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Federal Highway Administration Research and Technology
Coordinating, Developing, and Delivering Highway Transportation Innovations
This magazine is an archived publication and may contain dated technical, contact, and link information.
|Publication Number: Date: May/June 2003|
Issue No: Vol. 66 No. 6
Date: May/June 2003
States share successful strategies for partnering with the public to design aesthetically pleasing noise barriers.
Lizards, cacti, ladybugs, trees, leaves, animal tracks, and mountain scenes. No, this is not a list of topics in a textbook on ecology. Rather, these items are design elements adorning highway barriers constructed to decrease noise from traffic.
|On the residential side of this noise barrier in Scottsdale, AZ, detailed design treatments and landscaping with native desert plants create an appealing pedestrian environment for people like this walker and jogger.|
In the past, transportation agencies focused on ensuring that barriers reduce noise, but in recent years designers have given increased attention to the aesthetic qualities of these walls—and for good reason. According to Bob Armstrong, leader of the Noise Team in the Federal Highway Administration's (FHWA) Office of Natural and Human Environment, aesthetics are just as important—maybe even more important—than the noise reduction capacity of a barrier. "Many citizens," Armstrong says, "view an ugly barrier as a waste of time and money and are likely to say that it doesn't reduce noise."
The most successful highway noise barriers complement their surroundings, while performing their intended acoustical functions. The barrier's size, shape, materials, texture, treatments, and context all contribute to how the wall looks to motorists and community members alike.
Across the country, designers are involving the public in making decisions about the look and feel of existing and new barriers. Whether jagged, stepped, sloped, uniform, irregular, colored, plain, straight, curved, or textured, today's most aesthetically successful barriers reflect the local flavor of their communities and enhance the quality of the transportation environment.
An Introduction to Noise Barriers
Highway traffic noise is an important concern for communities across America. Emanating from vehicle engines, exhaust systems, and tires interacting with pavement, traffic noise affects the quality of life for nearby residents and businesses by drowning out conversations, disrupting sleep, and discouraging outdoor activities.
FHWA outlined a three-pronged approach to controlling highway traffic noise. Quieting the source—vehicles—is one approach. Since passage of the Federal Noise Control Act of 1972, trucks and tires have become quieter. A more recent approach, noise-compatible land use planning, seeks to eliminate or reduce the undesirable effects of traffic noise by encouraging the location of less noise-sensitive land uses near highways and promoting the use of open space or special building construction techniques to minimize the impact of traffic noise.
Mitigation of noise from highway projects, most commonly the construction of noise barriers—solid obstructions built between a highway and nearby homes and businesses—represents the third strategy for reducing highway noise. Barriers reduce the noise from a busy highway, reflecting it back across the highway, or forcing it to take a longer path over and around the barrier. In most cases, noise barriers also serve as privacy screens, blocking motorists' views of nearby homes and creating privacy for residents.
Engineers measure the magnitude of noise in decibels (dB). A value of 0 dB corresponds to the threshold of hearing for most humans, while highway traffic rates about 65-75 dB. Although noise barriers do not block all noise completely, they do reduce overall noise levels—typically by 5 to 10 decibels—effectively cutting the loudness of traffic noise by up to one half. For example, a barrier that reduces noise by 10 dB reduces the sound level of a typical tractor trailer to that of an automobile.
To reduce sound transmission through a barrier effectively, the material chosen for a noise barrier must be rigid and dense—at least 20 kilograms per square meter (4.1 pounds per square foot). At this density, all the common materials used to construct noise barriers—concrete, masonry block, brick, wood, metal, earth berms, etc.—are equally effective acoustically. Federal guidelines do not specify which material to use; rather, individual State DOTs select the material based on factors such as aesthetics, durability, cost, and maintenance.
Nearby residents' perceptions of the effectiveness of noise barriers typically vary. For example, a barrier may provide a full 10-dB reduction, but if the noise levels are still near 66 or 67 dB, residents may judge the barrier "ineffective" or "no better than before." Perceptions also may relate to nonacoustical factors, such as how the barrier fits into the human or natural environment. In designing a barrier, agencies consider such factors as the proximity of the barrier to residences (generally trying to provide a distance of four times the barrier's height), the barrier's visual impact on the surrounding area (which can be improved by aesthetic treatments or landscaping with native plants), and drainage issues (which can be addressed by accommodating water flow along or beneath the barrier).
