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Report No. 3982 _'_ - _ _ - D I i:i

l

Experimental Study of the Effect of the Difference

Between "Hard" and "Soft" Ground Surfaceson Truck Noise Measurements

November 1978

_I'1/

_/ Prepared for:

United States Environmental ProtectionAgency

i _.

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i.!

Report No. 3962

_ EXPERIMENTAL STUDY OF THE EFFECT OF THE DIFFERENCE BETWEEN"HARD" AND "SOFT" GROUND SURFACES ON TRUCK NOISE MEASUREMENTS

! _ November 1978

I][

i_ Contract No. 68-01-4467

Task Order No. I

Submittedto:Y _ United States Environmental Protection Agency_ Office of Noise Abatement and Control

Washington, D.C. 20460F,4il

Submitted by,'

#_I Bolt Beranek and Newman Inc.BO Moulton StreetCambridge, MA 0213B

W

, Report No. 3962 Bolt Beranek and Newman Inc.

{

ABSTRACT

m

Data on truck noise measurements have been gathered for two

trucks, operating in accordance with the Bureau of Motor Carrier

Safety Noise Regulations, over "hard" and "soft" sites, aod forvarious intermediate surface conditions. The results, averaged

for all operating conditions, indicate a difference between hard IIand soft sites tha_ increases with both the percentage of site

hardness and with microphone distance. The generally accepted

difference of + 2 dB(A) between hard-slte and soft-slte data

specified in the BMCS regulations is seen to be approximately

_'_ correct for IMI tests, but about I dB(A) low for passby _ests at

50 ft. These results confirm those reported by other investigators.

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!Report No. 3962 Bolt Beranek and Newman Inc,

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TABLEOFCONTENTS

page

ABSTRACT .................................................. ili

LIST OF FIGURES ........................................... vLIST OF TABLES ............................................ vll

SECTION i. INTRODUCTION 1

2. RESULTS AND CONCLUSIONS ...................... 2

3. BACKGROUND ................................... 3

,_ 3.1 Analysis ................................ 3

3.2 Prior Experimental Work ................. 6L_

4. MEASUREMENTS ................................. 8

_.l General ................................. 8

_.2 Instrumentation ......................... i0

i__/ 4.3 The Trucks .............................. Ii

4.Q The Tests .............................. 14

_= 5. DATA ANALYSIS PROCEDURE ..................... 16

il 6. D_scussloNOFRESULTS.......................35REFERENCES ............................................... 39

i

!i_ A_EMD_N_:..............................................A-I

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Report No, 3962 Bolt Beranek and Newman Inc.J

LISTOFFIGURES

_. page

Figure 3.1 Two sound paths from a noise source (S), to areceiver (R), near the ground ............... 4

4.1 View across 150 ft wide runway used for

vehicle noise tests ......................... 9

I_ 4.2 Schematic diagram of test site -- Westfleld-Barnes Airport, Westfield, MA ............... iI

i_ 4.3 Instrumentation used to record noise data .., 12

_, 4.4 Gasoline-powered "straight truck" used as_! noise source ................................ 13

_ 4,5 Diesel-powered tractor semitrailer truck usednoisesource 13_ _,_ as .............................

!_ 5,1 Hard slte/soft site noise level differences as

" a function of microphone distance: IMl -i_ diesel- rightside , 20

I: 5,2 Hard site/soft site noise level differences as_i a function of microphone distance: IMI -_ diesel--leftside 21• ,.*,.*****,,,,*..*.***.*..

_ 5.3 Hard site/soft site noise level differences asi

{ a function of microphonedistance: !M! --gas --right side ............................ 22

5.4 Hard site/soft site noise level differences as

a function of microphone distance: IMI -

_ gas--leftside 23*.,***,*****.************,°,.

5,5 Hard site/soft site noise level differences as

I_ a function of microphone distance: Diesel_& passbys - 35 mph - right side ............... 24

5.6. Hard site/soft site noise level differences as

a function of microphone distance: Dieselpassbys - 30 to 35 mph - left side .......... 25

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Report No, 3962 Bolt Beranek and Newman Inc.

LIST OF FIGURES (Cont.)

page

'' 5.7 Hard site/soft site noise level differences asa function of microphone distance: Diesel

" passbys -- 45 to 55 mph - right side .......... 26

5.8 Hard slte/soft site noise level differences as

a function of microphone distance: DieselI_ passbys --45 to 50 mph --left side ........... 27

5.9 Hard site/soft site noise level differences asa function of microphone distance: Gas

_I passbys -- 35 mph -- right side ................ 28

5.10 Hard site/soft site noise level differences asa function of microphone distance: Gaspassbys -- 35 mph -- left side ................. 29

[,i 5.11 Hard site/soft site noise level differences asa function of microphone distance: Gas

_ passbys - 45 mp_ -- right side ................ 30

_' 5.12 Hard site/soft site noise level differences asa function of microphone distance: Gas

I_ passbys -- 40 mph -- left side ................. 31t_

5.13 Hard slte/soft site noise level differences as

iI a function of microphone distance: Total IMI . 325.14 Hard site/soft site noise level differences as

,, a function of microphone distance: Totalpassbys ...................................... 33

5.15 Hard sitesoft site noise level differences as

I_ a function of microphone distance: All data . 34_mm

6.1 Comparison of results from present experi-

!_ ments with those of previous studies at 50_ ft. Hard site minus soft site noise level

difference vs percentage of site hardness .... 36

I_ 6.2 Sound level difference between a i00_ hard_& site and a typical "soft" (i.e., 32% hard)

site, as a function of microphone distance ... 38

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Report No. 3962 Bolt Beranek and Newman Inc,

.__] LISTOFTABLES

page

i.! Table 3.i. Results of measurements of truck noise at softvs hard sites, as reported by other investiga-

ftots .......................................... 7

; 5,1, Percentage of surface hardness used in subse-

_ quent computations ............................ 16

A.1. Serial numbers of instruments used for hardslte/soft field measurements ................ A-2

im

I_ B.1. Measured sound levels. Each value is the

average of five measurements ................. B-2

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il.Report No. 3962 Bolt Beranek and Newman Inc,

