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Polcak is SeniorTransportation Engineer,Maryland State HighwayAdministration,Baltimore. Miller isSenior Vice President,Harris Miller Miller &Hanson, Inc., Burlington,Massachusetts.

The goal of environmental sustainability pre-sents new challenges to traditional notions ofhow transportation systems and their com-

ponents affect the quality of life. For transportationnoise control, the shift to planning for sustainabilityadvances the concept of the soundscape or soundenvironment. In this context, the quality of life isimproved to the extent that the soundscape isdeemed desirable—that is, appropriate for the loca-tion and the associated activity.

Traditional noise control strategies focus on onesound source at a time and target the intensity orloudness of that source. In contrast, the evaluation ofa soundscape considers a multitude of sources andthe desirability of their combinations.

Transportation design requires standards orguidelines, but few metrics are associated withsoundscape desirability. To pursue desirable sound-scapes as part of the transportation planning process,policy makers, engineers, and design professionalswill need to understand subjective judgments aboutthe sonic environment. Soundscape considerationsare likely to alter the analysis and design processes,particularly in relation to noise barriers, quieter pave-ment, and source reduction.

Role of SoundscapesThe “triple bottom line” for sustainability requires atransportation project that is economical, environ-mentally friendly, and improves the quality of life. Alltransportation modes create some level of noise forthose living in the vicinity. Improvements to thesoundscape must address not only the undesirableaspects of noise produced by transportation but alsothe preservation or restoration of the desirablesounds that are covered up or masked by trans-portation noise. For transportation improvements orexpansions to achieve the triple bottom line, the fullpanoply of sounds must be considered, with the goalof preserving or restoring desirable soundscapes.

The soundscape is the total sound environment“with emphasis on the way it is perceived and under-stood by the individual or by a society” (1). In otherwords, a proper analysis must understand a sound-scape’s subjective meaning for the individuals whoexperience it.

Judgments of a soundscape may depend on itslocation and visual appearance (2), the type of activ-ity or activities that occur (3), and the observer’s per-sonal history, expectations, emotional reaction,culture (4), and age (5). Evaluating this multiplicityof factors so that decisions can be made about sound-scape improvement or preservation is a formidablechallenge.

Noise ControlA three-pronged approach has guided environmen-tal noise control and management and the noisereduction strategies for highway traffic (6):

u Quieting the source, u Reducing noise along the path of transmission

between the source and the receiver, andu Land use planning.

The first two are direct abatement strategies thatfor a long time have been the foundation for effec-

SoundscapesA Sustainability Approach to Transportation Noise ManagementK E N N E T H D . P O L C A K A N D N I C H O L A S P. M I L L E R

Environmental Sustainability in Transportation

Noise walls are atraditional option fornoise control, butincorporating sustain -ability into planningrequires evaluating anarea’s soundscape.

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tively reducing the impacts of noise in communitiesnear transportation facilities. Whether the facility isa commuter rail line, an airport, or a major highway,the overarching efforts since the landmark environ-mental regulations of the early 1970s have focusedon these two components in the approach to noisecontrol. Which of the two yields the most benefitswill depend on the particular mode of transportationinvolved and on the particular situation.

Land use planning, the third prong in theapproach to transportation noise control, may beviewed as a strategy of avoidance, as opposed toabatement. For example, prohibiting new residentialdevelopment along a major Interstate highway willavoid a noise impact scenario; the goal is to promoteor allow only development or activity that is com-patible with the level of noise in an area. Noise abate-ment, in contrast, would require a noise barrier forthe new residential development along the Interstate.

In applying the concept of soundscape to the abate-ment of highway traffic noise, the focus is less on thephysical reduction in the level of noise and more onhow the traffic noise is perceived as a component ofthe sonic environment. With the trend to sustainabledevelopment and sustainability, new developmentstend to be more compact, urban-oriented environs,and the spaces that are created will have soundscapesthat differ from those in the more traditional livingspaces that characterize many suburban or rural envi-ronments. In either case, the totality of the sonic envi-ronment and the context of the various soundsindigenous to the area may be viewed in terms of theircontribution to the quality of the environment.

