NBSIR 82-2610

Highway Noise Criteria Study:

Technical Summary

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Center for Building Technology

Building Physics Division

Washington, DC 20234

October 1982

nsored by:

ieral Highway Administration

RATIONAL BUREAU

.Of STANDARDS

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NBSIR 82-2610 ( J /c

. <r~^ HIGHWAY NOISE CRITERIA STUDY:

TECHNICAL SUMMARY

Simone L. Yaniv and

Daniel R. Flynn

U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

National Engineering Laboratory

Center for Building Technology

Building Physics Division

Washington, DC 20234

October 1 982

Sponsored by:

Federal Highway Administration

U.S. DEPARTMENT OF COMMERCE, Malcolm Baidrige, Secretary

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Director
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ABSTRACT

This report summarizes , at the request of the Federal Highway Administration, a multifaceted research program carried out by the acoustics staff of the National

Bureau of Standards. The program was designed to (1) identify and quantify the

important physical parameters associated with time-varying highway noise caused

by various densities of both free-flowing and stop-and-go traffic conditions;

(2) investigate, evaluate and compare measures and computational procedures for

rating time-varying noise in terms that are relevant to human response; and

(3) determine by means of a laboratory study which among several time-varying

rating schemes best predicts the acceptability and annoyance caused by traffic

noise as heard both outdoors and indoors. The results of this program are briefly described and the implications of the major findings discussed.

i
TABLE OF CONTENTS

Page

1. INTRODUCTION 1

1.1 Background 1

1.2 Goals of Che Study 2 1.3 Organization of the Study 2

2. SUMMARY OF THE HIGHWAY NOISE STUDY 3

2.1 Traffic Noise Data Base (Ref. 1) 3

2.2 Outdoor/Indoor Noise Isolation (Ref. 2) 8

2.3 Effects of Time-Varying Noise on Annoyance 19

2.3.1 Literature Review (Ref. 3) 19

2.3.2 Laboratory Study (Ref. 4) 24

2.4 Relationships Among Frequency Weightings (Ref. 5) 28

3. REFERENCES 29

APPENDIX. DEFINITIONS OF TIME-VARYING NOISE DESCRIPTORS 30

ii
LIST OF FIGURES

Page

Figure 1. A-weighted sound pressure level time history for the

GUDE DR. site, 16 June 1977, 1600 hrs., 15-m microphone .

Figure 2. Cumulative probability distribution of A-weighted sound

pressure levels for the GUDE DR. site, 16 June 1977, 1600

hrs., 15-m microphone

Figure 3. l/3-6ctave band L , L , L , and spectra for the

GUDE DR. site, 16June 1977, 1600 hrs., 15-m microphone,

recording duration of 14,5 min,

Figure 4. Variation of observed values of , L^' and with distance

for interstate and secondary highwlys trld for intersections.

The solid symbols represent the average ratings over all

recordings at all sites of a given type. The error bars

represent the ranges of the ratings

10

13

Figure 5. Variation of observed values of L^q and NPL with distance

for interstate and secondary highways and for intersections

Figure 6. Variation of observed values of TNI with distance for interstate and secondary highways and for intersections 15

Figure 7. Noise Intrusion Reductions, for the three different data

sets, at Test House No 0 6 18

Figure 8. Average and range of Noise Intrusion Reduction values for

all nine test houses 20

Figure 9. Outdoor-to-indoor noise reduction simulated by an electronic

"house filter" 21

iii
LIST OF TABLES

Page

Table 1. Noise descriptors at 30 second intervals - 355 and

Q.O. RD. site, 2A June 1977, 1600 hrs., 15-m

microphone 7

Table 2. 1/3-octave band spectra for the 355 and Q.O. RD. site,

2A June 1977, 1600 hrs., 15-m microphone, recording

duration of 1A.2 min 9

Table 3. Summary of traffic conditions for actual -traffic

noise recordings 11

Table A. Summary of six of the descriptors of the A-weighted

sound levels for the actual-traffic noise recordings 12

Table 5. Summary of test house parameters 16

Table 6. Computed A-weighted noise rating values for the

three-minute time-varying highway noise stimuli

as presented to the subjects in the listening room 26

Table 7. Results of linear regression analyses between

annoyance rating scores and noise indices 27

Table 8. Matrix of correlations between noise indices 27

iv
1. INTRODUCTION

This technical summary was prepared at the request of the Federal Highway

Administration. It briefly outlines and describes a multifaceted research

program carried out by the Acoustics Staff of the National Bureau of Standards.

One of the major goals of this research program was to ascertain which among

several time-varying noise descriptors best quantifies highway noise and

predicts the annoyance caused by exposure to it. Details concerning each

phase of the program have been fully documented in the published reports listed

at the end of this technical summary. Accordingly, the following pages only

briefly summarize the content of each of the already published documents.

As will be seen below, the most important findings of this research program

can be summarized in the following manner: (1) the simpler time-varying

noise descriptors such as the equivalent sound level (L ) and the level

exceeded 10 percent of the time (L^q) are, in the case of traffic noise,

as good as, if not better than, more complicated schemes incorporating

either the range of variability or rate of change of levels with time;

(2) for highway noise the choice of which frequency weighting is utilized

is not critical since one frequency weighting may be predicted from another

with very little uncertainty; (3) so long as the equivalent sound level

(L^) is at or below 50 dB under laboratory conditions; over half of the

exposed people find the traffic eotmd always acceptable; (4) when the

equivalent sound level is 55 dB or greater, over half of the exposed people

find the traffic noise unacceptable.

In view of the above findings it appears that in the case of time-varying

highway noise the measurement and computational complexity associated with

schemes incorporating the range of variability or rate of change in levels with

time are unwarranted.

1.1 Background

Social surveys have consistently shown that of all the highway impacts, noise

from highways and urban traffic disturbs the public most. Recognition of the

annoyance to the public caused by traffic noise has led Congress to direct

the Secretary of Transporation, through an amendment to Title 23 of the United

States Code, Section 109 (i), to promulgate highway noise standards. The

Federal Highway Administration (FHWA) promulgated noise standards for highways

in 1973, (revised in 1976, 1978 and 1982) in Procedures for Abatement of

Highway Traffic Noise and Construction Noise, 23 CFR 772.