1. INTRODUCTION

The Department of Transportation Bureau of Motor Oarrier

i,_ Safety Regulations for Enforcement of Motor Carrier Noise Emission

Standards (49 CFR 325) specify in some detail the requirements

i_-- for sites at which motor carrier noise is to be measured for en-forcement purposes. Included in these requirements are the pro-

visions that measurements must be made between 35 and 83 ft

i,_ (10.7 m and 25.3 m) away from the center line of the traffic lane

_ traveled by the vehicle and that the results are to be interpreted

_ _ differently for "hard" and "soft" sites.

iJI_'._ The regulations define a "hard" site as "any test site havingthe ground surface covered with concrete, asphalt, packed dirt,

I: gravel, or similar reflective material for more than 1/2 the dis-tance between the [traveled lane] and the microphone location

_ point." A "soft" site is "any test site having the ground surface

,_ covered with grass, other ground cover, or similar absorptive

i material for 1/2 or more of the distance between the [traveled

_,I_ lane] and the microphone location point."

_I _ The regulations indicate that the difference between noiselevels observed at hard sites and at soft sites will be + 2 dB(A),

regardless of the distance between the measurement microphone andthe traveled lane. The purpose of the work described here was to

obtain limited additional experimental data on the difference in

noise levels between hard end soft sites, particularly for micro-

: phone spacings of less than 50 ft (15.2 m). In addition, infor-

I!matlon was obtained pertinent to the pos@ibility of enforcingtruck noise limits with measurements made at distances less than

_ the 35 ft (10.7 m) minimum distance allowed by the regulations.

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Report No. 3962 Bolt Beranek and Newman Inc.

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ii 2. RESULTS AND CONCLUSIONS

The results and conclusions, based upon measurements of two

L.! trucks, can be summarized in four major points.

i-__ First, the difference between maxilnum truck noise levels ob-served at "hard" sites and corresponding levels observed at "soft"

sites is a strong function of the percentage of surface hardness,

I_ and this difference increases with the percentage of hardness. W

For example (see Fig, 6.1), at a measurement distance of 50 ft

I_ (15.2 m), the difference ranges from about 1 dB(A) for a 25% hard

! _ site to 3 to 4 dB(A) for a 100% hard site.

ii_ Second, the hard-site-to-soft-site difference is a function

:!I_ of microphone distance: The greater the microphone distance, thei_ greater the difference. For example (see Fig. 6.2), going from a

100% hard site to a typical soft site yields a difference of 1.5

I! I_ dB(A) at 25 ft (7.6 m), and about 2.5 dB(A) at 50 ft (15.2 m).

!i Third, the results of this study generally confirm the re-

.... _ sults of previous investigators for IMI/low-speed-acceleratlon

_ _ truck operations. However, for truck passby operations, the pres-

_i_ _ ent results indicate a hard-site-to-soft-slte difference about

'_i 0.5 dB(A) less tl_an reported by others.

, 'i

_. Finally, these data indicate that the 2 dB(A) difference be-

I_ tween hard- and soft-site truck noise levels specified in BMCS

I_ re'gulations is slightly low, but approximately correct. However,

_ it can vary by ± 1 dB for the range of conditions that.could occur

in field enforcement practices.

" _ _"Pereentage of surface hardness" is defined here as the percentageof pavement along the shortest path f_om the vehicle track to the

_._ microphone. See Table 5.1.

,! 2


i J# 3. BACKGROUND

3.1 Analysis

Although a considerable body of experimental data has been

accumulated on the subject, the effect of the ground surface onthe propagation of sound from a source to a receiver Is still

imperfectly understood. (Appendix O contains the bibliography of

L'_ literature reviewed for this report.) As stated by Piercy et aZ.

[_], this is "an intricate and rambling subject both mathemati-cally and conceptually." Some of the reasons why this is so are

that the propagation losses are intimately dependent upon the

geometry of the configuration, She acoustic impedance (complex)

o9 the ground, and local atmospheric inhomogeneities. Some of_a

_ these parameters cannot be controlled, or even defined, for any: given test configuration.

:_ _ Consider the geometry of Fig. 3.1. Two sound ray paths are

i__'_ possible between the source, S, and the receiver, R: The direct

.i_ _ path has a length, rl, and a longer reflected path has a total

length, r_. If we assume plane waves (i.e., no spherical diver-

[_ genee) and a locally reacting ground surface, the ratio, C,of

the acoustic pressure of the reflected wave at R to that of the

dlrecwaveis:G

PrefleetedZ slnB-po

C = = (3,1)° Pdlrect -g --"__-i.

,i._ This is called the reflection coefficient of the ground, where pcb' is the characteristic impedance of the air.

If the ground surface is acoustically very hard and the re-

_ fleetions are specular (i.e., as from a mirror), then Zg >> pc

and:

_" C = i. (3,2)

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In this perfect-reflection case, the two waves will add together

at the receiver when r2 - rz is an integral number of wavelengths,

and they will interfere or cancel when r2 - r_ is an odd number

'_' of half wavelengths. Obviously this summation or cancellation

effect will be a function of sound frequency and geometry.

On the other hand, if_the ground is acoustically very soft- m

j._ (i.e., Zg << pc), then C approaches - i, and there is a 180_ phasereversal of the wave upon reflection. Then the interference pat-

_ tern reverses, and the direct and reflected waves cancel for

r2 - r_ equal to an integral number of wavelengths, and they add

_ _. for r_ - r_ equal to an odd number of half wavelengths.

: Finally, for any finite value of Zg, a 180 ° phase reversal;_ . (C = -i) occurs for grazing incidence as B approaches zero. Be-

cause r_ essentially equals r2 at grazing incidence, the two

wavescancel plane-wavepropagationcannotoccurThe impedance of the ground, Zg, is a complex function of

i _ frequency and angle of incidence. It changes with the type of

_. ground cover, water content, and other climate-dependent variables.