Quieting the SourceAutomobile and truck industry efforts have madesteady progress in quieting the source. The primarysubsources of noise from highway vehicles—theengine, the exhaust, and the drive train—haveundergone technological advances and designimprovements in the past 20 to 30 years that haveresulted in some noise reductions. With theseadvances and increasingly stringent vehicle noisestandards, a clear trend to quieter vehicles—partic-ularly in heavy trucks—is emerging in the fleet.

In addition, the development of alternative-fuelvehicles—for example, hybrid and electric—hasachieved a new level of quieting at the source. Designmodifications to truck engine enclosures, improvedmuffler systems, and other redesigned vehicle com-ponents also have yielded noise reductions.

Tire–pavement interaction is another major sub-source of noise from highway vehicles—it is the pri-mary source of traffic noise for most roads and formost vehicles at speeds above 30 mph (7). Althoughthe physical quieting of many vehicle componentshas been accomplished gradually and through attri-tion—with older, noisier vehicles being replaced—quieter pavement technology has developed onlyrecently.

A quieter pavement surface can result in imme-diate reductions or alterations of source noise. Qui-eter pavements perhaps are not an alternative totraditional noise barriers but offer an additionaloption in the noise control arsenal, despite issueswith the longevity and durability of their quietingaspects.

As it crosses over thecampus of the IllinoisInstitute of Technology inChicago, a train on theGreen Line travelsthrough a noise barrier.

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Influencing PerceptionThese efforts at quieting or altering the character ofparticular sources or subsources of noise are impor-tant to the soundscape approach. Traditional noiseabatement seeks to reduce offending or unwantedsounds according to established numerical criteria orlimits; in contrast, the soundscape approach focuseson the human perception of the acoustic environ-ment and on “sounds of preference” (8) that con-tribute to human enjoyment or well-being—that is,to quality of life.

Because the soundscape concept focuses on theidentification, perception, and characterization ofsounds in the total aural environment, the ability toalter the character of the contributing sounds pre-sents an opportunity to influence the perception ofthe sound or noise in a positive way. In an environ-ment in which multiple sources may contribute tothe overall sound energy, the perception of domi-nant sounds, which are judged as negative or unde-sirable, and of sounds that are masked oroverwhelmed complicates assessments of an indi-vidual’s annoyance or satisfaction.

For example, human-made sounds—such as traf-fic noise—that mask the natural or desirable soundsindigenous to an area or community would typicallybe viewed as degrading the environment. Sounds areprocessed differently according to an individual’s cul-ture or experience, so that the same acoustical eventcan yield different meanings and interpretations,depending on the situation (9).

Path ControlNoise reduction at the source or subsource level canbe effective, depending on the transportation mode.Reductions in the overall noise effects of aircraft, forexample, have resulted principally from designimprovements to the engine and airframe to quietnoise, as well as from operational modifications dur-

ing take-offs and landings. In contrast, highway traf-fic noise abatement has relied on noise barriers as theprimary and most effective approach.

As noted earlier, the concept of sustainability andsustainable development fosters a design philosophyand characteristics, conditions, and practices differ-ent from more traditional development scenarios.Suburban sprawl—that is, suburban developmentthat is centered on the single-lot, single-familydwelling—comes with a closer-to-nature atmosphereof open space, wooded areas, and backyards.

Noise barriers target the single primary noisesource—for example, an adjacent highway—andprovide a means of restoring or improving the sound-scape by reducing the intrusive and typically domi-nant traffic noise and by simultaneously unmaskingother desirable natural sounds in the community,such as birdsong or rustling leaves. Although noteliminated, the traffic noise can be relegated to abackground component.

In a sustainable development scenario, however,a more urbanized, compact approach to housing,along with a more pedestrian and public transit ori-entation, fosters greater use of public spaces, pro-ducing a more complex soundscape. Multiple soundsources affect audibility and may vary in time andduration, making the assessment of the soundscapes’contribution to the quality of life challenging andcomplex. An assessment must include not only theA-weighted sound pressure level but also the linkwith psychoacoustic parameters to accommodate themultidimensional nature of perception (10).