1
During the development of its highway noise standards the FHWA considered the

environmental, social, and economic impacts of various noise levels. Hearing

impairment and the general adverse response to noise exposure were considered

to be the most relevant aspects of human response to highway noise. Based

upon the data base available then it was concluded that community exposures to

traffic noise were not severe enough to induce hearing impairment. However,

the same data base indicated that the most important impact of traffic noise

was on the general adverse response, defined as a combination of several factors

such as speech interference, sleep interference, the desire for quiet, and the

ability to use satisfactorily the telephone, radio and television.

While insufficient information existed then regarding the effects of timevarying noise on people, a large body of data was available on the effects of

steady-state noise exposure on speech communication. Since many of the factors

involved in the general response to noise exposure are related to activity

interference, especially speech communication, the effect of steady-state

noise on speech communication became the basis for selecting highway noise

criteria.

When FHWA promulgated its highway noise criteria it recognized that speech

interference caused by steady-state noise was an insufficient basis for standards

applying to predominantly time-varying noise. Hence, FHWA committed itself to

a future reevaluation of these noise standards as research data on the effects

of time-varying highway noise became available. Accordingly, FHWA requested

participation by the National Bureau of Standards (NBS) in a study designed to

provide important data bases required by FHWA for this reexamination. The

results of this joint FHWA/NBS research are summarized herein.

1.2 Goals of the Study

This research program was designed to (1) identify and quantify the important

physical parameters associated with time-varying noise caused by various

densities of both free-flowing and stop-and-go traffic; (2) investigate,

evaluate, and compare measures and computational procedures for rating timevarying noise either in use or proposed; (3) determine by means of a laboratory

psychoacoustic study which among several time-varying noise ratings best

predicts human response to actual samples of traffic sounds; and, (4) if none of the noise-rating indices adequately predict human response, develop an improved procedure based upon the data obtained in the psychoacoustic study.

1.3 Organization of the Study

In view of the rather large scope of the study the work was organized in a series of discrete phases. First, in order to identify and quantify the

important physical parameters associated with time-varying highway noise,

analog recordings of actual traffic sounds were made at several times of day,

at several sites selected to represent a variety of highways.

2
Second, since traffic noise is often a cause of disturbance in the home, it was felt that, in order to obtain useful data on the effects of time-varying

highway noise on people, it would be desirable to present traffic sounds

to subjects as heard both outdoors and indoors. Hence, the second phase of

the study involved a series of sound pressure measurements obtained

simultaneously indoors and outdoors at several locations at each of several

dwellings. From these data an electronic filter was developed which

simulated the average sound isolation of residential building shells in the

Washington, D.C. area.

Third, in order to identify which aspects of time-varying noise may affect

human response and how these parameters can be incorporated into a noiserating scheme, an in-depth review of the literature dealing with the effects

of time-varying noise on people was undertaken.

Fourth, a psychoacoustic study was conducted to assess the response, as measured in the laboratory, of adult subjects to three-minute samples of

traffic sounds and to evaluate the accuracy of selected noise-rating procedures in predicting these responses.

The major thrust of the FHWA/NBS Study centered upon the temporal aspects of

highway noise. However, in view of the large body of data acquired during

the course of the study and the general tendency to use the A-weighted level to

account for the differential sensitivity of people to various frequency bands,

the relationships among major frequency-weighting schemes and the A-weighted

level were explored through analysis of the data bases acquired during the

first phase of the program.

2. SUMMARY OF THE HIGHWAY NOISE STUDY

The procedures utilized and the data obtained during the course of this program

are fully documented in Refs. 1-5. Only a brief description of each phase of

the work is given below.

2.1 Traffic Noise Data Base (Ref. 1)

Fifteen minutes of analog recordings of actual traffic sounds were made at four

microphone positions at each of seven sites selected to represent a variety of

highways. The criteria used to select the sites, the site characteristics,

and the methods used to obtain and analyze the library of actual traffic

sounds are given in Secs. 2 and 4 of Ref. 1. Complete descriptions of the

sites are given in Appendix A while the data bases are documented fully in

Appendix B and C of Ref. 1.

3
Five of the chosen sites had nominally constant-speed traffic while the other

two corresponded to stop-and-go intersection traffic. During each recording

session all microphones were located 1.2 m above the ground at distances of

7.5, 15, 30, and 60 m from either the nearest lane of traffic along a line

perpendicular to the highway (for constant speed traffic) or at the same distances along a line bisecting the angle formed by the two highways (for

stop-and-go intersection traffic).

A total of 107 traffic recordings was obtained, each lasting 15 minutes.

These were subsequently analyzed in the laboratory so as to yield graphic

plots and digital records of sound pressure levels as a function of time.

These data were themselves extensively analyzed.

During each recording session, video recordings of traffic flow were also made

to count and classify vehicles (i.e., number of automobiles, medium trucks,

and heavy trucks in each traffic direction).

To obtain graphic plots of the A-weighted sound level, the electrical signal

from the tape recorder was fed into a precision sound level meter set for

"fast" A-weighted response. The detected root-mean-square output from the

sound level meter was fed into a graphic level recorder set for DC response and

having a writing speed sufficiently fast to enable the pen to follow closely

the signal from the sound level meter. Figure 1 illustrates the data that were obtained in this manner.

To obtain digital records of sound pressure levels, the signal from the tape

recorder was fed also into a real-time 1/3-octave band analyzer where the

signal was analyzed as A-weighted levels and as 1/ 3-octave band sound pressure

levels for the frequency range having center frequencies from 25 Hz to 16 kHz.

For these analyses the integration time was set to 0.1 s. Outputs from the

analyzer were sent to a minicomputer for format and storage on digital tape.

The digital tapes were processed on the NBS central computer facility after

being edited for questionable runs and/or extraneous noise events (e.g., horns

blowing, shouting, airplanes). The digitized sound levels were exponentially

smoothed to obtain data corresponding closely to the levels that would have

been obtained with a precision sound level meter set for "fast" response.

Using these exponentially-smoothed , digitized l/3-octave band sound pressure

levels, cumulative probability distribution plots of A-weighted sound pressure

levels observed during each recording were obtained. An example of the

distribution plot is shown in Fig. 2.

In addition, the A-weighted sound pressure levels for each 30-s time block and

for the entire 15-minute duration of each recording were tabulated, as were the

levels exceeded 1, 10, 50, 90, and 99 percent of the time, the traffic noise

index (TNI), the standard deviation of levels around the mean value (a),

the equivalent sound level (L ) , the noise pollution level (NPL) , the rate of

0CJ change of levels with time(dL/dt) and two equivalent sound levels incorporating

a correction for the rate of change of levels with time: L ' and L_ . An

eq B

example of these data is shown in Table 1. A definition of each of these

noise descriptors is given in the appendix to this technical summary.

