Factors affecting railway noise levels in residential areas

Journal of Sound and Vibration (1977) 51(3), 393-398

FACTORS

AFFECTING

RAILWAY

NOISE

LEVELS IN RESIDENTIAL

AREAS J. G. WALKER

Institute of Sound and Vibration Research, University of Southampton, Southampton S09 5NH, England (Receired 2 December 1976) In order to be able to estimate noise levels in residential areas it is important to understand the mode of propagation of railway noise in open ground conditions. Experiments were conducted to !nvestigate the effect of train type and speed as well as distance from the track on measured noise levels. The presence of cuttings and embankments as well as the houses themselves also affect the noise levels. Data are presented which show the effect of all these parameters and a simple procedure is outlined that allows the maximum noise level at any position in a residential area to be estimated.

1. INTRODUCTION As part of a national survey of railw.ay noise it became necessary to develop a simple method of predicting levels of railway noise in residential areas alongside railway lines. The particular problem involved the prediction of the maximum railway noise levels in 80 areas encompassing a wide variety of residential situations along both sides of 282 km of railway track and including 40 000 houses. The prime requirement was that not only should the procedure be accurate, but that it should be simple to use. The approach made was to develop a set of simple rules that could be applied to any railway environment. The noise level produced at any point in an area is a function of the speed and type of the train, the distance from the track, the presence of cuttings or embankments and the shielding provided by buildings between the railway track and the measurement point. The effect of each of these factors on railway noise was considered in turn. The resultant procedure utilizes an open ground prediction method which is then adjusted for cuttings, embankments and the shielding effect of different building configurations. Throughout this paper the noise level is described in terms of dB(A) because of its wide use in environmental noise studies.

2. EFFECT OF DISTANCE FROM THE TRACK ON NOISE LEVEL Several investigations into the effect of increasing distance from the track have been carried out (see, for example, references [I-5]). A more recent investigation was made by Tubby [6] who looked in detail at l~he way in which noise levels at different distances from the track depended on the particular wheel configuration in the train. He found thai; his data compared well with Rathe's [7] theoretical studies if the train were considered as an array of point sources withspacings corresponding to the axle spacing on the train. Tubby's data together with Rathe's predicted levels are shown in Figure 1 for a train speed of 140 km]h. The cor393

394

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respondence is good and the data in Figure 1 were used as the basis for estimating the noise levels at different distances from a railway track. 3. THE EFFECT OF SPEED ON NOISE LEVEL Investigations reported in several papers [1-4] have shown different relationships between noise levels and train speed. However, for the typical range of train speeds under consideration (80-160 km/h) the differences likely toresult from the use of different relationships is of the order of 2 dB(A) although the absolute level depends on the prediction procedure chosen (e.g., see Figure 1).

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Figure 2. Relation between train speed and peak level (dB(A)) (from reference [2]). ----,

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The Walker, Allen and Large noise level/speed relationship [2] was used in the procedure. Their relationship was developed from experimental data, and is shown in Figure 2. The change in level for a change in speed from V, to 1"2for a long train is given by ALa ~ 251og,o x Vi/V2, whilst for short trains it is given by ALa ,~ 401oglo F,/F2.

395

FACTORS AFFECTING RAILWAY NOISE LEVELS

4. EFFECT OF CUTTINGS AND EMBANKMENTS ON NOISE LEVEL After having estimated the noise levels for tracks at grade and for the effect of changing speeds and distances for the open ground situation, the estimated level is corrected for the effect of cuttings and embankments. In order to determine these effects a series of measurements of railway noise alongside a cutting and embankment was made. Four simultaneous recordings were made for different cutting and embankment heights, and the difference in noise level for each position was calculated. These differences for 2 distances from the railway lines are shown in Tables 1 and 2. In both cases the difference was quoted with reference to a cutting or embankment of 1 m height as it was apparent that for a cutting or embankment of this height the noise level did not differ noticeably from the predicted noise level for a track at the same level as thd surrounding ground. TABLE 1 Reduction hz noise level in dB(A) caused by a raifivay cutting, at two distances from a 2-track railway Cut depth difference (m) (re: 1 m) Distance (m) 25 Mean (S.D.) 40 Mean (S.D.)