I_ In the same way, the effective lengths of the direct and reflected

sound paths r_ and r2 change because of local atmospheric inhomo-

i _ genities and differences in the heights of the many separate noise

sources of a truck. Finally, the ground is seldom perfectly flat,"_,I!'_ and the surface irregularities that are comparable to or larger

m than the sound wavelength can produce sound scattering rather than

I-_ specular reflection. It is because of these complexities thatthe prediction of sound propagation near the ground is far more

'.... *This is not true for the more general case of spherical waves,however. For spherical waves, a ground-wave term analagous tothat existing in electromagnetic propagation takes over to pro-

-_. vide some signal under grazing-incldence conditions.

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_i complicated than the simple description that we have given here.JA

In general, any real configuration, such as that used for motor

carrier noise emission regulation, cannot be handled analytically' I

and must be treated empirically, with some guidance provided from

1,7 the simplified analytical picture.

3.2 Prior Experimental Work

Other investigators have published data on the effects of

soft vs hard sites on truck noise measurements. Several of these

i_ studies are summarized in Table 3.1. An interesting trend is re-

vealed by comparing the first three rows -- data for trucks aecel-

.._H crating at low speed --with the second three rows -- data for

trucks passing by under power. The former indicate a hard-site-_a

_ i_ to-soft-slte difference of 2 dB(A); the latter indicate a corres-ponding difference of about 3 dB(A). This trend is also noted

' i_ in Her. 3, where the author cautions that it is in need of further

' verification. Of course, the generally accepted difference is

_ 2 dB(A) for all test conditions, as specified in the regulation' _,_ and other literature [4].

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ii 4, MEASUREMENTS

,: 4.1 GeneralL*

Field measurements were performed July 27, 28, 31, and

_ August l, 1978, at Westfield-Barnes Airport in Westfield, Mass-L_

achusetts. An abandoned runway, currently unused but maintained,

was used as the "road." This runway is about 3300 ft long and

: ,_i 150 ft wide. It has an asphalt surface, with both shoulders

grassy and level.

Westfield-Barnes Airport was chosen because of the excellent

_ condition of the unused runway and its relative proximity _o BoltBeranek and Newman's Cambridge offices. A runway, rather than a

highway, was selected as the ideal test site because its width_i allowed a large working area for microphone layout and because

i_ there were no paved shoulders. (See Fig. 4.1.) Receiver locations" could then be varied incrementally, from soft to hard. That is,

ii the locations could be all on the grass beside the runway (soft);

ii _ there could be various combinations of partially hard, partiallysoft locations_ or all the locations could be on asphalt (hard).

: _ Aircraft activity at the airport was light. When an occa-

f_ sional aircraft produced noise that might have interfered with the

truck noise measurements, the truck noise measurements were repeated.

I_ The weather, during the measurement period varied somewhat,a_

but conditions were generally fair, clear, and cool. Temperatures

_ averaged 60°F; wind speed ranged from 0 mph to 10 mph. No measure-

_ _ ments were taken during occasional wind gusts of up to 15 mph.

_., The coolness assured that the pavement did not get hot and soft,

-- and its characteristics are believed to have remained constant.

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FIG. 4.1. VIEW ACROSS 150 FT WIDE RUNWAY USED FOR VEHICLE NOISE TESTS.

W.4

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:I Five 10-ft (3-m) wide lanes were marked out with traffichl

cones and spray paint. Lane 1 was nearest the edge of the runway

. and Lane 5 farthest from it. (See Fig. 4.2.) Tests were runi _,_! with the noise source vehicle in each of the five lanes. The

_ microphones were moved with each lane change to maintain a con-.__'" stant distance from the source. In this way, the percentage of

-- hard surface between the source and the microphones was varied.

4.2 Instrumentation2_

_'_ GenRad 9601 microphones were placed at distances 25, 31, 36,

and 50 ft (7.6, 9.4, ll, and 15.2 m) from the centerline of the_:i lane being used for the tests. A reference microphone was placed

50 ft (15.2 m) from the lane centerline on the opposite side, All

L IT microphones were at a height of _ ft (1,2 m). Each microphone

was connected through a cable to a GenRad 1982 Sound Level Meter,

_ which provided a digital read-out of the maximum sound level ob-

_ rained on the "fast" response scale. See Fig. 4.3. These meters

i__I hold this maximum reading until they are manually cleared. Ant_

i_ anemometer was used to record wind speeds. Details of the sound

_i_ measurement equipment are listed in Appendix A.

4.3 The Trucks

Two trucks were used: a gasoline-fueled and e diesel-powered

• _ i_ truck. The gas, or straight truck, was a rented U-Haul, as shown

in Fig. 4.4. This truck has a V-8 engine of 330 cu in. displace-

ment, and a manual four-speed transmission. It is 28 ft long.

(Its U-Haul equipment number is $633TP6092C.)

_ The diesel truck was a tractor semitrailer. This truck is

" a 1975 Brockway, Model EL-380. See Fig. 4.5. The engine is rated

!,_ at 425 horsepower; it is manufactured by Caterpillar and has six

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I"_'_ I /SOURCE LOCUSASSUMED/tBXAMPLE SHOWNFORLANEI)

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I 5o,I' _ R_ERENCEM,CROPHONEI._ I

TEST LANE) _ I

MICROPHONE POBITIONB(FROM CENTER LINE OF TEST LANE)

• I I, Im ,.J .J ,,J .J -I

I ,_ I" ASPHALT RUNWAY .... l_ GRASS _ I

_ FIG. 4.2. SCHEMATIC DIAGRAM OF T_ST SIT_WESTFIELD-BARNES AIRPORT, WESTFIELD, MA.

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,I'_ FIG. 4.3. INSTRUMENTATION USED TO RECORD NOISE DATA.b_

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Report No. 3962 Bolt Beranek and IRew_an Inc,

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i, FIG.4,4, GASOLINE-POWERED"STRAIGHTTRUCK"USeDAS t_OISE_OURCB,FA

i

I) _:. _ "--. ---_.:"T_'-":- --_---*_"-L_

_'_ FIG. 4,5, D_SEL-POWERED TRACTORSEMITRAILERTRUCK USEDAS NOISE SOURCE.


