Making Sound Decisions About Highway Noise Abatement. Pennsylvania Department of Transportation Federal Highway Administration

Transcription

1 Making Sound Decisions About Highway Noise Abatement Pennsylvania Department of Transportation Federal Highway Administration

2 The Noise Abatement Proc e s s PENNDOT assesses the potential noise impacts of highway improvement projects and where appropriate considers noise impact mitigation measures for eligible projects. These State-funded Type II projects are not intended to change or alter current practice concerning Type I or Federally-funded Type II Highway Traffic Noise Abatement projects in the Commonwealth. What are the Types of Noise Projects? Type I Projects are highway projects that would (1) construct a highway on a new location or (2) increase the number of through-traffic lanes or (3) physically alter an existing highway in a way that significantly changes the horizontal or vertical alignments. Type II Projects also called retrofit projects are those that propose noise abatement for existing highways without the improvements listed above. PENNDOT has analyzed and constructed both Federally and State funded Type II projects. Federally funded Type II projects are not mandated by federal regulation and are, therefore, not required or typically supported by Federal aid. If supported, a Federally funded Type II project must adhere to Title 23 Code of Federal Regulations, Part 772 Procedures for Abatement of Highway Traffic Noise and Construction Noise. PENNDOT does not actively participate in funding Type II projects due to resource constra i n t s. H ow e ve r, there have been times when the Pennsylvania General Assembly earmarked State funds, allowing PENNDOT to conduct Type II noise analysis and construct noise barriers. In these cases, the earmarked funds have been limited in amount and also directed to specific geographical areas by certain public officials. As a result of these special allocations, PENNDOT has participated in providing noise abatement on existing highways. These Statefunded Type II projects are the extent of PENNDOT s current programmed study concerning Highway Traffic Noise Abatement along existing roadways. Applying the Process to Eligible Projects There is a specific process that PENNDOT uses to identify communities that will be considered for noise abatement and to determine whether noise abatement measures can be implemented within state and federal guidelines. This process includes the following steps: Identify noise-sensitive areas The first step in the process is to determine which noise-sensitive locations may be affected by a proposed highway project. Noise-sensitive locations, as defined by the Federal Highway Administration, are provided in the following table: Hourly Weighted Sound Levels db(a) For Various Land Use Activity Categories Land Use Activity Exterior Description of Category Leq(h) Land Use Activity Categor y A 57 Lands on 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. B 67 Residences, schools, churches, parks, picnic areas, recreation areas, play grounds, active sports areas, motels, hotels, libraries, and hospitals. C 72 Developed lands, properties, or activities not included in Categories A or B above. D -- Undeveloped lands. E 52 Residences, motels, hotels, public Interior meeting rooms, schools, churches, libraries, hospitals, and auditoriums. Source: Title 23 Code of Federal Regulation, Part

3 Undeveloped Lands Undeveloped lands (Land Use Category D) contain no noise sensitive receptors, and as such are not considered for noise abatement measures. Developed and Developing Lands Highway Traffic Noise analysis will be assessed for developed lands as well as undeveloped lands when they are considered Planned, Designed, and Programmed (i.e. developing lands). Undeveloped lands will be deemed to be Planned, Designed, and Programmed if a noise-sensitive receptor such as a residence, school, church, hospital, library, etc. has received a building permit from the local agency with jurisdiction at the time of the Highway Traffic Noise analysis. In the case of a subdivision, if at least one building permit within the approved development plan has been received from the local agency with jurisdiction at the time of the Highway Traffic Noise analysis, then the entire subdivision will be deemed Planned, Designed, and Programmed. However, PENNDOT is not responsible for considering noise abatement measures for developing lands which receive their building permit after the date of approval of a Categorical Exclusion, issuance of the Finding of No Significant Impact, or Record of Decision is made. Once this date of public knowledge is set, provisions of such noise abatement becomes the responsibility of local communities and private developers. Monitor and model noise levels After noise-sensitive locations that may be affected by the proposed highway project have been identified, existing traffic noise levels are monitored at locations that are representative of affected neighborhoods. The results of these monitoring sessions are used to ensure that the noise prediction model will provide accurate results for each community. Noise abatement decisions and designs are based on the results of running the model for all affected areas. Many people ask why their house was not monitored and assume that they were not considered if monitoring was not done on their property. The monitoring, however, is used only to set up and verify the prediction model and not as a basis for noise abatement decisions. Therefore, even though your property may not be monitored for noise levels, the modeling used for the noise abatement decisions will consider all affected properties. 4 5