In August 2000, FHWA published the updated Highway Noise Barrier Design Handbook, a state-of-the-art reference manual available online and on CD-ROM. The handbook covers concepts, designs, materials, and installation techniques for highway noise barriers. To access the manual or learn more about noise barriers, visit www.fhwa.dot.gov/environment/noise/manual.htm. Copies of the CD-ROM may be purchased through the National Technical Information Service by calling 800-553-6847 or e-mailing email@example.com.
Noise, defined as unwanted or excessive sound, is an undesirable byproduct of modern life. Although noise emanates from many different sources, noise from highway traffic is among the most pervasive and difficult to avoid.
Traffic noise has been a Federal, State, and local concern since the 1960s, and the first noise barrier was built in 1963 in Washington State. In 1976, FHWA developed the first Highway Noise Barrier Design Handbook to help State highway agencies address all the considerations in noise barrier design appropriately. In the two decades since FHWA published the handbook, substantial advancements have occurred in all elements of barrier design. Further, increased community and motorist interest has fueled the push to provide less expensive and more aesthetically pleasing and environmentally friendly barrier designs.
With highway construction projects often located near existing residential and commercial environments, barriers are by far the most common technique for reducing the impacts of traffic noise. In 2000, FHWA's Noise Team gathered information from State departments of transportation (DOTs) to assess the extent of noise barrier construction. The team concluded that, as of 1998, 44 State DOTs and the Commonwealth of Puerto Rico had constructed more than 2,610 kilometers (1,620 miles) of barriers at a cost of more than $1.9 billion (in 1998 dollars).
The survey also revealed that most barriers are constructed from concrete or masonry block, although other building materials include wood, metal, earth berms, brick, recycled materials (such as plastics and composite polymers), or combinations of these materials. In general, barrier dimensions range from 3 to 5 meters (10 to 16 feet) in height, and the average cost ranges from $175 to $200 per square meter ($16-19 per square foot). To see more results from FHWA's survey, "Summary of Noise Barriers Constructed by December 31, 1998," visit www.fhwa.dot.gov/environment/bar98txt.pdf.
Most roads and streets (97 percent) in the United States fall under the jurisdiction of State and local governments. Federal jurisdiction is limited mainly to national parks, national forests, and other government-owned lands. According to FHWA noise regulations, each State DOT has the flexibility to determine the need for noise abatement on streets and highways—and its feasibility—and to balance the benefits of abatement measures with the social, economic, and environmental costs. Federal noise regulations—found in Title 23 of the U.S. Code of Federal Regulations, Part 772, "Procedures for Abatement of Highway Traffic Noise and Construction Noise"—apply to projects where a State DOT requests Federal funding for participation in the improvements.
According to Armstrong, advance planning and shared decisionmaking are the best ways to ensure that a noise barrier meets the needs of the community, the motoring public, and the transportation agency. Armstrong emphasizes the need to think consciously about aesthetics during project planning, with input from a multidisciplinary team, including landscape architects, noise engineers, and the community.
"An ugly barrier isn't going to sell," Armstrong says. "You can spend a lot of money, but if you put up a barrier people don't like, you're going to have a problem. States can gain public acceptance for noise barriers by getting community buy-in—and sometimes communities even volunteer to contribute money for special aesthetic treatments. They often see public involvement as a plus because they have a say in what is going into their backyards."
A sampling of barrier projects from Arizona, Pennsylvania, and Washington State offers insights into the strategies that have proven successful at solving noise problems, while satisfying community concerns about the visual impact of noise barriers.
U.S. Route 202 is a heavily traveled and densely populated highway corridor in southeastern Pennsylvania. As the Pennsylvania Department of Transportation (PENNDOT) began planning to widen the highway to six lanes in the early 1990s, the agency conducted environmental studies to determine the sections along the corridor where construction of noise barriers might be appropriate.
|Shrubs and freshly cut grass complement a tree motif on the noise barrier along U.S. Route 202 in Tredyffrin Township, PA.|
According to Bob Keller, environmental manager for PENNDOT Engineering District 6, the final noise study identified the segments where barriers were warranted, feasible, and reasonable, and then his staff presented their findings to the community.
