of noise, pollution, and vibrations on plaintiffs’ property” devalued their homes (Denver Post, 1997).
In 2005 the developer of a $1.5 billion project called High Point near DIA planned to build the first of 3,000 homes about 2.5 miles from the end of a planned runway, making future noise complaints almost inevitable (Denver Post, 2005). Buyers were warned they would be moving into an area under aircraft flight paths, but demand for the homes was expected to be high. To protect buyers, homes were built with triple-pane windows, extra insulation, and central air conditioning.
A report in 2005 prepared by DIA’s noise consultants showed that a fully constructed airport would put a noise limit line that would serve as a barrier to residential development right through the High Point project (Denver Post, 2005). The Denver City Council was concerned that occupants of the 3,000 homes in High Point might exert enough political pressure to keep the airport from being completed as envisioned.
More recently, the Denver International Airport Partnership has followed other airports (such as Washington Dulles International Airport) in providing guidelines for prospective homeowners about future development at the airport to head off potential problems (Denver Post, 2006). When DIA is fully built, it could expand from handling 43 million passengers in 2005 to more than 120 million passengers annually.
In 2006 about 320,000 people lived within 15 miles of the airport, and by 2030 the same zone is expected to have more than 500,000 people, according to the Denver Regional Council of Governments (Denver Post, 2006). Contracts for homes near the airport include a legal disclosure that buyers must sign, and some include easements for overhead traffic, precluding residents from suing because of aircraft noise.
The “East Coast Plan” developed by the FAA in 1987 to reduce flight delays changed flight paths across southern New Jersey and dispersed them over a larger area of the state. The plan affected small communities that had complained, not about high levels of noise but about the presence of a few aircraft where none had been previously. This is a good example of communities finding low levels of noise objectionable, when even lower levels existed before a change in policy.
Corbisier (2003) states that “according to the most recent data available from 1987, noise from highway traffic affects more than 18 million people in the United States.” This illustrates both the extent of highway traffic noise and the fact that it has been many years since a systematic study of such noise has been done. It is more difficult to assess the impact of railway noise (see Chapter 5). A reasonable estimate is that 10 million people are affected by railway noise, including 6.5 million by train horns at rail/highway crossings.
The current solution to specific vehicle noise emission problems on highways is to construct noise barriers—solid obstructions built between a highway and nearby homes. Effective barriers can reduce noise levels by 10 to 15 dB, cutting the loudness of traffic noise approximately in half (10 dB) for people who live in close proximity to the barrier. A barrier can be a mound of earth along the side of the road (an earth berm), a relatively high vertical wall, or an earth berm combined with a shorter vertical wall above. Earth berms can be attractively landscaped but require large land areas at the base on both sides of the barrier configuration. Walls are limited to about 8 meters in height and can be made of wood, stucco, concrete, masonry, metal, or other materials.
There are no Federal Highway Administration (FHWA) requirements for the type of material used in the construction of noise barriers. Materials are chosen by the state highway administration but must meet FHWA specifications in terms of rigidity and density. Whatever material is chosen must be rigid enough and of sufficient density to provide a transmission reduction of 10 dB compared with the noise diffracted over the top of the barrier.
FHWA uses the following additional criteria for determining the feasibility of noise barriers: a barrier must be high enough and long enough to block the view of the road; noise barriers do very little good for homes on a hillside overlooking a road or for buildings that rise above the barrier; a noise barrier can achieve a 5-dB noise reduction when it is tall enough to break the line of sight from the highway, and it can achieve an additional 1.5 dB of noise reduction for every meter of height above the line of sight (with a maximum theoretical total reduction of 20 dB). FHWA’s rule of thumb is that a barrier should extend four times as far in each direction as the distance from the receiver to the barrier. Disruptions in noise walls for driveways or street intersections destroy their effectiveness. Moreover, in some areas, where homes are far apart, the cost of a barrier may be prohibitive.
The construction of noise barriers has always been a cooperative effort between state departments of transportation and FHWA, and states have a great deal of flexibility in designing and building noise barriers. Some states have built many noise barriers, and some have built none. Through the end of 2004, 45 state departments of transportation and the Commonwealth of Puerto Rico had constructed more than 2,205 linear miles of barriers at a cost of more than $2.6 billion ($3.4 billion in 2004 dollars). Five states and the District of Columbia have not constructed any noise barriers (FHWA, 2009).
Noise barriers tend to provide relief for a relatively small number of people in a given area, but the noise reductions are probably greater than those that could be achieved with modern pavement technology. However, the number of people