4
-4 1 min

Figure 1. A-weighted sound pressure level time history for the GUDE DR.

site, 16 June 1977, 1600 hrs., 15-m microphone.

5
PROBABILITY

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LEVEL

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Figure 2. Cumulative probability distribution of A-weighted

sound pressure levels for the GUDE DR. site,

16 June 1977, 1600 hrs., 15-m microphone.

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Using the digitized 1/3-octave band sound pressure levels over the frequency

range from 50 Hz to 10 kHz, time-averaged spectra were computed for the levels

exceeded 1, 10, 50, 90, and 99 percent of the time and for the equivalent band

sound pressure levels (L ) for the entire duration of each sample. These data were tabulated and graphed as illustrated in Table 2 and Fig. 3.

Included among the sites selected for inclusion into the study were 3 interstate highways, 2 secondary roads, and 2 intersections. Accordingly, the

data obtained were grouped for further analyses into 3 categories, corresponding

to these types of highway. Table 3 summarizes the traffic conditions prevailing

at the three types of highways during the recording periods.

During the review of the literature dealing with human response to timevarying noise (see Sec. 2.4 below) it was found that the equivalent sound

level (L ) , the level exceeded 10 percent of the time (L^q), the noise

pollution level (NPL) , the traffic noise index (TNI), and two equivalent

sound levels adjusted for the rate of change of levels with time (L^ and L^) were deserving of further investigation. Accordingly, for each of these timevarying noise descriptors, the minimum, mean, and maximum values observed for

each type of highway were computed as a function of distance of the microphone

from the center lane of traffic. The data obtained are summarized in Table 4.

Examples are presented graphically in Figs. 4-6, together with the range of

variations observed at each microphone location.

The major finding of this phase of the FHWA/NBS research program can be seen by

inspection of Table 4, which reveals that, independent of the type of highway

or microphone position, L and behave in a similar manner, with L^q being

typically 2 to 4 dB larger than . In general, L^, L^, and NPL show a slightly more rapid falloff with distance than do L , or L-_. Further, TNI

eq 10 was found to fall off with distance much more rapidly than any of the other

descriptors and yielded a much larger range of values than all other descriptors

included in these analyses.

2.2 Outdoor/ Indoor Noise Isolation (Ref. 2)

In order to determine how outdoor traffic sounds are modified when heard by

listeners located indoors, outdoor-to—indoor noise isolation measurements were conducted at 9 single- family dwellings located in the greater Washington, D.C.,

area. The test house parameters are summarized in Table 5.

Since these measurements were performed to provide the data base required for

developing a house filter for use in the presentation of psychoacoustic

stimuli, emphasis was placed upon obtaining data at probable listener locations.

Hence, the measurements performed differed significantly from either standardized

or proposed procedures where, typically, the emphasis is on determining the

sound insulation of either a building facade or of building elements.

8
FREQUENCY 1/3 OCTAVE BAND LEVEL

LEQ LI L10 L 50 L 90 L 99

50 71o 0 79o 5 74o 5 6 8o 4 63o 7 6 Oo

6

63 71 .5 79. 1 74. 5 69. 5 64 0 8 61o8

80 73.2 81.5 76.5 70.8 66.0 62o 3

100 72c 6 80c 5 75o 7 7 Oo 6 65.9 62.7

125 70.8 79.7 73.1 67.7 63o 3 6 Oo 1 160 69.5 78.6 71.8 66. 7 62.2 5 9c 2

.200 66.6 76.1 69.2 64. 1 60c 0 5 7c 1 250 63.8 73.5 66.5 60.9 57o 0 54o 1 315 61.0 70.7 63.6 57.5 53o 4 5 Oo 7

400 57.6 67.2 60. 4 54. 9 50.9 48c 5

500 54.9 63.6 57.4 52.8 4 9o 6 47o3

630 54.1 62.0 56.4 52.6 49o 7 47o 5

800 54.9 63.0 56.7, 53.4 5 1 o 0 49c 0

1000 58.4 67.3 56.5 53. 0 50o 8 4 8c 8

1250 57. 1 65.4 56.5 52.9 50o 6 4 8c 4

1600 £5.5 64.5 56.2 52.3 49c 9 4 8o 0

2000 54.5 63.8 54.8 50.7 48o 3 46o 6

2500 52.8 62.9 53.6 49.3 46o 7 44o 8

3150 51.1 60.9 52.3 47.5 44o 9 43c 5

4000 49.8 59.0 50.9 45.7 42o 9 oO

5000 46.9 55.7 48.7 44.0 o 0 oO

6300 45.3 54.0 47. 1 42. 8 o 0 oO

8000 44o 0 5 1 o 6 45o 1 oO • 0 • 0

10000 43.7 49.5 42.9 • 0 oO o 0

Table 2. 1/3-octave band spectra for the 355 and Q.O. RD. site,

24 June 1977, 1600 hrs., 15—m microphone, recording

duration of 14.2 min.

9
SITE : GUDE DR.

DATE : 16 JUNE 77

TIME : 1600

MICROPHONE

:

15 M

Figure 3. 1/3-octave band L , L. , L. n , and L cr. spectra for the

eq 1 1U 5U

GUDE DR. site, 16 June 1977, 1600 hrs., 15-m microphone,

recording duration of 14.5 min.

10
Table 3. Summary of traffic conditions for actual-traffic

noise recordings

Type of Highway Interstate Secondary Intersection

Sites (No. Lanes) COMSAT (4)

195(8)

B-W PKWY (4)

RT. 28(2)

GUDE DR. (2)

355 & 355 & SHADY

0 . 0 . GR. (-)RD.(-)

Traffic Parameter Min Mean Max Min Mean Max Min Mean Max

Average Traffic Speed, km/hr 85 90 93 61 67 71 - -

Total Traffic Volume, veh. /hr 1990 3020 4330 660 1010 1430 2760 3680 5380

Percent Automobiles 77.4 91.9 98.6 84.2 90.8 94.6 88.3 93.2 98.1

Percent Medium Trucks 1.0 2.8 7.1 3.2 4.9 6.4 1.7 4.3 6.5

Percent Heavy Trucks 0.0 5.3 15.5 1.6 4.3 9.8 0.2 2.5 5.2

11
Table 4. Summary of six of the descriptors of the A-weighted sound

levels for the actual-traffic noise recordings.