Acceptable NoiseFor soundscapes, the context or prevailing environ-ment can have a substantial effect on how a particu-lar sound is perceived. For example, a study of amajor urban district in Kyoto, Japan, found that traf-fic noise was generally considered a positive sign ofcommercial activity, and rarely was characterized asan annoyance (11). Would traditional noise abate-ment strategies yield substantial benefits? In a sub-urban or rural context, that same traffic noise morelikely would be viewed negatively, and abatementmeasures would be highly valued.

As the example suggests, inhabitants of moreurbanized places may perceive transportation noiseas less of an annoyance and perhaps more acceptablewithin the soundscape. As a result, the desire fortransportation noise abatement in urban settings maybe expected to be reduced or at least altered, depend-ing on the characteristics of the area.

In addition, the physical parameters of the devel-opment—for example, the presence of multistory,high-rise residences—may preclude the effective use

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A soundscape approachmasks transportationnoise while allowingdesirable sounds, likethose of the naturalenvironment, to beheard.

Design modificationssuch as turbine chevronscan decrease aircraftnoise.

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of such traditional abatement measures as noise bar-riers, although absorptive or quieter pavements maybe effective in reducing the prominence or at least inaltering the character of the traffic noise.

Assessing Community ImpactIn the suburban setting, the traditional approach totraffic noise abatement is focused on substantiallyreducing the noise level from the highway source. Inthe majority of circumstances, this approach willyield meaningful and beneficial results for the com-munity. But when the soundscape is more complexand varied, with both positive and negative contrib-utory sources, additional attention may be needed topreserve or enhance the soundscape according tothe community’s preferences. An assessment of thetotal soundscape, beyond the numerical noise levels,would be informative.

This more integrated approach would requiremore effort in assessing community impacts. Studieson soundscapes often involve surveys and question-naires that probe the attitudes, expectations, andpreferences of the community residents. The studieshave found that the context of the various sounds,including both visual and sonic cues, has a majoreffect on the judgment of sound quality. Soundscapestudies also can involve laboratory-based experi-ments with recorded data and statistical analysis offeedback from study participants.

Researching SoundscapesResearch comparing field measurements of quieterpavements has revealed that shifts away from thehigher frequencies, to which the human ear is moresensitive, could translate into a more positive ratingor perception of traffic noise as a component of thesoundscape. Similarly, changes in the frequency char-acteristics of the traffic noise that reflects or echoesoff of a building facade or other structure also couldaffect the perception. These shifts in frequency oftenare perceived as a change in the character of the noisesource.

In 2004, a laboratory-based soundscape experi-ment explored perceptions of the effects of a roadsidetraffic noise barrier (12). Participants listened torecordings of conditions before and after a roadsidenoise barrier was built and were asked to determineif the randomly selected sounds were with or with-out the noise barrier. In addition, participants wereasked to describe the cues they used to discriminatebetween the with-barrier and without-barrier sam-ples.

The results indicated that the noise barrier causedperceivable changes in the soundscape and that thechanges could be interpreted as positive (13). The

primary finding was that the noise barrier made thetraffic noise in the soundscape more homogeneous,or less variable, which in general is perceived as moredesirable. The noise barrier reduced higher fre-quency sound but made difficult the identification ofsingle vehicle pass-bys and of changes in direction-ality—that is, the perceived relative position of sin-gle vehicles and their direction of movement.

Land Use and SoundscapesThe consideration of prevailing environmental noiseconditions in land use planning—the third prong innoise reduction strategy—seeks to design or directdevelopment compatible with the prevailing noiseenvironment. The strategy is an exercise in avoid-ance—that is, avoiding the introduction of noise-sensitive activities into an already noisy environ -ment. The approach also tends to focus on the neg-ative aspects of the sonic environment and does notseek to change it but to adapt to it.