4 Consider noise abatement If you attend a public meeting for a highway project that includes a discussion of noise issues, you may hear people talking about warranted, feasible and reasonable. These terms actually describe three steps that PENNDOT must take when considering noise abatement for noise-sensitive areas. To determine whether abatement measures are warranted for residential areas, we first consider the worst case noise levels that can be expected 20 years after the proposed highway project has been constructed, when it is at its maximum capacity. Using criteria based on Federal Highway Administration (FHWA) guidelines, abatement is warranted if the future noise levels approach or exceed the noise abatement criteria, or are elevated by 10 db(a) above the existing conditions. FHWA required each State Department of Transportation to define Approach, which PENNDOT has defined as 1 db(a) below the noise abatement criteria [Exterior Leq(h)] listed in the table on page 3. For communities where noise abatement consideration is warranted, the next step is to consider whether noise abatement would be feasible for each affected community. Traffic noise abatement is typically provided by noise barriers. Feasible noise barriers are those that provide at least 5 db(a) of noise reduction to noise-sensitive locations and pose no safety, engineering, or access restrictions. Your Role in the Process For most highway projects, more than one alternative design is considered. The design of noise barriers begins when a final alignment has been selected for the highway. During the noise barrier design process, you will have opportunities to have your concerns addressed through public meetings. To fully participate, try to attend these meetings, fill out all project questionnaires, and voice your opinions. When it has been determined that a noise barrier would be reasonable, public preferences are considered. If the majority of affected residents do not want a barrier to be built between their properties and the roadway, the barrier will not be built. The community members must inform PENNDOT of this decision before the noise barrier final design process begins. Keep in mind, however, that these decisions are final. If a community decides that it does not want a barrier, it cannot return at a later time to request a barrier. PENNDOT only recommends a noise barrier to be constructed if determined to be warranted, feasible, reasonable and desired by the affected community. If a noise barrier system is determined to be feasible, the next step is to determine whether or not the barrier is reasonable for construction. For a barrier to be reasonable, it must be cost-effective (not cost more than $50,000 per protected residence); and the maintenance, constructibility, drainage and utility impacts, as well as the desires of the affected residents, must be considered. 6 7

5 Sound Principles about Tra f f i c Noi s e Traffic Noise Generation When a sound source is stationary, it is called a point source and it radiates sound equally in all directions like a pulsing sphere. When many sound sources are moving in a line, the sound radiates like a pulsing cylinder from the sources. Traffic noise is generated in this fashion (see graphic on opposite page). It is important to distinguish point sources from line sources because each has different characteristics. Noise is rated on a decibel scale. This scale was designed to match our hearing mechanism and does not work the same as most other familiar scales. A sound that increases by 10 decibels is said to double in loudness. Therefore, a source will sound twice as loud if its level increases from 60 to 70 decibels and four times as loud if its level increases from 60 to 80 decibels. When the number of sound sources is doubled such as two honking horns instead of one the noise level increases by 3 decibels. A 3 decibel change is barely noticeable to most people. Since we don t have the same sensitivity to all frequencies or pitches, the A-weighted scale was developed, and is used for highway traffic noise evaluation. We have included the chart on the right to help you understand the A-weighted decibel scale. For additional information about how traffic noise is measured and analyzed, you can direct your questions to the team involved with the highway project that concerns you. Sound Pressure Levels for Common Sources db(a) Perception of Loudness Sound Source 10 1/16 as loud as 50 db(a) Normal breathing 20 1/8 as loud as 50 db(a) Broadcast studio 30 1/4 as loud as 50 db(a) Library 40 1/2 as loud as 50 db(a) Refrigerator 50 Reference level Clothes dryer 60 2 times louder than 50 db(a) Air conditioning unit 70 4 times louder than 50 db(a) Pick-up 50mph, times louder than 50 db(a) Medium 50mph, times louder than 50 db(a) 50 mph, times louder than 50 db(a) Jet 1000 Point Source Line Source 8 9

