitney, Consulting Engineers, under subcontract to BBN, assisted in this study in the collection of physical data for the noise impact survey and in the conceptual design and feasibility analysis of noise control treatments; Mr Samuel Weissman directed the Amman & Whitney tasks. An advisory board that was made up of representatives from each of the transit systems in the U.S.A. participated in supplying information needed for the survey and by reviewing the progress of the study at various stages. This effort was co-ordinated Gordon of the American Public Transit Association.

by Mr Theodore

REFERENCES

1. T. J. SCHULTZ 1979 U.S. Department of Transportation, ReportNo. UMTA-MA-06-0099-793. Noise rating critera for elevated rapid transit structures. 2. T. J. SCHULTZ 1974 U.S. Department of Transportation, ReportNo. UMTA-MA-06-0025-742. Development of an acoustic rating scale for assessing annoyance caused by wheel/rail noise in urban mass transit. 3. T. J. SCHULTZ 1972 Community Noise Ratings, Applied Acoustics Supplement No. 1. Barking, Essex: Applied Science Publishers Limited. 4. K. S. PEARSONS and R. L. BENNE-I-I’ 1974 NASA Report CR-2376. Handbook of noise ratings. 5. D. WALTERS 1968 Research Report 2, Birmingham School of Architecture, Birmingham, England. Railroad noise in housing areas. 6. D. E. BISHOP 1973 Bolt Beranek and Newman Inc. Report No. 2424. Program for the measurement of environmental noise. Appendix B: review of previous surveys by T. J. Schultz. 7. D. WALTERS 1969 Architectural Psychology : Proceedings of the Conference held at Dalandhui, University of Strathclyde. Annoyance due to railway noise in residential areas. 8. J. M. FIELDS and J. G. WALKER 1978 Third International Congress on Noise as a Public Health Problem, Freiburg, Germany. Comparing reactions to transportation noises from different surveys: a railroad noise us. aircraft and road traffic comparison. Railway noise and vibration 9. J. M. FIELDS 1979 Journal of Sound and Vibration 66,445-458. annoyance in residential areas. 10. D. AUBREE 1973 Centre Scientifique et Technique du Bdtiment, Paris. Acoustical and sociological survey to define a scale of annoyance felt by people in their homes due to the noise of railroad trains. (Translation available from BBN as 1973 Technical Information Report No. 88.) 11. T. SONE, K. SHUNICHI, N. TADAHOTO, K. SHUNICHI and K. MASAZUMI 1973 Journal of the Acoustical Society of Japan 29, 214-224. Effect of high-speed train noise on the community along a railway. (Translation available from BBN as 1973 Technical Information Report No. 87.) 12. T. J. SCHULTZ 1978 Journal of the Acoustical Society of America 64, 377-405. Synthesis of social surveys on noise annoyance. 13. U.S. Environmental Protection Agency, Office of Noise Abatement and Control 1974 Report No. 550/g-74-004. Information on levels of environmental noise requisite to protect public

health and welfare with an adequate margin of safety. 14. D. A. TOWERS 1980 U.S. Department of Transportation, Report No. UMTA-MA-06-009980-5. Noise impact inventory of elevated structures in U.S. urban rail rapid transit systems. 15. Command 2056 1963 Noise : Final Report of the Committee on the Problem of Noise. London: Her Majesty’s Stationery Office. 16. P. J. REMINGTON, L. E. WING and R. L. BRONDSON 1980 Bolt Beranek and Newman Inc. Report No. 4347. Prediction of noise reduction in urban rail elevated structures. 17. P. J. REMINGTON, M. J. RUDD and I. VER 1975 U.S. Department of Transportation, Report No. CJMTA-MA-06-0025-7512. Noise prediction models for elevated rail transit structures.

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18. J. MANNING, D. HYLAND, J. FREDBERG and N. SENAPATI 1975 U.S. Department of Transportation, Report No. UMTA-MA- 06- 0025- 75- 12. Noise prediction models for elevated rail transit structures. 19. P. J. REMINGTON 1976 Journal ofSound and Vibration 46,419-436. Wheel/rail noise, Part IV: Rolling noise. 20. P. J. REMINGTON 1976 Journal of Sound and Vibration 46, 359-379. Wheel/rail noise, Part I: Characterization of the wheel/rail dynamic system. 21. H. NAAKE 1953 Acustica 3, 139-147. Experimental investigation of the vibration of railroad rails. 22. A. GALAITSIS and E. BENDER 1976 Journal of Sound and Vibration 46,437-451. Wheel/rail noise, Part V: Measurement of wheel and rail roughness. 23. E. E. UNGAR and L. E. WITTIG 1980 U.S. Department of Transportation, Report No. of pubUMTA-MA- 06- 0099- 80- 6. Wayside noise of elevated transit structures-analysis lished data and supplementary measurements. 24. L. G. KURZWELL 1977 Journal of Sound and Vibration 51,419-439. Prediction and control of noise from railway bridges and tracked transit elevated structures.