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The Audible Landscape

Appendix B. Noise Effects, Measures, Standards, and Predictors

cartoon drawing of a man's face

This appendix contains brief discussions on the effects of noise on human life and economics, a definition of the noise measures and descriptors used in this manual, a review of certain Federal noise standards, and a listing of three recent noise level prediction techniques. The issues of noise costs, noise prediction and desirable noise levels are complex and controversial. These pages do not attempt a comprehensive analysis of these topics, nor do they advocate one particular standard or predictor. Rather, they are solely intended to provide an introductory background to aid in the use of this manual.

The Effects of Noise

The effects of noise on health are both physiological and psychological, though primarily psychological. Physiologically, excessive noise is capable of producing hearing loss, however it seems unlikely that many people have suffered from highway generated noise in this way.1 Psychologically, the affects are more widespread:

As of yet, no one has been able to calculate the dollar cost of noise, but knowledgeable people think it is high.3 The areas which highway noise affects economically are a) property values, b) impaired health, and c) lowered working efficiency. Property values have been the area of greatest concern because this is where financial impacts are most immediately felt and clearly distinguishable. Although studies have not provided conclusive evidence that highway noise reduces property values, there are strong indications that it does when the property use is incompatible with the highway, as in the case of many residential areas.4 Other economic impacts which should be considered (although difficult to quantify), are those due to impaired health and lowered working efficiency.

Noise Measures and Descriptors

Sound is transmitted as rapid changes in air pressure which can be detected by our ears or by a sound meter. Acoustically, we do not usually measure air pressure changes in linear terms such as pounds per square inch or dynes per square centimeter. If we did, we would find ourselves using an astronomical range of numbers to describe the wide range of audible sounds. Therefore we compress the entire range of audible sounds into a logarithmic scale which has the added advantage of corresponding well to the Human ear's sensitivity to sound. The unit Of measurement is called the decibel (dB).5 The meaning of the dB scale can best be seen from a comparison of common sounds with their dB levels. (See Figure A-16)

It should be remembered that logarithmic scales are not additive. That is, the combination of two 70 dB noise sources does not result in 140 dB; rather, the result is approximately 73 dB.

150 Jet take off (at close range on the ground)
130 Machine gun, riveting machine
120 Thunderclap
117 jet plane (at passenger ramp)
107 Loud power mower
94 Pneumatic jackhammer
90 Sports car, truck, shouted conversation
50-60 Normal conversation
50 Quiet street
40 Quiet room
0 Threshold of Audibility

A-16 Typical dB Readings of Common Sounds1
1 Harold W. Bredin, "City Noise: Designers Can Restore Quiet, at a Price," Product Engineering, November 18, 1968, p. 29.

1W. Dixon Ward, "Effects of Noise on Hearing Thresholds," Noise as a Public Health Hazard, ASHA Reports 4 (The American Speech and Hearing Association, Washington, D.C., Feb. 1969), pp. 40-47.

Federal Highway Administration, Final Environmental Impact Statement Pursuant to Section 102 (2) (C), P.L. 91 -100 - Noise Standards and Procedures (November 1972), pp. 183-186.

2 The Administrator of the Environmental Protection Agency, Report to the President and Congress on Noise, 92nd Congress - 2nd Session, Document No. 92-93, (Washington, D.C.: Government Printing Office, 1972), p.xxii.

3Environmental Protection Agency, The Economic Impact of Noise, (Washington, D.C., U.S. Government Printing Off ice, #TID 300.14, December 31,1971), pp. 39-45.

4Department of California Highway Patrol, Passenger Car Noise Survey, (Sacramento, January 1970.)
Robin M. Towne and Associates, Inc., An Investigation of the Effect of Freeway Traffic Noise on Apartment Rents, prepared for the Oregon State Highway Commission and the United States Department of Commerce, Bureau of Public Roads, October 1961.

5 The reference level for this scale is the zero dB pressure of 0.0002 dyn/cm2.

Noise Measures

Because we are interested in human reaction to noise, it is important that a meter measures noise in the same way that humans perceive it. To the human ear, loudness is not only a function of sound intensity, but also of sound frequency. Higher frequency sounds tend to seem louder to people than lower frequency sounds. Therefore, sound level meters are often equipped with weighting networks which give more weight to higher frequency sounds. There are three different weighting networks, designated as A, B and C, which give varying degrees of weight to high frequency sounds. Highway generated noise is usually measured with the A-weighted network. The readings taken on the meter are recorded in A-weighted decibels (dBA).

In measuring noise which fluctuates, such as traffic noise, it is necessary to consider some average of noise level readings taken over time. In the case of highway noise measurement, it is important that this "average" correlates well with human annoyance to noise. To obtain a meaningful measure of traffic noise, readings can be taken periodically over a period of several hours, and a selected percentile level can be used. Three commonly used noise level descriptors are:
L1O - The noise level exceeded 10% of the time
L50 - The noise level exceeded 50% of the time
L90 - The noise level exceeded 90% of the time

The L1O noise level is an indicator of the noisiest portion of highway traffic, while L5O and L1O respectively represent the average and quietest portions. Because annoyance seems to be more a function of the loudest of the noisiest vehicles, e.g., trucks, the L1O descriptor correlates best with annoyance.