Type of Highway Interstate Secondary Intersection

Sites COMSAT RT 28 355 & SHADY GR.

195 GUDE DR. 355 & Q. 0. rd.

B-W PKWY

Descriptor Mike Min Mean Max Min Mean Max Min Mean Max

7 . 5m 72.1 77.5 82.0 69.3 73.0 76.1 70.1 71.6 73.7

LEQ 15m 65.3 71.1 78.5 62.0 67.1 70.7 65.5 68.6 71.8

30m 58.3 66. 5 72.2 55.3 59.7 62.9 61.4 64.4 67.4

60m 62 . 4* 66.1* 69.1* 51.7 54.1 56.9 58.3 60.5 63.1

7 . 5m 75.9 80.6 85.2 71.1 75.6 79.2 73.0 74.4 76.2

LIU 15m 68.5 74.7 82.4 65.1 69.5 77.2 67.4 71.0 73.9

30m 60.8 69.4 76.0 57.7 62.1 66.5 63.3 66.4 69.6

60m 65.7* 69.4* 72.6* 51.3 55.8 59.3 59.9 62.4 65.5

LEQP

7 . 5m 91.3 96.3 101.2 87.6 91.5 93.9 86.6 88.1 89.7

15m 83.1 88.8 94.0 79.3 84.4 87.7 79.3 84.0 87.8

30m 72.8 81.3 88.2 70.7 74.9 78.1 74.4 79.0 82.9

60m 77.0* 80.6* 83.4* 66.8 68.8 71.9 70.5 74.4 77.7

7 . 5m 112.4 116.8 122.9 107.9 111.3 112.5 105.1 107.3 109.7

LB 15m 100.3 107.6 115.3 97.7 102.7 105.9 95.5 102.8 107.1

30m 89-6 97-4 105.8 88.6 92.5 95.2 90.1 97.2 102.2

60m 92.7* 95.6* 98.4* 82.2 85.8 89.9 84.1 90.8 95.8

7 . 5m 89.2 93.6 102.6 88.6 93.5 100.9 79.7 82.5 84.1

LNP 15m 77.2 84.9 96.8 79.2 84.9 90.1 72.1 78.4 82.3

30m 67.9 76.9 87.9 68.0 72.8 77.6 66.9 72.9 77.3

60m 73.1* 76.6* 80.3* 61.1 65.0 71.4 62.8 67.7 72.2

7 . 5m 81.4 97.5 120.7 93.6 106.1 127.8 70.7 75.2 78.0

TNT 15m 68.9 83.7 110.6 78.0 91.7 106.1 54.8 67.7 74.7

30m 52.2 69.8 94.1 67.7 69.9 83.7 47.5 59.0 65.6

60m 61.3* 70.7* 77.8* 47.4 54.8 59.3 41.4 51.2 59.5

* The data for Interstate highways do not include recordings at the 60-m

microphone position for the B-W PKWY site.

12
Figure 4. Variation of observed values of L , L

f , and L_ with

eq eq B

distance for interstate and secondary highways and for

intersections. The solid symbols represent the average

ratings over all recordings at all sites of a given type.

The error bars represent the ranges of the ratings.

13
Figure 5. Variation of observed values of and NPL with distance for

interstate and secondary highways and for intersections.

14
Figure 6. Variation of observed values of TNI with distance for

interstate and secondary highways and for intersections.

15
Table

5.

Summary

of

test

house

parameters.

4J

oj 0) o 0) c u £ o i-H o CO <r in <r in U CO 'w' rH CM VO CM i-H i-H i-H CM rH

(A •H o Q H .s /

0)E /—N e 3 co o rH g

m M3" <r CO CM i-H CO 00 o O V-/ in v£5 ID m MT r- m 00 <r

cu >9 rH s o 03 C TJ •H o c 4J 0) i-H oj i-H 0) i-H 0) rH

4J •H Vi c rH c i-H e i-H e rH

CO CO o 3 o 3 o 3 o 3

Pk z z pH z Eh z Ph

rH

03 /^s

4J CM kj- vO CO <r 00 o vOm

m o e • H V-/ CO CO CO CO co m Mf vO m

03 01 /'—s 0) XJ CM rH rH vO rH U •H g o o o o • • • • • < C/5 , v-/ rH CM rH CM rH 9

T3e

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m

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(A

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•H 4Juu

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Vi c QJ c Q> c 0) z c OJ c

•U

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/-N /~s

<0| cfl | cO | U i-> /'“'s 4J

C z rC >> fs Z o oo 00 r-H i-H 00

•H

V -H Vi

V -r-l Vi 3 V c M -H

U 0) 0) <U OJ CD 0)

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CJ <U

X 0) OJ Z 01 0) 0) Z 3 c c C C vi C VI c

Vi 0) r—1

OJ 0) iH <U

C 0)

C 0) iH

U > CO > > CO > O > O > CO (A •H •H M u •H c p*: v) P>E .H P»E u 0) Eh 01 PP Eh P»i VI a) a) o o V O rH u V C E O O M E £ u •rH 0J •H 3 •H oJ o c 03 ^ c •H 03 03 cd V Ph Vi Eh V P-I vi O Vi VI o M Z Vi Vi pa pq ^ pa ^ CO fa pa v' « Ph Ph

<u

co • 3 O O Z

PC

16

To

Top

of

Window
The major difference between the procedure utilized in this study and those

normally used is that in the present study interior microphone positions were

deliberately chosen so as to yield the spatial averaged mean-square pressure

over probable listener positions rather than at locations chosen to yield the

average over the entire volume of the test room. Accordingly, a sound

isolation metric dubbed "Noise Intrusion Reduction" (NIR) was defined to avoid

confusion with current definitions of sound isolation and sound insulation.

By definition, the Noise Intrusion Reduction, NIR, is the difference between

the outdoor time-varying sound pressure level and the sound pressure level at

a listener position or averaged over a number of listener positions in the

receiving room. Hence, the NIR does not include terms to adjust for either

the size of the partition or the receiving room absorption.