• i

.! cylinders. The exhaust system is manufactured by Riker. The

exhaust is from a high stack on the right side of the cab. The

' trailer is 24 ft long.b

The use of only two trucks limits the general applicability

I._ of the data reported here.

i, 4.4 The TestsI '4

Two types of tests were performed with each truck in eachr_

P__ lane. One was a stationary test, the other a paseby. For the

stationary test, the truck first was run at idle, then was revved

up to full throttle, and the accelerator was then immediately re-

leased, This test is referred to as an Idle-Max-ldle (IMI) test,

and noise measurements were made on both the right and left sideLJby turning the truck around. This was repeated five times in

each lane, on each side.

Passbys were also done in each lane, on each side. These

tests were done at two speeds: a low speed of 30 to 35 mph, and

a higher speed of 40 to 50 mph. Speeds for each passby were re-

corded. Because of a very slight grade in the runway, the speeds

were slightly greater during the downgrade runs than during the

_ upgraderuns.

The test procedure was as follows: After the instrumentation

I was set up for Lane i, five IMI tests for both the left side and

the right side of the straight truck were performed. Then, again

with the straight truck, 35-mph passbye and then 45-mph passbys

_' were run, also five times per side. The maximum sound level at

_"° each receiver location was recorded for every run. Since the

truck ran both up and down the runway, both right- and left-slde

,_, paseby results were quickly acquired. The entire procedure was

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!,.I then repeated in the same lane with the diesel truck. Measure-ments of the diesel truck were taken with and without the trailer,

and the presence of the trailer did not appear to affect the noise

levels, but there were, then, more tests performed with the diesel

truck than with the gasoline truck. After all tests on both'" trucks were completed, the entire procedure was then repeated for

Lanes 2, 3, 4, and 5.* By changing to lanes farther from the •!i shoulder while maintaining constant source-to-microphone spacings,

_ the sound path was changed from being essentially all over a soft

['_ surface (Lane I), to partially over soft and partially over hard,

' until ultimately, in Lane 5, the path was essentially all over

I_l a hard surface. Each time the lane being used was changed, allthe microphones were moved to maintain the 25, 31, 36, and 50 ft

{_ (7.6, 9.4, iI, and 15.2 m) distances from the lane centerline.All the data, averaged over the five runs in each configuration,

._ _ _ are given in Appendix B.!!

I

"No passby data were acquired with the diesel truck in Lane 2.T

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5. DATA ANALYSIS PROCEDURE

After calculating means and standard deviations for the five

LJ runs of each test case, five basic steps were used to determine

the relative change in noise level with response to the number of

feet of "hard" surface (asphalt) vs "soft" surface (grass) overwhich the sound had traveled. All analyses were done with the

!!_ five-run averages listed in Appendix B.

Stepi

_i The "percent of surface hardness" along the sound path

i _ from the source to each microphone was determined for each_ test lane configuration. These values are tabulated below.

t

',I_ TABLE 5.1. PERCENTAGE OF SURFACE HARDNESS USED IN SUBSEQUENT COMPUTATIONS.

i_ Hard-Surface DistancefromNoiseSource' Distancefrom to Microphone(ft)

' ! _ ;enterlinetoEdge

! _ Lane ofPavement 25 31 36 50

_ i 5 20% 16% i_% i0%

3 25 io0 81 69 50

;'_ h 35 I00 i0o 97 705 _5 IO0 i00 iO0 90

i Step 2

For each truck and truck-operating condition_ and for

each microphone position applicable to that truck and oper-

i_ ating condition, the data for the five lanes were grouped

together. Within each such group, the level observed at the

II reference (far-side) microphone during truck operation in-- Lane 5 was arbitrarily selected as a standard. Each of the

,_. 16


t

differences between this reference level and the reference

levels observed during truck operations in the other lanes

was then applied to the corresponding measured data for the

other lanes, for that microphone spacing.

D_ This procedure normalized the measured levels for each

microphone spacing and corrected for any change in truck

noise output from lane to lane.

For each of the groups of measurements normalized in

i_ Step 2 (i.e., for the normalized data from five lanes of oper-

ation corresponding to each microphone spacing, truck, and

: _, operating condition), a linear regression of the form L =: a (%H) + b was computed for the five data points. The values

_: h_ of percent hardness (%H) were taken from Table 5.1. Using

_ this equation, the noise levels that would have been observed

at 0%, 25%, 50%, 75%, and 100% hardness were estimated.

This procedure yields levels at each microphone spacing

_ that are directly comparable, in terms of percentage of hardsurface under the sound paths.

_ The level at 50 ft (15.2 m) for 0% hardness from Step 3was then selected as a reference and subtracted from all other

_ levels for various microphone spacings and hardness percen-tages for each of the following truck operating conditions:I!

IMI - diesel- right side

IMI - diesel - left side

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_,_

IMI - gas - right side,I

IMI - gas - left side

.... Fassbys - diesel - right side - 35 mph

_ Passbys - diesel - left side - 30 to 35 mph

Fassbys - diesel - right side - 45 to 55 mph

diesel left side 45 to 50 mphFassbys

Passbys - gas - right side - 35 mph

Passbys - gas left side - 35 mph

Passbys - gas - right aide - 45 mphi Passbys - gas - left side - 40 mph.

• [_ Thls yielded changes in level (AL) as a function of dis-

tance and % hardness that are plotted on Figs. 5,1 through 5.12.

f_ Step 6

z Linear regression equations were computed of AL as a

function of microphone spacing (distance, D) for each of the

i_ _ data sets on Figs. 5.1 through 5,12. The equations are

shown on the figures.

;" The results of all IMI tests were then combined; they are

_,_ illustrated on Fig. 5.13. The combine_ results of all passbyI_ tests are shown on Fig. 5.14. Finally, the combined results of

i all tests are illustrated on Fig. 5.15.