Near track

Reduction in noise level (dB(A)) 3 5 ~ r ~. , , ,~ , Far Near Far Near Far track track track track track

2.67 (0-52) 3-00 (0"89)

2.33 3.67 2.83 (0"82) (0"82) (0.75) 1.3 3.67 1.3 (--) (0"82) (--)

2 A

,

5.67 (1-75) 4.67 (1"86)

5.33 (1.21) 3-0 (--)

TABLE 2 Re&tction in noise level in dB(A) caused by an embankment at two distances from a 4-track railway Bank height difference (m) (re: 1 m) Distance (m) 25 Mean (S.D.) 50 Mean (S.D.)

Reduction in 2 r A ~ Near Far track track 1-88 (0"84) 0.80 (0-84)

noise level (dB(A)) due to bank 5 7 r A ~ , A , Near Far Near Far track track track track

2.50 3.00 (1"29) (1-41) 2.0 1-25 (--) (0-96)

6.00 3"63 8.00 (2"45) (1"99) (1"15) 3.00 0.2 4.0 (--) (--) (--)

Although the data is limited to relatively few train measurements it seems clear that there is only a small reduction (maximum 6 dB(A)) in noise level due to cuttings. This is much less than those predicted by Kurze and Beranek [8]. The shielding effect of embankments and cuttings is the same for diesel and electric hauled trains even though the major source of motive power noise is higher above the track for the diesel locomotives. The different shielding for the near and far lines is also clear. A further research programme is in progress to carry out a more comprehensive study of these effects and to carry out more detailed study of the theoretical reasons for the data obtained.

396

j.G. WALKER 5. EFFECT OF HOUSES ON NOISE LEVEL

Perhaps the most important factor affecting noise propagation away from railway tracks is the presence and configuration of buildings alongside the track. In order to study thes~ effects, noise levels were measured at a total of 61 points in 7 different areas. The house~ providing shielding had 2 storeys and included examples of detached, semi-detached and rows of terraced houses. Noise levels in dB(A) were measured simultaneously at 2 or positions in an area for several train pass-bys, including both diesel and electric powered trains. One position was always in clear view of the track and unobstructed by any barriers, With the level measured there used as a base, the open ground noise levels at each of the other positions for each pass-by were estimated. The differences between the levels estimated in this way and the measured levels gave the noise reductions due to the houses and any embankment or cutting. By using the data presented in Tables 1 and 2 it was possible ta estimate the effect of the houses alone. It appears from the measurements that the rows ot det.ached or semi-detached houses behave more like insertion losses than true barriers, and the distances between the track and the houses or the houses and the measurement point did not affect the level reduction. The effect of various housing configurations is summarized in Table 3, which includes all the useful data obtained at the sites. TABLE 3

Summary of reduction in noise levels due to houses Type of house

Detached/ semi-detached

Terraces approx. 150 m long

Number of rows

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Terraces approx. 300 m long ,A

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Number of sites Number of trains Excess attenuation dB(A) Standard deviation (dB)

3 12 8.3 1.84

7 30 11.9 3.06

(6)~ (24) (12.9) (1.69)

1

>-2

11 28 14.7 2.7

7 16 17.1 2.2

t For each successive row of detached or semi-detached houses add 4 dB(A) to the level reduction. ~tOmits data for reduction at one site that was much less than expected compared to the other sites. TABLE 4

Difference in dB(A) between the noise levels measured at a reference position (A) and2 other positions (B, D) in a residential area for both electric and diesel powered trains on a 4-track railway. Tile differences are due to houses and increased distances from track Mean level differences A (dB(A)) and standard deviations a Trains on near tracks Trains on far tracks Motive power All Electric Diesel

