The Audible Landscape
2 Summary of Noise Reduction Techniques
This manual describes a variety of techniques for achieving noise-compatible land uses near highways. The techniques are of two types: administrative techniques which can be used by local government officials to require or encourage improved noise compatibility, and the physical methods available to architects, developers and builders for achieving the desired noise impact reduction. This section provides a very brief summary of the administrative techniques and physical methods which are described in detail in sections 3 and 4, respectively.
2.1 Administrative Techniques
The administrative techniques available to local governments to encourage noise-compatible land use control near highways fall into five categories:
- other legal restrictions, such as subdivision laws, building and health codes
- municipal ownership or control of the land
- financial incentives for compatible use
- educational and advisory municipal services
Zoning can be a strong local control on the type of new development, but has little control over existing land uses. The principal uses of zoning as a noise compatibility control are:
- Exclusion of typically incompatible uses, such as residences, from a noise-impacted area by allowing only industrial or agricultural uses. This is a simple and effective technique. However, such zoning may conflict with other plans for community growth, and it may render the land worthless if no demand exists for industrial or agricultural land.
- Regulation of specific details of development design or construction, such as limits on building height or requirements for buffer strips, noise barriers, and sound insulating construction. This is usually effective, but often the applicability of the requirements extends to buildings that do not need the special construction techniques to be noise compatible.
- Zoning can permit special development concepts such as cluster and planned unit development. These forms of incentive zoning make possible developments with significant advantages over the conventional subdivision.
Other Legal Restrictions
Municipal ordinances other than zoning can act as noise compatible land use controls:
- Subdivision or development standards can regulate details of larger developments to require acoustical site planning of the development or to require berms and barriers. These standards often do not apply to new construction on individual lots in a previously developed area.
- Building codes can specify construction details such as acoustic insulation and sealed windows, or, they can require that certain noise levels not be exceeded within a building. However, they cannot specify such things as acoustical site planning, which may in many instances be a more desirable alternative than insulation and sealed windows.
- Health codes can specify noise levels which are not to be exceeded if a building is to be habitable. Health codes have the potential of being one of the most consistently effective noise compatibility controls.
- Local laws can require that an occupancy permit be received before a building can be used. Issuance of the permit can be withheld unless all provisions of zoning, subdivision, building, and health codes have been met. This can be an exceptionally effective enforcement mechanism.
- A special permit procedure requiring individual review of each building application can exist either as part of a zoning ordinance or as a general municipal ordinance. Thus an administrative body in the municipal government can grant or deny the permit based on a judgment of the merits of each specific case. This has the advantage of individual case-specific judgment and the possible disadvantage of being subject to arbitrary decisions of a poorly staffed permit review board.
- Environmental impact statements can be required in some states for new development projects. These can contain a noise impact section which would require site specific acoustical analysis. This information can act as a valuable aid for municipal officials who must make decisions on the appropriateness of any permit applications.
Municipal Ownership or Other Control of the Land
If the municipality owns the noise-impacted land, it can keep the land vacant or see that it is developed only with noise compatible uses. Acquisition can be accomplished by several techniques:
- The land can be purchased, but often at significant cost.
- The land can be taken by eminent domain under certain situations, but this can be extremely costly and locally unpopular.
- Land can be received as a gift, as a condition of subdivision approval, as a transfer from other government agencies, or in trade for other municipally owned land.
- The municipality can obtain, through purchase or otherwise, an easement which restricts the land without an actual transfer of ownership. This may often represent a low cost way to obtain strict land use control.
While a financial incentive may not have the absolute strength of enforcement that municipal ownership and legal regulations have, it can be effective. Financial incentive can take two forms:
- Undeveloped and underdeveloped land can be assessed at a low rate. This will reduce pressure on landowners to sell or develop land which they can no longer afford to keep because of high property taxes. Although this reduces the tax base, it also saves the significant costs of new municipal services which would be required if the land were developed.
- Relaxation of enforcement of provisions of municipal regulations can, where legal, be used as an incentive to obtain voluntary acoustical site design and construction measures from developers and builders.