6 Traffic Noise Sources The principal noise sources of highway vehicles are the exhaust system, engine, and tires. Exhaust noise is typically controlled by mufflers, assuming they are used and are functioning properly. Engine noise can only be controlled by vehicle manufacturers and proper maintenance, factors that PENNDOT has no control over. Tire noise is generated by the interaction of each vehicle s tires with the road surface. Engine and exhaust noise are usually louder than tire noise at vehicular speeds under 30 miles per hour. The reverse is normally true for vehicular speeds over 30 miles per hour. Highways are typically dominated by tire noise while local streets are typically dominated by engine and exhaust noise. Traffic Noise Propagation The travel, or propagation, of traffic noise depends mainly on three factors atmospheric effects, ground effects, and spreading effects. Atmospheric conditions change the direction of sound travel and constantly change. Ground conditions also affect sound travel. Sound will travel farther over a hard reflective surface than one covered with vegetation. Spreading effects diminish sound at a constant rate as the sound travels away from its source. Sound from a line source such as a highway decreases at a rate of approximately 3 db(a) per doubling of distance from the source. The overall noise level generated by vehicles on a highway depends on the number of vehicles, the speed of the vehicles, and the types of vehicles. The figures below show generally how these factors influence noise levels. How Speed Affects Traffic Noise How Trucks Affect Traffic Noise How Traffic Volume Affects Noise 10 11

7 Managing Our Enviro n m e n t : Traffic Noise A b a t e m e n t Principles of Outdoor Sound Control When trying to solve a noise problem, we look for practical solutions in terms of treating the source of the noise, and the path between the noise source and the listener. Since the source of traffic noise is the combination of vehicles on a highway, the only practical option is to try to reduce the noise along the path between the highway and the listeners. The most common outdoor noise reduction method is the construction of noise barriers. These barriers can take different forms, as long as they break the line-of-sight between the vehicles on the highway and affected residential communities. Barriers can be in the form of walls or topographical changes. Topographical changes can occur by building earth berms or hills between the highway and the communities or by depressing the highway. To be effective, any noise barrier must be solid. Fences or vegetation have minimal effectiveness as noise barriers. Because noise barriers are open to the air above and around them, sound bends over and around them just as light bends around obstructions through the principle of diffraction. Diffraction limits the effectiveness of any barrier to a maximum noise reduction of 10 to 15 decibels, independent of the material used. Typical reductions usually range from 5 to 10 decibels. Parallel Barriers A barrier can be reflective or absorptive, depending on the material used. Reflective barriers can diminish noise reduction capabilities when barriers are on both sides of a highway and are spaced closer than 100 feet apart. In these cases, traffic noise can reflect off of opposite sides as is shown on the illustration above to reduce their effectiveness by up to 3 decibels. In such cases, the use of absorptive barrier faces can reduce the unwanted reflected sound