_ _ Note that each of the "data" points on Figs. 5,1 through

_ 5.15 represents a difference (Step 4) between interpolated numbers(Step 3), normalized (Step 2) from averages of raw data. Thus,

[ the actual number of raw data observations contributing to each

'il)I'_ 18 li"


of these points is obscured. In general, however, each point on

Figs. 5.1 through 5.4 and 5,9 through 5.12 is interpolated from

regressions fitted to 25 raw data points (averages of five runsfor each of five lanes). Each point on Figs, 5.5 through 5.B is

interpolated from regressions fitted to 40 data points (averagesfrom five runs, for four lanes, with and without the trailer).

Each point on Fig. 5.13 is similarly based upon I00 raw data_Z values, and each point on Fig. 5.14 is derived from 260 raw values.

_ The points on Fig. 5.15 are derived from 360 raw observations.

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Report No, 3962 Bolt Beranek and Newman Inc,

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('a I B l "'_'" 75% HARD _L i 21,04--'1I.'I2 10(]D --

_......_ &'''" 50% HARD L_L 19"79 " 10,75 log D,., .-"".-- 25% HARD AL ]7,9Z - 9,99 Ioq D

i!_ -,- O°/oHARD_LIs.ss-9.57Jooo._ I I r I i i i

[_ 10 20 30 40 50 60 70 8090]00=,, DISTANCE D (fl)

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(_ -,,- oO,'oHARD_L=3S.B4-Z2.71,o_OI==

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F! FIG. 5.3, HARD SITE/SOFTSITE NOISELEVEL DIFFERENCESAS A FUNCTIONOF MICROPHONEDISTANCE: IMI- GAS- RIGHT SIDE.

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mll_ 0% HARDZ_L= 31.50-1B.60 IoQD: -I_ I r I I r r ] t

I-_ 10 20 30 40 50 60 70 80 90100

LJ DISTANCED (ft}

::_ FIG.5.4. HARDSITE/SOFTSITENOISELEVELDIFFERENCESAS A FUNCTIONOF MICROPHONEDISTANCE:IMI- GAS- LEFTSIDE.

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,, ,,

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•_0.,_100% HARr, AL = 27.13.. - 14.49 logo J

75% HARD .A L = 27.58 - 15.19 Io9 D ..,.

i _ -8 ---Z_--....A....50%HARD,A.L: 2B.03 15.89lo9D.--_.-- 25% HARD AL 28.02- 16.30 log D

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("_ 10 20 30 40 50 60 70 80 90100

DISTANCE D (ft} i

i ,_, FIG.5.5. HARDSITE/SOFTSITE NOISE LEVEL DIFFERENCESAS A FUNCTION,[ OF MICROPHONEDISTANCE: DIESELPASSBYS - 35 MPH - RIGHT SIDE.

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Report No. 3962 Bolt Beran_k and Newman Inc,

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---0---100% HARD AL = 29.51 -16.90 log D

C p:_ -8 --&.'- 75% HARD AL = 29.6B -17.20 log D -D_ .... &.... 50% HARD &L = 29.67 -17.41 log D

•--_.-- 25% HARD AL = 29.18-17.28 log D

i _ .--m_ 0% HARD AL = 29.64-17.78 log D_ -J2 • I I I r I I I,+_ 1o 20 30 40 _o+o_o80_oloo

++_ D,SrANCeot.)

_, FIG. 5.7. HARD SITE/SOFTBITE NOISE LEVELDIFFERENCESAS A FUNCTIONOF HICROPHONEDISTANCE: DIESELPASSBYS- 45 TO 55 MPH -RIGHT SIDE.

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.--r_.-- 25% HARD AL -" 34,61 -20,26 log D!If} --Jl-- 0% HARD AL = 36.68-22,0910Q D

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'_ -12 --II-- 0% HARDA,L = 34.75 - 20.81 log_, f r I I I I I I++ lo 20 3o 40 5o so Toeo_oloo

DISTANCED (ft)

l+ FIB.B.ll. HARDSITE/SOFTSITENOISELEVELDIFFERENCESAS A FUNCTIONOF MICROPHONEDISTANCE:GASPASSBYS- 45 MPH- RIGHTSIDE•

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.--I:1.-- 25% HARD AL = 35.22 - 20.32 log D

!,_= ---m-- 0% HARD AL = 38.70- _'3.09 log D

= -12 I I I I I I IFa 10 20 30 40 50 60 70 80 90100_'_ DISTANCE D (ft)

FIG, 5.12, HARD BITE/SOFTSITE NOISELEVELDIFFERENCESAS A FUNCTION

OF MICROPHONEDISTANCE:GASPASSBYS- 40 MPH- LEFTSIDE,

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}': I _l_ 0% HARD /%L 32,_'B "19.'_9 log D¢;l }!

:_ II_ I ' I I I I I t r

,_]_ _o zo zo 40 _o so 70 aoso_o(, i_ _ DISTANCE D (ft)

_ FIG. 5.14. HARDSITE/SOFTSITE NOISE LEVEL DIFFERENCESAS A FUNCTION_' OF MICROPHONEDISTANCE: TOTAL PASSBYS.

I 33r!

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._m._ 25% HARD AL = 29.20-16.85 log D7;

_i_,{_ _11_ 0% HARD AL = 29.75 -17.69 log D-m I I I I I I I I

_' _@ 10 ZO 30 40 50 60 70 80 90100_,j_ DISTANCE D (ft)

Ill

FIG,5.15, HARDSITE/SOFTSITENOISE LEVELDIFFERENCESASA FUNCTION

OF MICROPHONEDISTANCE: ALL DATA,

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= ;34 :

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6. DISCUSSION OF RESULTS

The BMCS regulations define a "hard" site as one paved for

It more than 50% of the sound path. A "soft" site has 50% or less

pavement (see Sec. 1 for exact definitions). In practice, a soft

_ site, is rarely less than 32% hard, because it is underlaid byhalf the active vehicle lane and a paved shoulder or breakdown

lane [3]. However, fully hard sites are common.