"Our policy is that we meet with all the communities that will be affected by the highway project to present the results of the noise study," says Keller. "In the first part of the meeting, we explain that PENNDOT will not build the barrier unless the community wants it. I've been doing this job for 30 years, and no one has ever rejected our offer to install a noise wall."
In the second part of the meeting, Keller and his staff explain the community's options for enhancing the aesthetics of the wall. "We like to give the community patterns to choose from," Keller says, "like going to the paint store."
PENNDOT usually focuses aesthetic treatments on the residential side of its noise walls; however, in Tredyffrin Township, the residents wanted to do more. Seeking to use the walls as a symbolic gateway to the township, residents elected to add a treatment to the highway side of the wall as well. PENNDOT and the township worked together on the design, and the township agreed to cover the extra costs for the highway-facing treatment. In consultation with PENNDOT's concrete fabricator, the township eventually settled on a tree design to face onto the highway.
Keller says the key to PENNDOT's success with noise barriers is the open public involvement process. "We have an open door policy," Keller says. "Highway construction projects often take years, and a lot of times we find communities and residential governments turn over fast. So we go back to meet with communities as often as necessary. We also have a brochure that we update with sample noise barrier textures to use as a guide."
Joseph Janasik, Tredyffrin township manager, recommends incorporating considerations for design enhancements into the original construction contract. "You can do a good design for about the same amount as a typical wall," he says. "What made it expensive for us is that we redesigned the wall after the contract was let."
Also important is being upfront with the community in terms of what the walls actually do. "Don't oversell the effectiveness," Keller from PENNDOT says. "Walls are about mitigating, not eliminating, noise. Spend some time at community meetings establishing a common ground and vocabulary so people understand decibels, how we measure noise, and what the noise study results mean. We've received positive feedback from residents for taking the time to educate them at the beginning of the process and answer their questions along the way."
"In the past, we always put cost ahead of aesthetics," says Alex Young, bridge and structures architect at the Washington State Department of Transportation (WSDOT). "But in the last 2 or 3 years, context-sensitive design has become a priority, and WSDOT is putting more emphasis on aesthetics in high-visibility projects, with minimal additional cost."
Sample Costs for Aesthetic Treatments
According to Alex Young, the bridge and structures architect for the Washington State Department of Transportation, the construction cost for installing a concrete noise wall using a rubber form liner custom-designed for an aesthetic treatment is about the same as the cost of using a commercially available rubber form liner.
In Washington State, an off-the-shelf rubber liner, which can be used repeatedly, costs about $323 per square meter ($30 per square foot). The only cost difference for applying an aesthetic treatment comes from creating the master mold for the form liner—which costs about $538/m2 ($50/ft2). Once the master mold is created, the custom-designed form liner costs the same as a commercially available liner.
Given a 9,290-square-meter (100,000-square-foot) precast concrete noise wall composed of 3.7-meter by 3.7-meter (12-foot by 12-foot) panels, the costs would be as follows:
Scenario #1: Precast concrete noise wall using commercially available rubber form liner, installed cost @ $172/m2 ($16/ft2) = $1.6 million.
Scenario #2: Precast concrete noise wall using custom-designed rubber form liner, installed cost (base cost of $1.6 million from Scenario #1 plus $7,000 for the master mold) = $1.607 million.
In 2001, to increase safety and enhance mobility on a heavily
traveled section of State Route 527, WSDOT planned to widen more than 3.2 kilometers (2 miles) of highway through the City of Mill Creek. The completed highway would include two lanes in both directions (with a center turn lane and landscaped medians), in addition to sidewalks and bike lanes. WSDOT planned to install a noise barrier to mitigate the noise that would result from the improvement.