In applying the concept of the soundscape, thegoal is to improve the relationship between the auralspace and the people in the living environment (13).The soundscape approach includes management ofthe elements of the acoustic environment that are ofhigh quality and value to people, either throughacoustic design or by management of the outdoorspace, much in the same way that landscape designis applied to improve visual perception of the envi-ronment (8).

Crafting SoundscapesIn summary, sustainable development practicesrequire the consideration and assessment of how the

In Kyoto, Japan, andother areas, traffic noiseis perceived as a sign of ahealthy economy andrarely is considered anannoyance.

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physical effects of traditional traffic noise controlmeasures affect the soundscape as a whole. The con-sideration of soundscape as a gauge of environmen-tal quality, however, has an inherent complication—multiple variables, contextual and subjective, influ-ence individuals’ perceptions of the sonic environ-ment (9). The context therefore includes culturaland personal preferences, sensitivities, and attitudes.

An improvement in the soundscape does notinvolve noise level reduction only (9). The challengeis to craft meaningful and effective links between thetangible—sound levels and decibel values—and theintangible, multidimensional nature of human per-ception.

References 1. Truax, B. (ed.) Handbook for Acoustic Ecology. ARC Pub-

S oundscapes are complex. A soundscape is the all-encom-passing, audible environment experienced in a specific

location. In considering a soundscape’s effect on quality of life,the question to answer is “How can the soundscape be judgedin a way that will facilitate improvement?”

Improving SoundscapesFor decades, efforts to improve soundscapes have focused onnoise control, treating a single source at a time, seeking improve-ment by minimizing annoyance, limiting noise as quantified bya single noise metric, such as the day–night sound level or thecommunity noise equivalent level. This approach has been suc-cessful, so that fewer numbers of residents are exposed to highernoise levels and presumably experience less annoyance.

But consideration of the entire soundscape needs to addressmultiple sources, some undesirable, some desirable. The noisecontrol approach focuses on one undesirable source at a time anddoes not consider desirable sounds or judge which undesirablesound most needs quieting. Improving soundscapes means reduc-ing the noise from undesirable sources and permitting the desir-able ones to be heard.

Judging SoundscapesJust as the concept of annoyance has been used to summarizethe multiple adverse effects of transportation noise on people,a simplifying subjective judgment may emerge to summarizethe human factors, experiences, and emotions that influencea person’s reaction to a soundscape. For instance, a sound-

scape’s contribution to quality of life could be summarized byrating the components of the soundscape on a scale of desir-ability.

One method of collecting this information is to survey res-idents to identify the sounds they hear and to rate each sound.Desirability could serve as the rating scale, ranging from –4 orextremely undesirable to +4 or extremely desirable. Figure 1(page 37) shows hypothetical results from a survey of resi-dents that readily distinguishes the sounds people like andthose they do not. The values are cumulative, moving fromundesirable at the left to desirable at the right. The morerapidly the cumulative value increases, the less desirable is thesound. Birdsong is desirable for most people, but most rateroad traffic noise as undesirable.

The author is Senior Vice President, Harris Miller Miller &Hanson, Inc., Burlington, Massachusetts.

Judging SoundscapesN I C H O L A S P. M I L L E R

An example of a video for use in laboratory sound tests can befound on You Tube—see footnote on page 37.

A 2004 studyshowed thatnoise wallsreduce higher-frequencysounds andcause trafficnoise to beperceived asmorehomogeneous.

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lications, Vancouver, British Columbia, Canada, 1978.2. Adams, M., T. Cox, G. Moore, B. Crawford, M. Refaee, and

S. Sharples. Sustainable Soundscapes: Noise Policy and theUrban Experience. Urban Studies, Vol. 43, No. 13, Decem-ber 2006, pp. 2385–2398.

3. Yu, L., and J. Kanga. Effects of Social, Demographical andBehavioral Factors on the Sound Level Evaluation inUrban Open Spaces. Journal of the Acoustical Society ofAmerica, Vol. 123, No. 2, February 2008, p. 772.

4. Dubois, D., C. Gustavino, and M. Raimbault. A CognitiveApproach to Urban Soundscapes: Using Verbal Data toAccess Everyday Life Auditory Categories. Acta AcusticaUnited with Acustica, Vol. 92, 2006, pp. 865–874.

