1、AASHTO TITLE GTN-3 93 = 0637804 0024174 717 m Guide on Evaluation and Abatement of Traffic Noise 1993 Prepared by the AASHTO Highway Subcommittee on Design Task Force for Environmental Design Published by the American Association of State High way and Transportation Officials AASHTO TITLE GTN-3 93 m
2、 Ob39804 0024175 653 W Guide on Evaluation and Abatement of Traffic Noise 1993 Prepared by the AASHTO Highway Subcommittee on Design Task Force for Environmental Design Published by the American Association of State Hgh way and Transportation Officials O Copyright, 1993 by the American Association o
3、f State Highway and Transportation Officials. All rights reserved. This book or any parts thereof may not be reproduced in any form without the written permission of the publisher. AASHTO TITLE GTN-3 93 Ob39804 0024376 5T ISBN 1-56051 -062-5 1993 AASHTO EXECUTIVE COMMITTEE President: Wayne Muri, Mis
4、souri Vice President: Howard Yenisdim Secretary-Treasurer: Clyde Pyers, Maryland Elected Regional Members Region I Region I Charles OLeary, New Hampshire Wayne Shackelford, Georgia Region III Region IV Kirk Brown, Illinois Non-Voting Members Immediate Past President: A. Ray Chamberlain AASHTO Execut
5、ive Director: Francis B. Francois 1993 AASHTO TASK FORCE FOR ENVIRONMENTAL DESIGN Chaiman: Robert P. Mickelson, Arizona Vice Chaiman: Raymond D. Richter, Delaware Secretary: C. Larry King Region I Raymond D. Richter, Delaware Bruce Brumfield, New Jersey David H. Fasser, New York Fred W. Bowser, Penn
6、sylvania C. Larry King, FHWA Region II Charles Raymer, Kentucky Charles M. Higgins, Louisiana William M. DuBose III, South Carolina Randolph Epperly, West Virginia Region iII Lawrence E. Foote, Minnesota William R. Yarnell, Missouri Region IV Robert P. Mickelson, Arizona Ed Kress, California Charlie
7、 Rountree, Idaho Eb Engelmann, Oregon Harry Underwood, Wyoming AASHTO TITLE GTN-3 93 W Ob39804 0024178 362 1993 AASHTO HIGHWAY SUBCOMMITTEE ON DESIGN Chairman: Dan Flowers, Arkansas Vice Chairman: Kenneth C. Afferton, New Jersey Secretary: Thomas Willett. FHWA Alabama, Don Arkle, Ray D. Bass, J. F.
8、Caraway Alaska, Ray Shuniway Arizona, Robert P. Mickelson, Dallis B. Saxton, John L. Louis Arkansas, Bob Walters, Paul DeBusk California, Waiter P. Smith Colorado, James E. Siebels Connecticut, Earle R. Munroe, Bradley J. Smith, James F. Byrnes, Jr. Delaware, Michael A. Angelo, Chao H. Hu D.C., Char
9、les F. Williams, Sanford H. Vinick Florida, Bill Deyo, Freddie Simmons Georgia, Walker Scott, Hoyt J. Lively, Roland Hinners Hawaii, Kenneth W. G. Wong, Roland Hinners Idaho, Richard Sorensen, Jeff R. Miles Illinois, Ken Lazar, Dennis Pescitelli Indiana, David M. Pluckebaum Iowa, George F. Sisson, D
10、onald L. East, Dave Little Kansas, Warren Sick, James Brewer, Richard G. Adams Kentucky, Charles S. Raymer, John Sacksteder, Steve Williams Louisiana, Al Dunns, William Hickey, Nick Kalivado Maine, Charles A. Valley, Walter Henrickson Maryland, Steve Drumm, Robert D. Douglass Massachusetts, Sherman
11、Eidelman, Stanley W. Woods, Jr. Michigan, Charles J. Arnold Minnesota, Roger M. Hili Mississippi, Wendel T. Ruff, J. Richard Young Missouri, Frank Carroll, Bob Sfreddo Montana, David S. Johnson, Ronald E. Williams, Carl S. Peil Nebraska, Donald L. Turek, Eldon D. Poppe Nevada, Michael W. McFall, Ste
12、ve R. Oxoby New Hampshire, Gilbert S. Rogers New Jersey, Kenneth Afferton, Walter W. Caddell, Charles A. Goessel, Jim Snyder New Mexico, Joseph Pacheco, Charles V. P. Trujillo New York, J. Robert Lambert, Philip J. Clark, Robert A. Dennison North Carolina, D. R. (Don) Morton, G. T. (Tom) Shearin, J.