Educational and Advisory Municipal Services
Often, builders and developers are unaware of noise compatibility measures which can be incorporated into a development at little cost. The municipal government can, at very low cost, provide information to the builders, developers, architectural firms, and the public in general, to generate the necessary awareness. These municipal information services can take four forms:
- An architectural review board can be created, consisting of part-time citizen volunteers who are skilled in architecture, acoustics, and related fields. This board can evaluate all new development plans. Its effectiveness is a function of the support given it by other municipal officials.
- A municipal design service can exist either formally or informally as part of the various permit application review procedures.
- An acoustical information library can be maintained by the municipality as a reference source for local builders and developers.
- A public information effort can result in a public awareness of noise incompatibilities and their prevention. This, in turn,could affect the marketability of incompatible homes and other development, placing financial pressure on builders and developers to achieve noise compatibility.
2.2 Physical Methods to Reduce Noise Impact
Physical noise reduction techniques can be grouped into four major categories:
- acoustical site planning
- acoustical architectural design
- acoustical construction
- noise barriers
These physical techniques vary widely in their noise reduction characteristics, their costs, and especially, in their applicability to specific locations and conditions.
Acoustical Site Planning Acoustical site planning uses the arrangement of buildings on a tract of land to minimize noise impacts by capitalizing on the site's natural shape and contours. Opportunities for successful acoustical site planning are determined by the size of the lot, the terrain, and the zoning. In general, conventional zoning patterns lack the flexibility necessary to permit innovative site planning techniques. A possible way to achieve the needed flexibility is through the use of cluster and planned unit development techniques. Acoustical site planning techniques include:
- Placing as much distance as possible between the noise source and the noise sensitive activity;
- Placing noise-compatible activities such as parking lots, open space, and commercial facilities, between the noise source and the sensitive activity;
- Using buildings as barriers;
- Orienting noise-sensitive buildings to face away from the noise source.
Acoustical Architectural Design Acoustical architectural design incorporates noise-reducing concepts in the details of individual buildings. The areas of architectural concern include building height, room arrangement, window placement, and balcony and courtyard design. For example, in some cases, noise impacts can be reduced if the building is limited to one story; and if bedrooms and living rooms are placed in the part of the building which is farthest from the noise source while kitchens and bathrooms are placed closer to the noise source.
Acoustical Construction Acoustical building construction is the treatment of the various parts of a building to reduce interior noise impacts. It includes the use of walls, windows, doors, ceilings and floors that have been treated to reduce sound transmission into a building. The use of dense materials and the use of airspaces within materials are the principle noise reduction techniques behind acoustical construction. Acoustical construction can be an expensive technique, especially when added to an existing building; however, it need not be prohibitively expensive in new construction. It is one of the most effective ways of reducing interior noise.
Noise Barriers Noise barriers can be erected between noise sources and noise-sensitive areas. Barrier types include berms made of sloping mounds of earth, walls and fences constructed of a variety of materials, thick plantings of trees and shrubs, and combinations of these materials. The choice between these depends on a variety of factors, including the desired level of sound reduction, space, cost, safety and aesthetics.
2.3 Implementation Strategies
An implementation strategy, using normal administrative structure, is presented for a noise compatibility land use control program. The strategy is divided into five major phases: 1) problem identification, 2) examination and selection of administrative techniques suited to the locality, 3) study of legal status, 4) study of State legislative changes, and 5) implementation. Since considerable time might be required to implement this strategy, a stopgap procedure is also presented.
The problems posed by the implementation of this manual are enumerated These problems include: 1) public apathy, 2) limitations under State laws, 3) financial cost to the municipal government, 4) negative physical and aesthetic side effects, 5) opposition with private interests, and 6) conflicts with local tradition.
Other sources of information regarding issues on highway noise control are listed. These sources provide comprehensive information in the area of acoustics, the effects of noise, noise standards, prediction techniques, impact reduction techniques, and noise control legislation.