The IMI test procedure used in this study is generally ac-

}v cepted as being most comparable to results obtained with trucks

accelerating at low speed during roadway operations [4]. Using

this information and the "percentage site hardness" observationmentioned in the previous paragraph, it is possible to compare

¢_ the results of the present study with those of previous inves-

t| tigators, as they are summarized in Table 3.1. This comparison

_ is illustrated in Fig. 6.1. The locations of the data points fromprior studies on the abscissa of Fig. 6.1 are based upon the

differences in the percentage of surface hardness between "hard"

and "soft" sites as reported by the previous investigations.

See the next to last column of Table 3.1.

It is seen that the present results for IMI operations are

_@ quite comparable to those from previous studies. However, thepresent results for passbys are about 0.5 dB(A) lower than

previous results. The reasons for this difference are unknown,

but could be caused by the very small sample of trucks used in

this study.

In any case, there is a clear indication that the noise

level difference increases with percentage site hardness, ratherthan being constant as implied in the BMCS regulations. Fur-

II thermore, the present results confirm the observation of1

i!

35


,!I ,

i,iCl PASSBYS, PRESENT STUDY, FROM FIG. 5.14

_ 0 PRIOR PASSBY TESTS, 2nd THREE ROWS: " OF TABLE 3.l,' I IMI,PRESENT STUDY FROM FIG, 5.13i;_ • PRIOR ACCELERATION TESTS, FIRST THREE;_'_ _ ROWS OF TABLE 3.I

t_f =¢)ul

i,4w 0u

ul 0

..j 0i_J

tra ,.I

om BMCS REGULATIONS

• (= = MOST LIKELY

t_ SOFT- SITE RANGE)

/L_

I r(_'/,',','r((;'(t I rI_ zO ...... _<__"="_ sO BO 100_ % HARD

•_iI_ FIG. 6.1. COMPARISONOF RESULTSFROM PRESENTEXPERIMENTSWITH THOSE" OF PREVIOUSSTUDIES,AT DO FT. HARDSITE MINUSSOFT SITE

NOISE LEVEL DIFFERENCEvs PERCENTAGEOF SITE HARDNESS.

!"l 36J


!,

. Ref. 3 -- that a greater hard-site-to-soft-site noise level

difference occurs for passbys than for IMI tests.

_ The British data indicated in _he last row of Table 3.1

_ are based upon Ll0 levels for free-flowing traffic and can not

be directly compared with the present data for individual trucks.

However, note (Fig. 5.15) that the slope of sound-level differ-

enee vs distance does indeed decrease with increasing percentage

of site hardness, going from about 5.2 dB/dd at 0% hardness to

3.9 dB/dd at 100% hardness, a difference of 1.3 dB/dd.

In general, the decrease in sound level with distance does

_ _ not approach the classic 6 dB/dd for the data reported herein.

' This suggests that the measurements at distances of less than• _._l| 50 ft from the trucks are in the near field of the noise source,

and/or in a region of pronounced ground-reflectlon effects.

Finally, there is definitely a trend of increasing sound

I_ level difference with increasing microphone distance, as illus-

_ trated in Fig. 6.2. In this figure, the difference in sound levels

for a 100% hard site and for a "typical" (i.e., 32% hard) softP_

[_ site is plotted as a function of microphone distance. The hard-

_i site-to-soft-slte difference is about i dB(A) less at 25 ft than

at 50 ft for typical site conditions.

Note that the results illustrated on Fig. 6.2 would shift

up or down relative to the BMOS-specifled correction, depending

upon the choice of percentage of site hardness selected._

tq

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: Report No. 3962 Bolt Beranek and Newman Inc.'rh! ' 1

,! I I I I I I• i,i

--_-- IMI TESTS, FROM FIG. 5.13i' _ --0--. PASSBY TESTS, FROM FIG. 5,14

II--e-- ALL TESTS, FROM FIG. 5.15

i; h

,x W _S

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03:t_ u_

,,MCS_:_! SPECIFIEDCORRECTION

i I,_ 10 20 30 4.0 50 60 70 80 90100

C' DISTANCE D (fl)

i:

i}I_ FIG. 6.2. SOUNDLEVEL DIFFERENCEBETWEENA 100% HARD SITE ANO A TYPICAL

:i_, i_ "SOFT"(i.e.,32% HARD) SITE,AS A FUNCTIONOF MICROPHONEi DISTANCE.

_. 38" If

r_riI,

Report No. 3962 Bolt Beranek and Newman Inc, ,L

'i].i R'EFERENCES

l. J.E. Piercy and T.F.W. Embleton, "Review of Noise Propaga-I,_ tion in the Atmosphere," J. Aoous_. Soo. Am. 61 (6), 1403-

1418 (1977).

lJi 2. E.J. Rickely and R.W. Quinn, "Noise Measurement Data form

Highway Bite Qualification," U.S. Department of Transporta-tion, Transportation Systems Center, final report draft,

I_ 1976. Data as analyzed in Ref. 3.

3. Donald B. Pies, "Assessment of Ground Surface Correctionsfor Motor Vehicle Noise Measurements," Wyle Research Report

_ WCR 77-9,February1977.!

I_ 4. B.H. Sharp, "A Study of Truck Noise Levels and the Effectof Regulations," Wyle Laboratories Report WE 74-8, preparedfor U.S. Environmental Protection Agency, December 1974.

_;_ Data as reported in Ref. 3.

i!

!ii!i_"_ _. M.E.Del_ny,,o_.,"Ths_redictionofNoise_evslsLloDue:i

¢,

!,

_,_

f__ 39

, ReportNo. 3962 Bolt Beranekand NewmanInc.r'-

I " '

P

__ APPENDIXA

• ¢

i

Report No. 3962 Belt Beranek and Newman Inc.

TABLE A.I. SERIAL NUMBERS OF INSTRUMENTS USED FOR NARD SITE/SOFT FIELD'" MEASUREMENTS.*

System 25ft 31ft 36ft BOft Ref,

_ Microphone]i 9R1962-9601 6727 5121 2306 1012 5189

Pre_mplifier hPB 1797 1776 193_ 1910PEP._2

IllSLM: 9R1982 0890 0905 0701 0205 1130

iT 18 23 28 29Power Supply:BBN No.