13、 T. Peacock, Jr. North Dakota, David K. O. Leer, Ken Birst Ohio, Donald K. Huhman, Christopher L. Runyan AASHTO TITLE GTN-3 93 W Ob39804 0024379 2T9 W Oklahoma, Bruce E. Taylor, C. Wayne Philliber Oregon, Tom Lulay Pennsylvania, Fred W. Bowser, John J. Faiella, Jr., Dean Schreiber Puerto Rico, Jose
14、E. Hernandez, Maria M. Casse, Eugenio Davila Rhode Island, J. Michael Bennett South Carolina, Robert Pratt, William M. DuBose South Dakota, Larry Engbrecht, Monte Schneider, Timothy Bjorneberg Tennessee, Paul Momson, Clellon Loveall Texas, Frank D. Holzmann, William A. Lancaster, Mark Marek U.S. DOT
15、, John Rice (FAA), Thomas O. Willett (FHWA) Utah, Dyke LeFevre, P. K. Mohanty, Heber Vlam Vermont, Robert M. Murphy, Donald H. Lathrop, John L. Armstrong Virginia, E. C. Cochran, Jr., R. E. Atherton, K. F. Phillips Washington, Dennis Jackson West Virginia, Norman Roush, Randolph Epperly Wisconsin, J
16、oseph W. Dresser, Robert Pfeiffer Wyoming, Donald A. Carlson AFFILIATE MEMBERS Alberta, Allan Kwan Hong Kong, S. K. Kwei Manitoba, A. Boychuk Mariana Islands, Elizabeth H. Salas-Balajadia New Brunswick, C. Herbert Page Newfoundland, Terry McCarthy Northwest Temtories, Peter Vician Nova Scotia, Donal
17、d W. MacIntosh Ontario, Gerry McMillan Saskatchewan, Tom Gutek ASSOCIATE Mass. Metro. Dist. Comm., E. Leo Lydon N. J. Turnpike Authority, Arthur A. Linfante, Jr. Port Authority of NY as the balloon expands and its radius becomes greater, its surface area increases. Similarly, as the sound wave front
18、 moves away from its source and the surface area of the front increases, the acoustic energy in the wave decreases in proportion to the square of the distance from the source. Sound from a line source is made up of the sounds from each of the point sources, Energy losses occur due to friction. But s
19、imply stated, the intensity of the sound wave decreases as the distance from the source in- creases. If an obstacle or barrier, such as a wall, is placed in the path of a wave front, a portion of the sound will be reflected by the obstacle, another por- tion may be absorbed by it, and yet another po
20、rtion may be transmitted through it. In addition, a portion of the wave front that clears the top and ends of the obstacle will be bent or diffracted resulting in a “shadow“ zone (Figure 1). The abating effect of a barrier is therefore dependent upon its dimensions and on the properties of the const
21、ruction materials. Adense, compact material with considerable mass will allow virtually no sound to pass through. This is a desirable quality for abating structures. A dense, smooth surface will reflect more sound than a porous, compressive substance. A porous, compressible material will absorb rath
22、er than reflect a portion of the sound striking it. However, it will allow a substantial portion of the sound to pass through the barrier unless it is backed by a dense, tight material. 2 AASHTO TITLE GTN-3 73 Ob37804 002i1185 5T2 Guide on Evaluation and Abatement of Trafik Noise The amount of noise
23、 finding its way into the shadow zone by diffrac- tion is dependent on the frequency of the noise source, curvature of the wave front, and angle of incidence. The effect on an observer is dependent on the observers distance beyond the barrier and on the barrier height and length. SH 2 x 10- Using dB
24、 instead of pressure units, the sound pressure levels of all likely sounds are covered on a scale of O to about 140 (Figure 2). The ref- erence for sound pressure measurements is O dB, which corresponds to 0.0002 microbars. This represents the weakest sound that can be heard in an extremely quiet pl
25、ace by a person with very good hearing. A sound level of 100 dB corresponds to pressure of 20 microbars, or 100,000 times the pressure O dB. The range of sound pressure levels most frequently encoun- tered in evaluating traffic-generated noise on highways is 50 to 95 dB. 2.3 Frequency and Loudness S
26、ound pressure level alone cannot be taken as an indication of loud- ness. The frequency of a sound wave is the number of times it repeats itself in each second (i.e., the rapidity with which the pressure fluctuations oc- cur). Frequency is expressed in hertz (Hz). One hertz is one cycle per sec- ond
27、. The audible range of frequency is from 20 to 20,000 Hz, but the ear is much more sensitive to sounds with frequencies near 1,000 Hz than to those near the range extremes. In order for a sound at 100 Hz to seem as loud as a sound at 1,000 Hz, the pressure level would have to be about 20 dB greater
28、at the lower frequency. Most traffic noise has frequencies in the 100 to 4,000 Hz range, with engine noises occurring within the lower frequencies (100-250 Hz) and tire whine and wind turbulence occurring toward the upper limit of the range. Very few sounds are pure tones (i.e., consisting of a sing
29、le frequency). To measure sound precisely, it would be necessary to measure pressure levels for each of the multitude of frequencies which make up the sound. It usually is not convenient to measure a sound level in this manner. A simpli- fied procedure consists of dividing the audible range of frequ
30、encies into 9 octave bands, obtaining pressure levels for each band, and then combining the results into a single value. By weighting the sound pressure level for 5 AASHTO TITLE GTN-3 93 m Ob39804 0024388 201 m Guide on Evaluation and Abatement of Traffic Noise each octave band, an aggregate value c
31、an be obtained which approximates the response of the human ear to the sound pressure of the composite fre- quency. The A-weighted network most closely represents the range of hu- man hearing and its response to traffic noise. The resulting sound level is represented by dBA. 2.4 Fluctuations in Traf