Highway Generated Noise Standards

Using the scales and measures described above, various studies have been done to determine noise levels which are compatible with existing land uses.1 Based on these studies, various government agencies have established compatible noise levels for regulatory purposes. Of particular interest are the noise standards set by the U.S. Department of Transportation's Federal Highway Administration to regulate the design of highways passing through developed areas, and by the U.S. Department of Housing and Urban Development to regulate land use around existing and proposed highways.2

FHWA Standards

Presented here are the noise standards issued by the Federal Highway Administration for use by state and Federal highway agencies in the planning and design of highways:

Design Noise Level/Land Use Relationships3

Land Use Category Design Noise Level-L10 Description of Land Use Category
A 60dBA (Exterior) Tracts of lands in which serenity and quiet are of extraordinary significance and serve an important public need, and where the preservation of those qualities is essential if the area is to continue to serve its intended purpose. Such areas could include amphitheaters, particular parks or portions of parks, or open spaces which are dedicated or recognized by appropriate local officials for activities requiring special qualities of serenity and quiet.
B 70dBA (Exterior) Residences, motels, hotels, public meeting rooms, schools, churches, libraries, hospitals, picnic areas, recreation areas, playgrounds, active sports areas, and parks.
C 75dBA (Exterior) Developed lands, properties or activities not included in categories A and B above.
D - For requirements on undeveloped lands see paragraphs 5a(5) and (6), this PPM.
E 55dBA (Interior) Residences, motels, hotels, public meeting rooms, schools, churches, libraries, hospitals and auditoriums.

1 e.g., The Wilson Committee, Noise - Final Report of the Committee on the Problem of Noise (HMSO, London, 1963); Elizabeth Cuadra and Dale R. Beland, "Rationale for the Comprehensive Control of Urban Noise," paper presented at 16th annual meeting of the Institute of Environmental Science, "The Environmental Challenge of the Seventies,"(Boston, Massachusetts, April, 1970) pp. 12-17; and Highway Research Board, National Cooperative Highway Research Program Report 78, Highway Noise Measurement, Simulation and Mixed Reaction. National Academy of Sciences: National Academy of Engineering, 1969.

2 In addition, the U.S. Environmental Protection Agency regulates vehicle noise emissions.

3 U.S. Department of Transportation, Federal Highway Administration, Policy and Procedure Memorandum 90-2, Noise Standards and Procedures (February 8,1973).

Noise Standards

These levels represent a compromise between what is desirable and what is achievable; hence, local officials may want to strive for lower levels in controlling compatible land use development1.

HUD Noise Standards

In 1971, the Department of Housing and Urban Development adopted noise standards for use by builders of Federally funded housing;2

HUD Noise Level Criteria

Exterior
discretionary - normally acceptable 65dBA-L33

(not to be exceeded more than 8 out of 24 hrs.)

clearly acceptable 45dBA-L2

(not to be exceeded more than 30 min. out of 24 hrs.)

Interior
clearly acceptable 45dBA-L33

(not to be exceeded more than 8 out of 24 hrs.)

55dBA-L4

(not to be exceeded more than 1 out of 24 hrs.)

night: 45dBA-L6

(not to be exceeded more than 30 min. out of 8 hrs.)

1 FHWA, Final Environmental Impact Statement Pursuant to Section 102 (2) (C), P.L. 91-190. Noise Standards and Procedures (FHWA EIS-72-020F, Washington, D.C., November, 1972)16-17.

2 US Department of Housing And Urban Development, Department Circular 1390.2. Noise Abatement and Control: Departmental Policy, Implementation Responsibilities, and Standards (Washington, D.C., August 4,1972).

Prediction of Noise Levels

Determination of the noise level near an existing highway simply involves taking a series of readings over a sufficient time interval at appropriate locations near the highway.

Direct measurement is not possible, however, when noise levels near an uncompleted highway project are desired, when traffic patterns have not yet reached the ultimate levels, or when some nearby action such as construction of a barrier or removal of a forest, may affect the noise pattern. Furthermore, direct measurement may not be practical in large scale projects where data on thousands of points along many miles of highway is desired. In these cases, use of one of many noise prediction techniques is appropriate. The following are two techniques which are readily available for use:

Traffic Noise Prediction Model MOD 2
A computer program described in Report
No. DOT-TSC-FHWA-72-1 available from
National Technical Information Service
Springfield, Virginia 22151

Highway Noise - A Design Guide for Highway Engineers
National Cooperative Highway Research
Program Report 117 available from
Highway Research Board
National Academy of Sciences

Updated: 07/14/2011
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