Details covering the measurement procedures used in this study can be found

in Secs. 2 and 3 of Ref. 2. Suffice it to say here that, at each of the

selected houses, simultaneous analog tape recordings were obtained of the sound

pressure at seven microphone positions, three located outdoors and four indoors,

while a small NBS truck was driven past the test house at a nominal speed of

48 km/hr (30 mph) . Since the truck produced insufficient signal indoors at

high frequencies, the truck spectrum was supplemented with "pink noise" broadcast

through loudspeakers. The loudspeakers were placed on the van step on the

opposite side of the vehicle from the driver. In this position the loudspeakers

were approximately 0.75 m above the pavement. With the addition of the supplemental pink noise, sufficient interior noise was obtained to determine the noise

isolation provided by the building shells over the frequency range from 50 Hz

to A k H z

*

The exterior and interior analog sound pressure recordings for each of the nine

test houses were reduced to 1/3-octave band sound pressure levels according to

three processing methods. The first method was designed to produce 1/3-octave

band sound pressure level time histories for the individual vehicle passbys.

The second method yielded the maximum sound pressure level occuring in each

1/3-octave band during an individual vehicle passby. The third method was designed to yield the average 1/3-octave band levels obtained by averaging

the squared sound pressure over an 8-second interval during each passby. Th s was done so as to allow for the computation of the sound exposure level (SET)

•s.inu e.ua pas-.bv s'- oar1

, microphone position.

The vhre. sc: of data -bLained in the manner discussed above were used to

derive for each building facade the NIR values in each 1/ 3-octave band over the

range extending from 31.5 Hz to 4 kHz. The resulting data are given in Appendices

B, C and D of Ref. 2. A graphical illustration of the type of data obtained

using each of the processing methods is illustrated here in Fig. 7.

The data presented in Appendices B, C and D of Ref. 2 were subjected to intense

scrutiny in order to determine which among the three sets should be utilized to

derive the desired house filter. The results of these analyses are discussed

in Sec. 4 of Ref. 2. Suffice it to say here that the NIR values obtained

using the maximum sound pressure level in each 1/ 3-octave band during each

passby yielded the best data from the point of view of run-to-run consistency

and maximum signal-to-noise ratio. For these reasons further analyses were carried out using the data obtained by this method.

17
BAND CENTER FREQUENCY (Hz]

'igure 7. Noise Intrusion Reductions, for the three different data

sets, at Test House No. 6.

Data Set No. 1. Computed from simultaneous 1/3-octave band

levels at the time of maximum interior

A-weighted level.

Data Set No. 2. Computed from the maximum 1/3-octave band

levels, regardless of when they occurred.

Data Set No. 3. Computed from 1/3-octave band sound exposure

levels.

18
The average NIR values in each 1/3-octave band for the set of all nine houses were

computed. Those data are presented in Fig. 8, together with the range of NIR

values in each 1/3-octave band for average values for individual houses and the

range for individual microphone positions for all nine houses. Inspection of

Fig. 8 shows that the range in the average NIR values for individual houses is

less than 10 dB in all 1/3-octave bands except those centered at 40, 100, and

125 Hz.

The NIR values obtained in this study were compared to noise isolation data

published in the literature. These comparisons revealed that the data obtained

compared favorably to published data for constructions located in cold

climates. Neither the data obtained here nor those published for cold climates

compared favorably to noise isolation data published for construction in warm

climates. Hence, the electronic house filter derived in the present study,

according to procedures described in Appendix E of Ref. 2, is more representative

of the Noise Intrusion Reduction provided by dwellings in colder climates than

in warmer climates. The frequency response of this filter is shown in Fig. 9.

Inspection of Figs. 8 and 9 shows that the frequency response of the electronic

filter over the frequency range extending from 50 Hz to 4 kHz simulated the

average NIR values for the aine test houses included in the study, and had a nominally flat frequency response above and below these frequencies.

2.3 Effects of Time-Varying Noise on Annoyance

One of the major goals of the FHWA/NBS study was to examine, evaluate, and

compare measures and computational procedures for rating time-varying noise

in terms that are relevant to human response. Accordingly, while the physical

measurement program was underway, an in-depth review of the literature dealing

with human response to time-varying noise was undertaken, noise rating

procedures were identified, and a psychoacoustic study was designed. The

following sections outline the major findings of this literature review and

the results of the psychoacoustic study.

2.3.1 Literature Review (Ref. 3)

Over the last 30 years or so, numerous studies of the effects of environmental

noise on people have been conducted in this country and abroad. These studies

are reviewed in detail in Ref. 3; only major findings are summarized here.

Two main approaches have been utilized to achieve a better understanding of

human response to time-varying environmental noise. The first approach has

involved field investigations in which, typically, the environmental noise

levels are measured, on a continuous or intermittent basis, throughout a community and a social survey is conducted to assess the effects of the noise

on the impacted population. The second approach has been to investigate under

laboratory conditions the effects of a particular environmental noise parameter

(e.g. number and/or duration of discernable noise events, intermittency) on a specific human response such as speech interference and annoyance.

Most social surveys have resulted from public expression of dissatisfaction with

either the introduction of a new noise source or system in the environment or as a result of a significant increase in the noise producted by an existing

system. Hence, most social surveys were designed to assess the annoyance and/or

19
31.5 63 125 250 500 1000 2000 4000 6000

BAND CENTER FREQUENCY |Hz]

Average and range of Noise Intrusion Reduction values fo . all nine test houses.

20
BAND CENTER FREQUENCY (Hz]

Figure 9 , Outdoor-to-indoor noise reduction simulated by an electronic house filter.
community response produced by a specific noise source. The result has been

the development of diverse methods for expressing the relationship between human

response and the physical attributes of the noise. During the last decade

researchers have become more aware of the need to develop a unified noiserating index that would apply to all environmental noises independently of the

noise source.

A common result of social surveys is that people exposed to noise in their homes

show a generalized adverse response which increases with increasing noise

exposures. This generalized response is complex and involves a combination of

factors including speech interference, sleep interference, a frustrated desire

for quiet, and inability tp use telephone, radio, and television. Thus, one major

factor contributing to annoyance frequently involves activity interference.

Other factors involved include socio-economic parameters (e.g., sex, age,

education, income bracket) as well as other ill-defined parameters.