32、fic Noise In assessing noise levels, the peak variation over a period of time is an important consideration. Occasional loud noises may be accepted with little complaint, but repeated high levels are usually a major problem in noise-sensitive areas. Moreover, it is far more costly to provide protect
33、ion against the occasional loud noise than to protect against frequently recur- ring low-level noises. For providing noise protective measures where they will do the most good for the lowest expenditure, one should consider the maximum duration of exposure of the greater sound levels. One factor whi
34、ch annoys and disturbs human activity is the magni- tude of the loudest noise events which occur. Another factor is the repeti- tiveness of these loud noise events. For example, a few repetitions of a loud noise each day will not be particularly bothersome and will not warrant much attention. Severa
35、l repetitions per hour could be quite objectionable. A third factor is the sustained or continuous nature of the noise. An equivalent sound level descriptor (Leq), which is based on the av- erage acoustic intensity over time, has gained wide acceptance as a good representation of these three factors
36、. The equivalent sound level, Leq, rep- resents the sound level which, if held constant over a specified period of time, would contain the same total acoustic energy as the actual fluctuating sound level during the same time period. It is defined as: N Leq = 10 log10 T 1 c loLylo 1 t= 1 where Lt is
37、the sound level measured in dBA, T is total time, and t is the increment of time. Because Leq represents the average acoustic energy of the time pat- tern, it is a more versatile descriptor than the percentile descriptors, such as 6 Guide on Evaluation and Abatement of Traffic Noise LIO. The indicat
38、or Li0 represents the noise level which is exceeded 10 per- cent of the time period under consideration. The equivalent A-weighted sound level (Leq dBA) is intended as a single number indicator to describe the mean energy or intensity level over a specified period of time during which the sound leve
39、l fluctuated. The value of Leq can be evaluated continuously with the proper instrumentation or it can be derived from individual, closely-spaced samples over smaller intervals in time. Under traffic conditions of low volume or interrupted traffic flow, the Kq can represent an excellent means of des
40、cribing the noise environment. Because the Le, is not influenced by the variability of the noise time pat- tem, it is an effective way to compare or combine noises with differing time histories. The time period over which the Le, is developed may be taken as 1-hour, 24-hour, or even a 15-hour daytim
41、e and 9-hour nighttime period. Currently, a 1-hour time period is used for Leq. 2.5 Principles of Sound Generation and Human Responses A few general relationships may be helpful in understanding some of the principles of sound generation and human response. A doubling of the traffic volume at the so
42、urce produces a 3 dBA increase in the sound level. Subjective tests have determined that the smallest change in noise level perceptible to the ear is approximately 3 dBA and that an increase of 10 dBA will cause the noise to sound about twice as loud to the average listener (Table 1). If a traffic s
43、tream of 400 vehicles per hour (vph), for example, produces a noise level of 50 dBA at a certain distance from the observer, 800 vph traveling at the same speed and under identical conditions would produce 53 dBA, a change which is hardly noticeable. A further increase to 1,600 vph would produce 56
44、dBA and 4,000 vph, about 60 dBA. Thus, a tenfold increase in traffic volume would result in an increase of 10 dBA and would sound about twice as loud to the average listener as 400 vph. A decrease of 10 dBA will appear to an observer to be a halving of the apparent loudness. For example, a noise of
45、70 dBA will sound only half as 7 loud as 80 dBA, assuming the same frequency composition and other things being equal. Sound Levei Change Table 1 : Relations Between Decibels, Energy, And Loudness Relative Loudness Acoustic Energy Loss -3 dBA -10 dBA -20 dBA II OdBA 11 O II Reference 50% Perceptible
46、 Change 90% Half as Loud 99% 1/4 as Loud -30 dBA -40 dBA - 99.9% 1/8 as Loud 99.99% 1/16 as Loud As mentioned earlier, sound intensity decreases with distance from a source. Noise from a line source, such as a continuous stream of vehicles, varies differently with distance because sound pressure wav
47、es originate ail along the line and converge at the point of measurement. The wave front approximates an expanding cylinder. As a result, the noise level will de- crease from 3 to 4.5 dBA for each doubling of distance from the source. The amount of decrease depends on the absorptive characteristics
48、of the ground. 2.6 Summary Sound is a disturbance produced by the vibration of some material body. It is transmitted through air or any other medium in the form of lon- gitudinal waves. The impact that sound waves have on the hearing organs is dependent on the pressure generated by the wave. The uni
49、t of measure of sound pressure level in common use is the decibel (dB). The decibel scale is a logarithmic function of the relative sound pressure. The hearing mecha- nism is sensitive to the frequency of the sound waves as well as to sound pressure level. The A-weighted network most closely represents the range of human hearing and its response to traffic noise. 8 AASHTO TITLE GTN-3 93 Ob39804 0024373 8Tb m Guide on Evaluation and Abatement of Traffic Noise - Sound diminishes in intensity as the square of the distance from the source. The sound level will decrease approxi