,A

A-B Number A tr Number A tr Number d o

14 15.0 1"42 7 15"0 1-17 7 15.0 1.73

A

A-D 11 22-5 2"10 5 22"5 2"28 6 22"5 2"05

A-B 10 10.5 1"61 4 9"5 1-73 6 11"5 1"13

A-D 9 17.0 1"94 3 15"0 -6 18.0 1"16

FACTORS AFFECTING RAILWAY NOISE LEVELS

397

Several points require further discussion. Firstly, it is clear that the buildings affect the noise from all train types in the same way. Secondly, the noise is affected during propagation across railway tracks. There is a larger difference in level between the near and far tracks on a 4-track railway than would be expected from distance considerations alone. It appears that the presence of ballast and the lines themselves probably affects noise levels by a significant amount, which is more critical for the near positions. Both these points are illustrated in Table 4. The effect of propagation across a 2-track railway is much less marked, being about 1-2 dB(A). For these reasons the noise level is normally predicted for the noisiest trains on the near track. In addition the presence of a high embankment can reduce the effect of houses (by up to 4 or 5 dB(A)) and can effectively reduce the number of rows of houses. The presence of gaps in rows of terraced houses can reduce the effect ofthe houses considerably in the region of the gaps, dependant on the size of the gaps. 6. SUMMARY The data presented above can be used to predict the maximum noise level from railway operations in any residential area. The procedure is summarized below, together with a worked example. Step 1 : Estimate the noise level at any given distance in open ground for a train at 140 km/h by using Figure 1. Step 2: Correct for different speed by using Figure 2. Step 3: Correct for effect of embankment or cutting by using Tables 1 or 2. Step 4: Correct for housing effect by using Table 3. The corrected level is the noise level that will result from the noisiest train type (usually the fastest) using the nearest line. Worked example: 84 dB(A) Step I" Estimated level at 100 m, 140 km/h +1 dB(A) Step 2" Correction for speed of 160 km/h 85 dB(A) - 3 dB(A) Step 3: Effect of cutting (estimated) 82 dB(A) Step 4: 2 rows of semi-detached houses (8 + 4 dB(A)) - 1 2 dB(A) 70 dB(A) Estimated maximum noise level This procedure was used to estimate noise levels for the 40 000 houses chosen in the survey sample. Noise measurements have been made at about 2000 houses. The data is at present being analysed and theaccuracy of the technique will be determined. Until then it will not be possible to make statements about its accuracy.

REFERENCES 1. S. PETERS1974 Journal of Sound and Vibration 32, 87-99. The prediction of railway noise profiles. 2. J. G. WALKER,G. ALLENand J. B. LARGE1974 Paper presented at the Second Interagency Symposium of Unicersity Research hi Transportation Noise, Raleigh, North Carolina, June 1974. Planning and railway noise. 3. THE PHYSICSSECTION, BRITISHRAILWAYSBOARDRESEARCHAND DEVELOPMENTDIVISION 1974 Process Technology Group Technical Note TN.PHYS.4. Railway noise and the environment. 4. J. E. MANNINGand L. G. KURZWEIL1974 Proceedings ofblternoise 74, 265-268. Prediction of wayside noise from rail transit vehicles. 5. S. LJUNGGI~.ENand S. H. O. BENJOARD1972 Byggmasteren, 1. Train noise from the point of view of planning.

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6. J. A. Tt;Bn'," 1974 ALSc. Dissertation, Institute of Sotmd and Vibration Research, Southamptot University. The prediction of railway noise. 7. E.J. RA'rHE 1969 Journal of Soltnd and Vibration 10, 472--479. Note on two common problems o sound propagation. 8. U. KtJRZE and L. L. BERA~EK 1971 in Noise and Vibration Control (ed. L. L. Beranek). New York McGraw-Hill Book Company, Inc. See Chapter 7. Sound propagation outdoors.