5. Yang, W., and J. Kang. Soundscape and Sound Preferencesin Urban Squares: A Case Study in Sheffield. Journal ofUrban Design, Vol. 10. No. 1, February 2005, pp. 61–80.

6. Highway Traffic Noise: Analysis and Abatement Guidance.FHWA-HEP-10-025, Federal Highway Administration,December 2011.

7. Rasmussen, R. O., R. J. Bernhard, U. Sandberg, and E. P.Mun. The Little Book of Quieter Pavements. FHWA-IF-08-

004, Federal Highway Administration, July 2007.8. Brown, A. L. Soundscapes and Environmental Noise Man-

agement. Noise Control Engineering Journal, Vol. 58, No.5, September–October 2010, pp. 493–500.

9. Schulte-Fortkamp, B. The Application of Soundscape inCommunity Noise. Proceedings of Inter-Noise 2007, Istan-bul, Turkey, 2007.

10. Genuit, K., B. Schulte-Fortkamp, and A. Fiebig. Psycho -acoustic Mapping Within the Soundscape Approach. Pro-ceedings of Inter-Noise 2008, Shanghai, China, 2008.

11. Finegold, L. S., and K. Hiamatsu. Linking Soundscapeswith Land Use Planning in Community Noise Manage-ment Policies. Proceedings of Inter-Noise 2003, Seogwipo,Korea, 2003.

12. Nilsson, M. E., T. Kaczamarek, and B. Berglund. PerceivedSoundscape Evaluation of Noise Mitigation Methods. Pro-ceedings of Inter-Noise 2004, Prague, Czech Republic,2004.

13. Lercher, P. Soundscape Research, Quality of Life, andHealth: An Integrated Environmental Health Viewpoint.Proceedings of Inter-Noise 2007, Istanbul, Turkey, 2007.

Guidance for ActionTwo additional questions need to be asked about the ratingsin Figure 1:

u What are the objective sound levels from each source thateach respondent is rating?

u For each source, what is the threshold sound level sepa-rating an undesirable rating from a desirable rating?

The answers can provide noise control design goals foreach source.

The type of data shown in the figure could be acquiredthrough a mail survey, but important questions would remainunanswered:

u Are all respondents hearing the same sounds? u What are the levels of the sounds that respondents hear? u What time of day, week, or year do the ratings represent?

Proper identification of the respondent’s location—and

careful survey wording—could resolve some of these ques-tions, but determining objective sound levels for each sourcefor each person is an expensive and complicated, if not impos-sible, proposition.

Laboratory TrialsAlthough collecting desirability ratings and sound levels insitu would be the gold standard for soundscape analysis, lab-oratory studies could associate human reactions to sound-scapes with metrics of sound. Researchers have had successbringing an outdoor experience into a laboratory setting tojudge outdoor sounds. The technique of using various combi-nations of audio and visual reproductions in the laboratory hasyielded subjective evaluations that correlate closely with eval-uations made in the field.

Laboratory tests could employ high-definition videos andhigh-quality sound to learn how people rate the componentsof different soundscapes, and to test the correlation of vari-ous sound metrics with the ratings.1 The soundscapes wouldbe constructed in the laboratory setting, from separate record-ings of individual sources and of different ambient back-grounds. Patching the soundscapes together would permitaccurate determination of the sound metrics of each con-tributing source—a disaggregation not always possible with insitu measurements.

Laboratory results, especially acquired from subjects whoare not familiar with a specific soundscape, may differ fromthe results that derive from people who live within that sound-scape. But work in the laboratory could help develop a gen-eral understanding of how people subjectively evaluatedifferent soundscapes and the component sound sources andcould test the utility of different noise metrics.

1An example has been uploaded to http://youtu.be/NjOIfUrFcR8. Listen with

high-quality headphones for full effect.

FIGURE 1 Respondent ratings of three sounds in a selectedlocation or neighborhood: extremely undesirable to extremelydesirable.