In view of the complexity of human response to time-varying environmental noise,

it is not suprising that while the average response of homogeneous groups of

people can be predicted reasonably well, individual responses cannot. Social

survey data consistantly show that in the aggregate the average response of

groups of people is highly correlated with a number of noise-rating indices,

with correlation coefficients often greater than 0.9. These high correlations

arise in part because all noise-rating indices increase with increasing

sound pressure levels. On the other hand, individual response scores are consistently unpredic • '* t correlation coefficients between individual

scores and noise exposure levels typically being about 0.4.

Several attempts have been made to explore the relationship be ' i. individual

personality traits and noise induced annoyance; however, the results of these

studies are unclear and many questions remain unanswered. For example, while

social survey data show that approximately 10 to 15 percent of the population

is always bothered by noise, no matter how quiet it is, a similar percentage

of people are never annoyed no matter how loud the environment is. No

explanation of this phenomenon has been forthcoming. Some researchers have

argued that the relationship between annoyance and noise exposure is modified

by intervening variables such as fear and misfeasance while others using the same data base have not been able to show such intervention.

Another major social survey finding is that in many instances people are able

to identify, when interviewed, the specific noise that annoys them most. However, the same data also show that the annoyance produced by a specific noise

source, such as an airport, is influenced by the presence of another noise source,

such as a freeway. The relationship between the two noise sources or systems

and annoyance is complex and dependent upon several factors such as the relative

levels of the two sources, and the intermittency of one relative to the other.

Moreover, the relationship between annoyance and a particular noise source is

influenced by the time of day during which the exposure occurs. For example,

there is a general consensus among researchers that noise events occurring at

night are more annoying than the same events occurring during the daytime. However,

recent findings suggest that people are more annoyed with events occurring in the

evening rather than at night. Exposures to noise during evening hours have not

been studied systematically and most noise-rating indices do not account for

evening hours.

22
Although considerable data have been gathered through field investigations, all

that can be said with any degree of confidence is that there exists a relationship between community noise exposure and annoyance. However, this relationship

depends partly on the character of the noise and partly on other-ill defined

parameters that may or may not bear a relationship to the noise. Much remains to

be learned about the etiology of noise-induced adverse response. This is perhaps

the reason why, during the late 1960's and the 1970's, more and more researchers

have turned toward the laboratory for answers.

Laboratory studies have been used to investigate the effects of human response of

such parameters as the number of noise events discernible in a background

noise, the variability in the noise levels during the period of observation,

the rate of interruption in the noise exposure, the interaction of various

noise sources as, for example, the superimposition of aircraft noise on traffic

noise. Again the primary purpose of these studies was to gain sufficient

insight into the etiology of noise-induced annoyance in order to develop noiserating indices for predicting human response to noise from measurable physical

parameters of the noise. The major findings of these studies are described in

detail in Ref. 3 and n i c only summarized below.

The adverse response to time-varying noise exposure, as measured in the laboratory,

is not only dependent upon the sound pressure level but also upon other

physical parameters of the noise, especially the number of discrete noise events

and intermittency . Unfortunately, the relationship between measured annoyance

and either interruption rate or number of events is complex and nonmonotonic.

It appears that below a certain "threshold", in either the rate of interruption

or the number of discernible noise events, the adverse response to noise is

unaffected by these parameters. However, when the rate of interruption and/or

number of events reaches a certain level, annoyance appears to increase with

the rate of interruption and/or the number of events until an upper threshold

is reached. Above this threshold further increases in either interruption rate

and/or number of events do not influence annoyance or, sometimes, even result in

a decrease in annoyance. Within the range where increases in the interruption

rate or the number of discernible events contribute to increased annoyance, the

relationships between these factors and annoyance vary from study to study and

among types of noise sources.

Although some researchers argue strongly that variability in the noise levels

during the observation period contributes to annoyance, the data examined

showed that in many instances variability per se had little effect on measured

annoyance. In some instances the more variable noises were found to be less

annoying than steady-state noises presented at the same average level. Further,

when the offending noises originate from two different and distinct systems,

level-dependent interactions between the resulting noises occur and this in

turn affects the measured annoyance in a complex manner that varies from study to

study.

While laboratory studies have been very useful in identifying those parameters

of time-varying noise that potentially affect annoyance, the relative contributions

of these parameters to annoyance are unclear; accordingly, the development of

rating schemes that adequately account for these parameters has not been forthcoming. Nevertheless, during the last 10 years, the proliferation of

environmental noise indices has been recognized as a major impediment to the

23
development of meaningful noise control and abatement programs since, in the absence of a unified metric to measure all noise exposures, environmental

noise goals are difficult to express. Thus, the shift in recent years has

been toward reanalyses of existing data bases with the aim of arriving at a general environmental noise descriptor. These efforts were also reviewed in

Ref. 3.

Despite the fact that numerous noise indices have been put forth for characterizing

environment.^ u . k-e, nk . amseusus has been reached as to wi'uch besi. pieuiccs

human response to noise. Moreover, careful examination of these various indices

reveals that for all practical purposes the large number of indices can

be grouped into three general categories. The first category is predicated

upon the assumption that exposure to the same equivalent sound levels, L , over a fixed period of time will produce equivalent adverse human response.

The second category of noise indices is predicated upon the assumption that

while the general response to time-varying noise increases with increasing

sound levels, it also is affected by the extent of the variability in the

sound levels during the period of observation. For some of the indices that

fall in this category (e.g., NPL) the equivalent sound level (L ) is adjusted

eq

by adding a measure of the extent of variability in sound levels. Other

indices are expressed in terms of some statistical description of the

observed sound levels (e.g., and TNI).

The third category is based upon the assumption that while the adverse response

to time-varying noise increases with the equivalent sound level, people’s

sensitivity to how rapidly the levels change during the observation period

is important and must be incorporated into the noise-rating. Indices falling

in this category, typically, adjust the equivalent sound level (L e^) by adding

a term that is a function of the rate of change of levels with time (dL/dt)

.

Each of the general noise rating categories discussed above emphasizes different

aspects of time-varying noise. Thus, predictions of human response given by each

category of descriptors vary. Further, as one moves from the first category to

the last, both the physical measurement and computational procedures required

significantly increase in complexity. In view of the lack of firm evidence for

adopting one scheme over another it was decided that the psychoacoustic study

should be designed to assess how the various schemes predict human response under

controlled conditions.