*The name equipment was used for each lane, therefore, the25, 31, 36, 50, and reference equipment were the same inevery ease.

(

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Report No. 3962 Bolt Beranek and Newman Inc.r-

i h

; i,_ TABLE B.I. MEASURED SOUND LEVELS. EACH VALUE IS THE AVERAGE OF FIVEMEASUREMENTS.

p-AverageSound Levels in 86 A Observed

i.-i Test Infor_tlon at Spec fed D_stancesfrom the Truck

Truck Test Lane Ref, 25 ft 3! ft 36 ft 50 ftr_

I_lee_l IHI- rIcJ,'. 94.3 ,6 93.6 ,33 92,7 I.Z 92,k 1,0 BO,7 .7ZMI - let_ 9z,6 ,6 g_.9 ,31 92,h .3 92.k .2 9D,h ,_

PleJel,w/trailer IMI - r_h_- 2 92,9 ,3 9_,a ,_ ' 93,6 .2 92.T ,_ 91,6 ,_IHI - ie_. 2 92,0 ._, 94,7 .2 93,8 ,b 9_.0 ,_ 9E,1 ,7IH! - r_nht 3 93.0 .6 95.5 ,& O&.B .6 9_.) .B 90,6 .6

" IMl- ie;"_. 3 92,1 ,7 95,3 ,2 95.5 ,2 03,9 .5 91,3 ,6: " IRI- r1_h_ _ 93,B ,k 95,2 ._ 9_,2 ,3 93.3 .2 90,8 .6

II_l- lef_ k 9!,0 ,3 95.1 ._ 93.i ,2 95,2 ,I 93,7 ,6ZHl- right _ 93,6 ,6 96.1 ,k 95.k .3 9&.5 *k 9_,_ .5Till. lef_ 5 92.0 .5 96,0 .L 95,7 ,3 95.3 ._ 93,3 l,d

_" G_ truck, londe_ It.t1- rlr_t i fi3.0 .5 8_,9 ,_ _I_.3 .6 _3,k ,5 ; 79.9 .2

_ _ IHI - le_ I 82.3 ._ 86.6 .3 03.6 ._ 63.2 .2 BO., .5OL3

IMI - rl£ht 3 03.0 .i 87,9 ._' _.h .O 65.3 .h 81.0 .k

, = Till-rlc_ 5 _2.3 .3 _ 88.1 .P 67.6 .3 O6.0 .i 83.1 ,2

:)_ *' 33_P_i,_ i 75._ .9 78.9 ".7 76.9 1.0 T2.O 72.k .9

i. _i 05_phr_h_ 2 T3.6 .B T_.: LO 70.a .6 73._ 7o.7 1.o

: ,, _=_blo_ _ T_.7 .e 6o.o .T TT,9 _._ 76.3 _,_ n,7 .e* 35_Phrlc_ 3 75,8 1,3 _0.1 _.0 78,7 ,9 73,5 7_.2 1.0

_,*'_;R 35_h lef'; 3 75._ ,7 79,J_ l.o 77,6 .9 76.9 66 7h,O 1,0._ 35=I_br_ch*- I_ 73.9 ,3 7_,_ .6 7_,3 .7 75,a . 73.7 ,5

35_p_le,'_ _ 75.3 ,6 79.9 ,6 70,8 .3 77.6 . 75.5 .3'_i _5=phr_ 5 7_.5 .7 79.6 1.Z _8.3 ,8 77.2 7_.0 .8L,1

35mphlef_ 5 7_.3 1,2 7g.9 ,6 I 79,0 .6 77,9 i7 75,6 1.0

;;_ |_ _5=p_rl_ 1 79.3 ._ E2.3 .5 80.6 .6 76.9 76.8 .7

r'' bO=_ r/_b_ _ 78.6 .8 OO.g 1.2 80.9 1.2 7g.6 : 76.6 1.2" _ph le_t 2 77,9 ,8 b2.3 .3 79,6 ,_ 7_._ 7_,7 .2

"; _5=_hricb_ 3 77,9 ,9 62.3 ,7 B0,6 ,6 _O.O 76,1 .6' _o=_h lef_ 3 77.3 .2 81,9 ,3 Bo,_ .3 79,6 :_ 76.5 ,5

i J_O_phLeSt _ 78.7 ,9 O2.h 1,0 B0,6 .6 79.5 77,9 .6_m_b ri_h_ 5 ?B.l ,6 83.2 .J_ 81.7 ._ 80,7 78.2 ,3

1

!..i_ B-2

, Report No. 3962 Bolt Beranek and Newman Inc.

_, TABLE B. I, (OontCnued)

Avera@e Sound Levels tn _lt(A) O@servad

-- Tes& Information . at Speclfle@ 81s_anc¢s from the 7rwck

pl_el, _,oa_ed 35ml,h r_r_ j _ 87,3 1,0 89,3 1.2 _7_L 1,5 8_,9 1,_ 83.6 _,_

_, 3_ph _e£t I L 89,9 _,5 98,3 I,D gO._ ,1,8 9Q,2 _.5 87,L _,L

30mph icr_ i _6,5 1,_, 90,8 i,_ 89,9 1,6 65,8 ,9 86._ I.L_Smph _Ir_ 3 _5,_ _,3 9O,P Z,k B8,T 1,7 _?,k 1.5 8_,.6 1,7

._, ' 3_mI_h le_'_ 8 8_,3 1.8 i 88,_ Z,? I 87,1 Z.6 8fi,_ _.,_ 83,3 3.,7

,.808.,.,.,.0_P=ph 1e£I, & 8k,9 1,8 88,7 3,.8 8T,z_ Z,k _8,_ 1,8 1 8k,_ 1.8

_. _Smph le£t 5 BS.k ,_ 90._ '_.5 /_8.8 :L.6 87.9 1.8 8S,3 1.8I)l_zeZ- e=_ onz}, [ 38:p@ r_@_ 5 8_,_ ,_, 89,6 ,_ 88,8 .8 87.6 .9 _5,o .9