"When we first looked at the plan for the noise wall, it called for the standard fractured-fin treatment," says Cari Hornbein, senior planner for the City of Mill Creek. (A fractured-fin treatment involves mechanically shearing masonry blocks to create a rough, textured surface.) "However, Mill Creek is a small community with a high-quality design aesthetic. The city's development regulations require design approval for noise walls from its Design Review Board, which is concerned with the design of the streetscape along the main thoroughfares. We expressed our concerns to WSDOT, and the agency agreed to explore other options."
|Leaf and tree bark graphics enliven this noise barrier in Mill Creek, WA.|
|Workers sculpt the clay forms for a noise barrier along SR-527 in Mill Creek, WA.|
Hornbein teamed up with FHWA's Alex Young and, from WSDOT, Sally Anderson (landscape architect) and Jeff Lundstrom (project engineer) to serve as the design team for the project. Working together, the team brainstormed ideas for a wall treatment that would reflect the character of Mill Creek. Young took the ideas and developed alternative designs for the city to consider. The designs featured maple and alder leaves, cedar branches, dragonflies, ladybugs, and animal tracks—all natural elements representative of Mill Creek's environmental heritage.
"We have a lot of policies about preserving natural areas and open space," Hornbein says. "Alex came back with a good design that we all felt we could work with."
|Mature fir trees tower above the noise barrier and retaining wall in Mill Creek, WA.|
After gaining approval from the city, Young created three clay relief sculptures. In the final design, the top 1 meter (3 feet) of the noise wall consisted of alternating leaf patterns running the entire length of the wall, while the bottom portion featured a fractured-granite treatment that resembles tree bark.
"It was a productive and community-sensitive process," Hornbein says. "Regarding the completed wall," she adds, "the final product is fabulous. Other cities are interested in using similar designs."
|These close-ups of the noise barrier in Mill Creek feature various leaves and insects, including a dragonfly and ladybug.|
According to Young, additional aesthetic treatments sometimes increase project costs. However, WSDOT case histories show that, in some cases, aesthetic treatments actually cost less to implement than standard finishes. "It's up to each agency to make the call on how much extra to spend," he says. "With a $500,000 noise wall, adding 1 percent or $5,000 isn't bad if special treatment is appropriate for a given location. On this section of SR-527, the speed limit is only 35 miles per hour [65 kilometers per hour], and a sidewalk parallels the wall, so pedestrians and motorists can appreciate the aesthetic improvements."
The SR-527 noise wall was so well received that WSDOT is in the process of designing a similar treatment for the City of Redmond.
In 1996, the Arizona Department of Transportation (ADOT) was preparing to finalize the roadway design on State Loop 101/Pima Freeway through Scottsdale, AZ. Because of limited rights of way and to reduce traffic noise, ADOT planned to build much of the 9.5-kilometer (6-mile) stretch through Scottsdale below grade, creating a concrete corridor with flat surfaces reaching nearly 15 meters (50 feet) high in places as a result of large expanses of bridges, retaining walls, equestrian trail overpasses, and noise barriers.
|A row of bridge piers featuring the same lizard motif used in the noise barriers will help support the new freeway in Scottsdale, AZ.|
Renowned for its thriving arts community, the City of Scottsdale was anxious to preserve its artistic reputation and minimize the impact of the $131 million project on citizens and visitors. City officials approached ADOT to discuss options to enhance the aesthetic quality. Due to budgetary constraints, ADOT could not provide additional funding for aesthetic enhancements beyond the standard treatment but agreed that if the city could raise the money to apply special treatments, ADOT would revise its construction contracts accordingly.
Armed with $5 million in capital improvement funds, city officials and members of the Scottsdale Cultural Council issued a request for proposals to examine the possibilities. The council selected a design team that included local landscape architect Jeff Engelmann, Colorado-based artist Carolyn Braaksma, and local architect Andrea Forman. The team examined the corridor for possible public art opportunities.
|A family enjoys a stroll along the landscaped residential side of the Pima Freeway noise wall in Scottsdale, AZ.|
|Scottsdale's designers created large-scale treatments on the highway-facing side of this noise barrier on the Pima Freeway, creating better views for motorists traveling at highway speeds.|
Engelmann, vice president of J2 Engineering and Environmental
Design, served as project manager of the design team. According to Engelmann, what struck the team was the size and magnitude of the walls, offering an opportunity for public art that would embrace the city's overall ideals and assist in creating an art project that could help weave together a community that was being split by the corridor alignment.