2.3.2 Laboratory Study (Ref. 4)

Upon completion of the literature survey, six noise-rating procedures were

selected from among the three general categories of noise descriptors and a psychoacoustic study was designed to assess which among these descriptors best

predicts human response to time-varying noise. Included among the noiserating procedures tested were the equivalent sound level (L^), the level

exceeded 10 percent of the time (L^q)

,

the traffic noise index (TNI) , the noise

pollution level (NPL) , and two indices incorporating a measure of the rate of

change of level with time (L„ and L ’). Details concerning this study are

B eq

given in Ref. 4; only a brief review is given below.

24
Twenty-eight audiologically normal adult subjects were required to judge both

the annoyance caused by and the acceptability of 3-minute exposures to 12

samples of recorded sounds, presented as recorded (but with selected frequencyindependent attenuations) and as modified by the house filter described above.

The experiment was conducted in the NBS realistic listening room. Annoyance

judgments were obtained through the use of a magnitude estimation technique.

Specifically, subjects were required to indicate how annoying traffic sounds

were by assigning a number from 1 to 10 after hearing each stimulus, with

smaller numbers being assigned to the less annoying sounds. Acceptability

judgments were obtained by having the subjects check on a scoring sheet a box entitled either "acceptable" or "unacceptable".

In the course of the experiment each subject was required to judge 24 acoustic

stimuli 4 times, yielding a total of 96 annoyance and 96 acceptability judgments

per subject. From the data thus obtained, annoyance scores for each of the

stimuli were computed. A one-way analysis of variance was performed and

disclosed that the 3-minute segments of traffic noise were perceived by the

subjects as being significantly different from one another. This analysis

also indicated that 73 percent of the variance observed in the annoyance

scores was attributable to the stimuli themselves.

Moreover, since the main purpose of the experiment was to assess how each

selected environmental noise-rating index predicted the measured annoyance,

the A-weighted L , L,~, L L_, NPL, and TNI for each of the 24 three-minute

eq 10 eq B

stimuli were computed from physical analyses of these traffic sounds as playedback into the listening room. The results of these computations are shown in

Table 6.

Regression analyses were performed to assess how well each noise

related with the measured annoyance. Linear regression parameters for each

noise rating are documented in Ref. 4 and are summarized here in Table 7. Inspection of Table 7 shows that the product-moment correlations (r) were high

in all cases, rating from 0.99 to 0.93, with TNI showing a slightly smaller

value (r “ 0.83)

.

Further analyses using techniques developed for interdependent correlation

coefficients were carried out. These revealed that while all the noise-rating

procedures predicted annoyance scores well, the accuracy of the predictions

varied. Specifically, L , L^q, and L^' accounted for 96 to 98 percent of the

variance in the annoyance ratings while NPL and L_. accounted for 86 to 90

B

percent, and TNI did worst with only 69 percent of the variance in the

annoyance scores accounted for. The relationships among the various noiseratings were also very high, as summarized in Table 8 which shows the correlation

coefficients among the various noise indices.

The second set of judgments, that is the acceptability judgments, were analvzed

independently from the annoyance judgments using similar techniques. The data

obtained revealed that so long as the equivalent sound level, L , was at or

eq*

below 50 dB over half of the subjects found the stimuli "always acceptable";

however, stimuli having L values greater than about 55 dB were judged as

25
1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

Computed A-weighted noise rating values for the three-minute

time-varying highway noise stimuli as presented to the subjects

in the listening room.

L

eq

L

10

L

' eq

NPL TNI

65.6 69.0 80.8 77.0 95.7 73.7

43.6 46.2 56.4 50.1 70.1 36.7

70.0 73.0 84.5 79.4 98.7 72.9

45.9 48.2 58.9 52.3 72.1 38.3

71.7 74.8 90.3 85.8 108.8 86.9

51.5 55.5 70.6 63.9 89.1 60.3

58.4 61.5 76.4 74.8 96.3 79.7

45.6 47.8 62.5 55.4 82.5 44.8

63.3 65.1 79.9 73.7 99.7 63.8

52.0 53.8 68.4 61.7 88.0 50.0

63.9 64.4 80.5 74.0 102.5 60.1

48.3 48.7 64.6 56.7 85.9 38.4

61.1 62.7 76.3 68.2 94.7 51.9

45.8 46.8 59.5 50.7 75 0 5 32.3

58.7 61.6 76.5 77.6 96.1 89.6

46.4 48.3 63.0 57.4 82.8 48.0

56.1 58.6 71.7 66.8 91.9 60.4

46.5 48.7 61.8 55.3 81.8 43.4

56.0 59.2 72.2 68.8 89.5 68.4

44.4 46.6 59.5 52.2 77.0 38o 8

56.8 59.2 71.1 65.0 85.5 54.5

40.4 41.3 51.7 43.4 63.0 19.3

68.6 72.9 86.0 85.2 104.5 94.7

55.7 60.2 72.9 71.2 91.8 78.4
Table 7. Results of linear regression analyses between annoyance rating

scores and noise indices.

L

eq

r-1

h* o L

' eq

NPL l

b

TNI

product moment

correlation (r)

0.99 0.98 0.98 0.95 0.93 0.83

amount of variance

accounted for (r2)

0.98 0.98 0.96 0.90 0.86 0.69

Table 8. Matrix of correlations between noise indices.

^eq L10

T • Leq NPL lB TNI

Leq — 0.99 0.99 0.96 0.93 0.84

L10 — 0.99 0.97 0.93 0.88

Leq* — 0.98 0.97 0.87

NPL — 0.96 0.95

lB — 0.87

TNI —

27
"always unacceptable" by over half the subjects. Accordingly, a demarcation

•'nr between two categori r* either acceptable or urn- *e. i at e traffic

sounds, as heard indoors in the laboratory, occurred somewhere between L = 50 and L = 55 dB. eq

eq

The most si g

f i cant finding of the psychoacoust Lc study was that. .

' *r the type

of noise studied here, the simpler noise measurement and rating schemes such as L and correlate very well with annoyance as measured in the laboratory.

This suggests that within the constraints of this experiment the most important

factor contributing to both annoyance and acceptability is by far the sound

pressure level. Further, since both L and L,_ are highly correlated with

eq 10

annoyance, and since all other rating schemes studied are highly correlated

with each other and with L and L.^, it appears that the measurement and

computational difficulties associated with the more complex schemes are unwarranted.