@8mp_ left 5 83,7 ,h _9,7 ,5 88,9 ,9 _7.6 .7 _5,_ ,_

,_:_':=" , _8°o_.,__ 8,_._o,.__._oo.8_._,., .o_,.__.,.._'" #<I[ u."_.oa@_d k_mp}1 1¢I_i; 3 88,_ 3,,0 9_.9 i,_ 92,_ 3,,3 81,0 Z,Z /_,3. 3,.2

: ; kSmp_, 3.ef$ 3 68,8 3.9 90,k i,(; 88,_ 2,0 87,8 _,0 88,1 1,5

-!,: kSmp_ _ef_ k 88,8 _.5 93.0 ,6 ql.8 .6 go*9 .6 88,;_ ._.,

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_ili BIBLIOGRAPHYOF LITERATUREREVIEWED,i i

Bass, H.E. and Bolen, L.N., "Sound Attenuation Measurements Over•=i_tl Various Ground Covers," J. Aooust. Soc. Am. 62(S1) $42(A) (1977).ii!r: _ Close, W.H. and Clarke, P.M., "Truck Noise - II, Interior and

i[_I'_ Exterior A-weighted Sound Levels of Typical Highway Trucks,"Department of Transportation, Washington, D.C., Final Report

'_I OST/TST-72-2 (1972).!'ii_

Daigle, G.A., "Interference Between Direct and Ground Reflected:_i, Waves Over Grass in the Presence of Atmospheric Turbulence,"

_',J J. Aaoust. See. Am. 63(SI) $59(A) (1978)

_,il Delany, M.E., "Sound Propagation in the Atmosphere - A Historical!

_,_i_: _ Review'" _co_st_o_ 3B 215-218 (1977)._. Delany, M.E., et aZ., "The Prediction of Noise Levels LI0 Due to_:_ Road Traffic," J. Sound V£b. 48(3) 305-325 (1976)

_'i Delany, M.E., Rennie, A.J., and Collins, K.M., "A Scale Modelt_ Technique for Investigating Traffic Noise Propagation," J. So_nd

Vib. 56(3) 325-340 (1978).

Embleton, T.F.W., Piercy, J.E., and 01son, N., "Outdoor SoundPropagation Over Ground of Finite Impedance," J. Aoouet. Soo.Am. 59(2) 267-277 (1976).

,_,_ Embleton, T.F.W., Thiessen, G.J., and Piercy, J.E., "Propagationin an Inversion and Reflections at the Ground," J. Acoust. Sea.Am. 59(2) 278-282.

Galloway, W.J. and Jones, G., "Motor Vehicle Noise - Identificationand Analysis of Situations Contributing to Annoyance," SEA

_i _u 720276, 1060-1074 (1972)........ Hemdal, J.F., et aZ., "A Study of Repeatability of Motor Vehicle

_:_:|_ Noise Measurement Sites," Environmental Research Institute of:,,,'_::__ Michigan, Final Report 3013OO-I-F (1971)

¢:,i Brinton, J.H., Jr., and Bloom, J.N., "Effect of Highway LandscapeDevelopment on Nearby Property," Highway Research Board, National

_i.',' Cooperative Highway Research Program Report 75 (1969).

i

)_!'i_iL, , . ................ ...................

i

ii iiReport No. 3962 Bolt Beranek and Newman Inc.

'_I Hillquist, R.K. and Bettie, R.A., "Measurement of AutomotivePassby Noise," SEA 720275,1052-1059 (1972).

_ii_ Isei, T., Embleton, T.F.W., and Piercy, J.E., "Influence of Re-'_ _ flections at the Ground on Insertion Loss of Barriers," J..... Accuse. So_. Am. 63(SI) $59(A) (1978).

_ _ Kurze, V. and Beranek, L.L., "Sound Propagation Outdoors," in

<_ L.L. Beranek, ed., Noise and Vibration ControZ (McGraw-Hill

i!__ Book Company, 1971), 164-193.

_ii!_ Lyon, R.H., "Outdoor Sound Propagation," in Lecture _, rronspor-_i tation Noise (Grozier Publishing, 1973), 23-31.

ii_;': Lyon, R.H., "Automotive Noise Propagation in Open Areas," inLecture 16, Transportation Noise (Grozier Publishing, 1973),_' 153-163.

Moorhen, van W.K. and Lanier, S.K., "Effect of a Ground Surface_i_ on Acoustic Propagation," J. Aooust. Sos. Am. 61(SI) SIS(A)

!ii:_ (1977).

_;i_i: Parkin_ P.H. and Scholes, W.E., "The Horizontal Propagation ofSound From a Jet Engine Close to the Ground at Hatfleld," J.

4Sound Vib. B(4) 35_-37 (1965).

_ _ Piercy, J.E., Donate, R.J., and Embleton, T.F.W., "Near Horizontal!_iil.il_ Propagation of Sound Over Grassland," J. Aooust. See. Am. 60(S1)

S2(A)(1976).

Piersy, J.E. and Embleton, T.F.W., "Review of Noise Propagationin the Atmosphere," J. Aooust. Sos. Am. 61(6) 1403-1418 (1977).

_C. _ Pies, D.B., "Assessment of Ground Surface Corrections for Motor}:<!_ Vehicle Noise Measurements," Wyle Research Report WCR77-9, U.S._ EPA Office of Noise Abatement and Control (1977).

_.- Sargent, J.W., "Data from Free Flow Traffic Noise Measurements,"_ii! J. Sound Yib. 57(2) 307 (1978).

_: Sharp, B.H., "A Survey of Truck Noise Levels and the Effect of._ Regulations," Wyle Research Report WR74-8, U.S. EPA Office of:_i_, Noise Abatement an_ Control (1974).& ,_

-- Sharp, B.H., "Research on Highway Noise Measurement Sites," WyleLaboratories Research Staff Report WCR72-1, California Highway

ii!!_ Patrol (1972).

< Vargorick, R.J., "Noise Source Definition - Exterior Passenger

/i VehleleNo±se,"0-3

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