The design team consulted with museum curators and staff from local botanical gardens to discuss images and textures taken from the area's desert ecosystem, and then they gathered community input through public workshops. The team explained the early concepts to the public through exhibitions at local libraries as well as the workshops. The final concept also needed to pass through the city's Design Review Board, since the board approves all public works projects in Scottsdale.
Comparison of Common Barrier Materials
Concrete—Nearly half the noise walls in North America are made from concrete.
Combination Earth Berm and Noise Barrier—An earth berm of soil, stone, rock, or rubble is combined with a noise barrier.
Brick and Masonry Block—A clay-sand mix is fired in a kiln to increase strength and durability.
Wood—Wood noise barriers may be constructed from fir, pine, spruce, and other tree species.
Metal—Steel, aluminum, and stainless steel are the most common metals used in construction.
Source: FHWA's Highway Noise Barrier Design Handbook.
Ultimately, the design team settled on a desert theme that encompasses the area's historical, cultural, and climatic diversity. Elements included cacti, lizards, and other desert flora and fauna; mountains; and a Native American-inspired motif. The team designed the motifs for two environments: fast-moving freeway traffic and slower-paced pedestrian and neighborhood traffic. Textures and patterns on the freeway side are larger for easier viewing and avoiding distraction. They include a 20-meter (67-foot)-tall lizard and 12-meter (40-foot)-tall prickly pear cactus. On the neighborhood side, local trail users and pedestrians enjoy the same motifs, but at a scale and complexity that reflects the slower pedestrian movement.
|This section of the noise barrier on Pima Freeway features stylized prickly pears and mountains. Homes and trees are visible in the background beyond the wall.|
To fabricate the artwork, crews used a cast-in-place technique, pouring concrete into preconstructed vertical molds at the site. "When the contractors saw the form liners, they freaked out," admits Alex McLaren, the construction and design director for the city of Scottsdale, "but the completed project looks fantastic, and they are proud of it."
According to Engelmann, the number one concern of the public community was that the aesthetic treatment would not slow the freeway construction process—and in fact it did not add time because the project used standard construction materials and methods. As long as design is addressed upfront, aesthetic treatments should not add time to the design process either.
|Varying the relief, textures, materials and colors in the design of a noise barrier helps create visual interest, as shown in this detail of a prickly pear cactus on a multi-textured panel.|
Engelmann describes the cost for enhancements as "minimal compared to the cost of the overall project." He offers a number of best practices to ensure the biggest bang for the buck.
Margaret Bruning, associate curator of public art for the Scottsdale Public Art Program, lauds the art installation on the Pima freeway. "On the public level," she says, "you have an artistic treatment that is responsive to the scale of the environment. If you are driving 65 miles per hour down the freeway, it envelops you without being distracting. On another level, the treatment serves as a tool to introduce people to Scottsdale, showing that the city cares about the quality of life for its citizens and visitors driving on the freeway itself. Also, the content of the art is palatable on different levels. You don't need to know a lot about the place or be an art connoisseur to appreciate the design."
"Noise is a people issue," says FHWA's Bob Armstrong, "that affects everyone."
People living near highways relate to noise barriers—and barrier aesthetics have the capacity to determine if that relationship is a positive one. On the one hand, noise barriers minimize excessive traffic noise, improving living and working conditions for nearby residents and businesses. On the other hand, barriers are tall walls that restrict sunlight and air circulation and have the capacity of being visually intrusive.
According to Armstrong, noise barriers represent one way that transportation agencies can involve communities in the highway program. "Citizens often view highway development as being outside their world," he says. "Getting people involved in the decisionmaking process, even if it's as simple as specifying the material color or type of shrubbery to be planted near a noise wall, goes a long way toward building goodwill."
John J. Sullivan IV is a contract writer for FHWA and assistant editor for Public Roads magazine.
For more information about noise barriers, contact Bob Armstrong at 202-366-2073 or firstname.lastname@example.org.