2.4 Relationships Among Frequency Weightings (Ref . 5)

A series of calculations was performed to ascertain how well one frequencyweighted rating, such as a weighted sound level, a loudness level, or the

perceived noise level, may be predicted from another such rating. A total of

103 average sound level spectra selected from the recordings discussed above

in Section 2.1 were used in these computations. It was found that knowing a single frequency rating, such as the A-weighted sound level, enables one to

predict other outdoor frequency ratings with a standard deviation of the order

of 1 to 2 dB. If, in addition, traffic speed, mix and the distance to the

highway are taken into account, these standard deviations can be reduced to

0.5 to 1 dB, depending upon the particular frequency noise rating of interest.

Equations are given in Ref. 5 for predicting one rating from another; the

associated standard deviations are presented as a measure of how well any

given rating can be predicted from a single measured, or otherwise known,

noise rating. It is concluded that the choice of a frequency-weighting procedure is not critical in conjunction with highway noise since one descriptor

can be predicted from another with a small statistical uncertainty. Thus,

if human response criteria, or stimulus-response relationships, have been

developed in terms of one frequency-weighting procedure, these criteria may

be translated into equivalent criteria expressed in terms of a frequency metric

that is easier to measure or predict.

28
3. REFERENCES

1. Flynn, D.R., Vorhees, C.R. and Yaniv, S.L. Highway Noise Criteria Study:

Traffic Noise Data Base, NBS Technical Note 1113-1 (National Bureau of

Standards, Washington, D.C., 1980).

2. Donovan, P.R., Flynn, D.R., and Yaniv, S.L., Highway Noise Criteria

Study: Outdoor /Indoor Noise Isolation, NBS Technical Note 1113-2 (National

Bureau of Standards, Washington, D.C., 1980).

3. Yaniv, S.L.

.

Bauer, J.W., Flynn, D.R.

,

and Danner W.F., Effects of TimeVarying Noise on Annoyance: A Review, NBSIR 81-2377 (National Bureau

of Standards j Washington, D.C. 1981).

4. Yaniv, S.L., Danner W.F., and Bauer, J.W., Measurement and Prediction

of Annoyance Caused by Time-Varying Highway Noise, Journal of the

Acoustical Society of America 72^, 200-207 (1982) .

5. Flynn, D.R. , and Yaniv, S.L., Highway Noise Criteria Study*. Relationship

Among Frequency Rating Procedures, NBS Technical Note 1113-3 (National

Bureau of Standards, Washington D.C., 1982).

29
APPENDIX. DEFINITIONS OF TIME-VARYING NOISE DESCRIPTORS

This appendix contains mathematical definitions of time-varying noise

descriptors discussed in the main body of this technical summary. In

all instances the term L(t) denotes the A-weighted sound level as a

function of time.

1. L (e.g. L, , L1rt , Lnn , Lnr.) is the A-weighted sound level re n 1 10 50 90 99

20 liPa in decibels, exceeded n percent of the time, where

n = 1, 10, 50

2 . Traffic Noise Index (TNI)

TNI - L90+ 4(L

10 - L

90> - 30.

3. Equivalent Sound Level )

L

eq

10 log

10

L(t)/10

dt , ( 2 )

where T is the total time of observation and L(t) is the A-weighted

sound level at time t.

30
4. Noise Pollution Level (NPL)

NPL = L + ka , (3)

eq

where L is as in Eq. (2), O is the standard deviation of the population

eq

of A-weighted sound levels observed during the period of observation,

and k is an empirical constant selected to be 2.56.

5. L

' eq

L

' eq

f(a’). (4)

where L is as in Eq. (2) and f (o') is a function of the root-meansquare value of dL/dt, the rate of change of sound level with time.

That is.

o’ (dL/dt) 2dt

l/2

* (5)

where T is the observation time, and

f(a’) = A l°g

10 (1 + Ba') ( 6 )

where A = 10 and B = 15 s

31
( 7 )

6. L

b

where k is a constant, T is the time of observation, and

p (t) - \ g(t-T) P (T)dt , (8)

J mmco

in which (t) = 10 and g i s the Fourier transform of a

weighting function G(w).

For G(oo) = 1, L = L . B eq

For G(oo) = 1 + ioog.

(dL/dt)

2JlO

L(t)/k

dt , (Eq. 10)

where T* = (ft/2k In 10) is a time constant which determines the

limit beyond which rates of change of the sound level, dL/dt, -

contribute significantly to the noise index value. For this

study T* was set equal to 15 s.

32
NBS-114A irev. 2-80

U.S. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET (See instructions)

1. PUBLICATION OR

REPORT NO.

2. Performing Organ. Report No. 3. Publication Date

NBSIR 82-2610 October 1982

4. TITLE AND SUBTITLE

Highway Noise Criteria Study: Executive Summary

5. AUTHOR(S)

Simone L. Yaniv and Daniel R. Flynn

6. PERFORMING ORGANIZATION (If joint or other than NBS. see in struction s) 7. Contract/Grant No. NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE ». Type of Report & Period Covered

WASHINGTON, D.C. 20234

9. SPONSORING ORGANIZATION NAME AND COMPLETE ADDRESS (Street. City. State. ZIP)

National Engineering Laboratory

10. SUPPLEMENTARY NOTES

Document describes a computer program; SF-185, FIPS Software Summary, is attached.

11. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant

bibliography or literature survey, mention it here)

This report summarizes a multifaceted research program carried out by the acoustics

staff of the National Bureau of Standards at the request of the Federal Highway

Administration. The program was designed to (1) identify and quantify the important

physical parameters associated with time-varying highway noise caused by various

densities of both free-flowing and stop-and-go traffic conditions; (2) investigate

evaluate and compare measures and computational procedures for rating time-varying

noise in terms that are relevant to human response; and (3) determine by means of a laboratory study which among several time-varying rating schemes best predicts

acceptability and annoyance caused by traffic noise as heard both outdoors and

indoors. The results of this program are briefly described and the implications of

the major findings discussed.

12. KEY WORDS (Six to twelve entries ; alphabetical order; capitalize only proper names; and separate key words by semicolon s) Acoustics; general adverse response to noise; noise measurement; Sound.

13. AVAILABILITY 14. NO. OF

PRINTED PAGES

[_Xj Unl imited

| | For Official Distribution. Do Not Release to NTIS

[~n Order From Superintendent of Documents, U.S. Government Printing Office, Washington, D.C.

20402.

38

15. Price

Order From National Technical Information Service (NTIS), Springfield, VA. 22161 $7.50

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