8 Land Use Planning Measures for Noise Abatement Another option for controlling traffic noise is to use administrative controls available through municipalities. Zoning regulations can be drafted by municipalities to prohibit the development of noise-sensitive locations within specified distances of a highway. Residential developments can also be planned with buffer zones between highways and residential buildings. These buffer zones can be commercial, industrial or undeveloped areas. Although vegetation provides little sound reduction, it can provide a visual screen from a highway. Berms can be designed into developments that visually shield residences from a highway while also providing substantial noise reduction. Alternatives to Noise Barriers Pavement design Research is being conducted on the effect of pavement type on noise generation. Although there is no question that the roadway surface can affect the level of noise generated by vehicle tires, much work still remains to be done to define these effects. Traffic management/speed restrictions Traffic noise levels depend greatly on the types of vehicles on the highway and their speeds. Trucks generate more noise than cars, especially when accelerating and decelerating. Noise can thus be minimized by restricting trucks from certain roadways, enforcing speed restrictions, and minimizing or synchronizing traffic signals. Highway design options Highway design options to minimize traffic noise include building roadways as far as possible from noise-sensitive locations, depressing roadways, and avoiding steep inclines in roadways. Building highways several hundred feet from noise-sensitive locations will minimize noise exposure. Where this is impractical, highways can be built closer to areas that are not noise-sensitive, such as industrial areas. Building highways below ground level creates natural barriers between the highways and any noisesensitive locations. Steep inclines in roadways cause more noise to be generated by vehicles, especially trucks, as they accelerate uphill and decelerate downhill. A level roadway elevation avoids this extra noise generation. Building insulation Sound insulation in buildings, in the form of replacing windows and doors, providing central ventilating systems, and adding insulation to attics, are only considered for public buildings and nonprofit institutional structures on a case-by-case basis

9 Noise Barriers and Other Abatement Options Available in Pennsylvania In Pennsylvania, the noise abatement options considered most often are alternative highway designs and noise barrier construction. Designs that would minimize noise while not compromising safety and practicality are incorporated into highway plans. PENNDOT only uses noise barriers that have been approved through a rigorous product evaluation process to ensure safety, integrity, longevity, and preservation of aesthetics. The following pictures show some of the several different types of noise mitigation options PENNDOT has available. Consult the local PENNDOT Engineering District for color and texture availability in your area. Earth Berm Concrete Wood Other materials such as steel, fiberglass and recycled materials Absorptive Examples of cost-effective barriers in Pennsylvania 16 17

10 Barriers in Your Backyard Measures That Provide Other Benefits Sometimes, building noise barriers and noise minimizing highway designs would not be practical or could not meet established performance criteria. In these cases, PENNDOT cannot provide noise abatement for noise-sensitive areas. Communities still have options to improve these situations; however, PENNDOT is not in the position to fund such options. These include natural screens, man-made screens, and masking systems. Natural screens would be comprised of trees, bushes, hedges, or any visual obstruction to the highway from noise-sensitive locations. Man-made screens would be comprised of materials that have air gaps in them (such as fences) but provide a visual obstruction to the highway. Masking systems add pleasing sounds to the environment to cover up the highway noise. Construction of Noise Barriers The actual cost of noise barriers can often be more than $2 million a mile under normal conditions and can become more than $3 million a mile if noise walls have to be placed on bridges or involve other special designs, such as retaining walls. The costs to the impacted community for the installation of a noise barrier may include some loss to back yard area due to the need to acquire right-of-way to construct the barrier. If there are trees growing in the area where the noise barrier will be constructed, it is most likely that they will have to be removed to accommodate the construction. However, efforts will be made to save as many trees as possible. Generally speaking, it is best to locate noise barriers as close as possible to either the highway or the impacted community to be most effective. Either way, the barriers will be built on PENNDOT owned right-of-way and will be the property of the Department. Maintenance of Noise Barriers The maintenance of noise barriers is the responsibility of PENNDOT. There may be some restrictions to building permanent structures in the area between the noise barrier and private homes, so that PENNDOT may gain access to the residential side of the barrier to perform occasional maintenance or replace damaged panels. Generally speaking, the Department does not provide landscaping on the residential side; however, if homeowners wish to maintain the area between the barrier and their homes, they are encouraged to discuss their plans with PENNDOT

11 How can I get more information about PENNDOT s noise policy? For more information about PENNDOT s noise abatement policy and how it is applied, or about how noise is perceived, measured and controlled, contact your local PENNDOT engineering district or log on to PENNDOT s website at PENNDOT Publication #21 July 2003 Edition