The Environmental Process
The Federal Aid Highway Act of 1962 (FAHA62) required continuing, cooperative and comprehensive
effort during project development and is often referred to as the 3-C process. FAHA62 is significant in
that a public involvement process was begun, which is now ingrained in transportation planning.
The cornerstone of the present environmental legislation is the National Environmental Policy Act
(NEPA). NEPA was passed in 1969 and became effective in 1970. In a very short and succinct piece of
legislation, NEPA declares a national policy that each generation is the trustees of our environment and
is charged with the responsibility of minimizing anthropogenic impacts to the environment to preserve
our resources for future generations. To accomplish this charge, Section 102 required a systematic,
interdisciplinary approach to ensure an integrated approach of natural and social sciences to allow
informed planning and decision-making. Detailed documentation was also required which led to the
birth of the environmental impact statement (EIS). The EIS evaluation required the analysis of:
1. Impacts
2. Unavoidable impacts
3. Alternatives
4. Short term use vs. long term productivity
5. Irretrievable use of resources
An EIS has to be prepared for any Federal project, policy or program implementation. The environmental
assessment process is often called the NEPA process. Subsequent legislation, such as the Federal Aid
Highway Act of 1970 (FAHA70) for highways, has implemented NEPA requirements for all major
transportation projects participating in federal funding.
The NEPA process requires the impacts to be compared to accepted criteria and recommend mitigation
where needed. This has led to a requirement for mathematical models, evaluation methodologies, and
exact reporting procedures. Regulations have been promulgated to define these required processes as well
as measures to be used to mitigate impacts, and guidelines for public participation.
In addition to the NEPA process, other formalized processes, such as conformity (air quality), 404
permitting (water), and 4f determination (land use), may be required during transportation planning.
Various goals for each of these processes can make planning difficult.This myriad of laws and regulations
acts to protect the environment and has formed our present system. A brief summary of the major
federal laws and regulations are presented by environmental topic in the following sections.
Fundamental Concepts and Legal Requirements
Negative environmental externalities have occurred as humankind’s mobility has increased. These undesirable
impacts from transportation include physical impacts (noise, air pollution, water pollution, and
effects on ecology) as well as sociological impacts (archeological impacts, displacements, monetary
impacts, etc.). If transportation projects are to be completed, it is important to understand the nature
of these impacts and the required analysis techniques. Physical impacts are primarily described in this
chapter, with an emphasis on noise and air pollution.
Transportation Noise
Fundamental Concepts of Sound
The perception of sound by an individual — whether it is from a tuning fork producing a pure tone or
the complicated spectra from traffic noise — is an amazing process. The individual evaluates the sound
by at least four distinct criteria. These are loudness, frequency, duration, and subjectivity.
Loudness
.
The loudness or intensity of the noise is directly related to the amplitude of the pressure
fluctuations transmitting through the air. The pressure fluctuations cause the ear drum to be flexed and
create the sensation of sound. The ear can sense pressure fluctuations as low as 2
¥
10
–5
newtons per
square meter (the threshold of hearing) and up to about 63 newtons per square meter, which is considered
the threshold of pain. This represents a pressure change of over 10,000,000 units! Figure 67.1 shows
typical sound pressure levels
This large range of pressure fluctuations is clumsy to use in reporting. Also, as a protective mechanism,
the auditory response is not linearly related to pressure fluctuations.
1
To overcome these two problems,
a human-made unit to describe loudness is used — the decibel (dB) (see Fig. 67.1). The decibel is
computed mathematically by:
where
p
o
= the reference pressure (2
¥
10
–5
newtons/m
2
)
p
= the sound pressure of concern
The use of dB indicates the loudness is measured as a sound pressure level (SPL) and no longer just the
sound pressure.
COMMON OUTDOOR NOISES
Sound Sound
Pressure Pressure
(μ Pa)
(d B)
Jet Flyover at 300 m
Gas Lawn Mower at 1 m
Diesel Truck at 15 m
Noisy Urban Daytime
Gas Lawn Mower at 30 m
Commercial Area
Quiet Urban Daytime
Quiet Urban Nighttime
Quiet Rural Nighttime
Quiet Suburban Nighttime
Level COMMON INDOOR NOISES
Rock Band at 5 m
Inside Subway Train (New York)
Food Blender at 1 m
Garbage disposal at 1 m
Shouting at 1 m
Vacuum Cleaner at 3 m
Normal Speech at 1 m
Large Business Office
Dishwasher Next Room
Small Theatre, Large Conference Room
(Background)
Library
Bedroom at Night
Concert Hall (Background)
Broadcast and Recording Studio
Threshold of Hearing
6,324,555
2,000,000
632,456
200,000
63,246
20,000
6,325
2,000
632
200
63
20 0
In outdoor situations, a change of greater than 3 dB is required to be noticeable. A change of 10 dB
is generally perceived to be a doubling of the sound level. This means that a significant change in
transportation patterns (vehicle volume, speed, mix, etc.) or alignment must occur for individuals to
objectively
determine a change in noise levels.
Frequency
.
The human ear can hear a large range of frequencies, or changes in the rate of pressure
fluctuations in the air. The pressure changes per second, or oscillations per second, have the unit of Hertz
(Hz). The ear can detect a range of frequencies extending from about 20 Hz to 20,000 Hz. It is these
differences in the rate of the pressure fluctuations that provide the tonal quality of the sound and permit
identification of the source. A flute has a much higher frequency than a bass guitar and we are adept
enough to easily tell the difference, just as we can discern aircraft sounds from the blowing wind.
Frequency, the wavelength of the sound wave, and the speed of sound are all related. Mathematically:
where
f
= frequency (Hz)
c
= speed of sound (~343 m/s)
l
= wavelength (distance)
The human ear does not detect all frequencies equally well. Low frequencies (less than 500 Hz) and
higher frequencies (greater than 10,000 Hz) are not heard very well. This requires a sound to be described
by more than just loudness, by including some description of the frequency spectra. The loudness of
each frequency could be reported and evaluated, but this is not practical. Groups of frequencies, called
octave bands, are used to describe sounds and provide a detailed description of the frequency components
(see Table 67.1). However, in regards to transportation sounds, a broader approach is most often used.
In this approach, all frequency band contributions are first adjusted to approximate the way the ear hears
each range, then the contributions are summed to a single number. Three common scales have been
used. Figure 67.3 shows the A, B, and C weighting scales. The A scale is the way our ears respond to
moderate sounds, the B scale is the response curve for more intense sound, and the C scale is the way
our ears would respond to very loud sounds. The non-linear response of the ear at low and high
frequencies is quite apparent from these graphs. Most regulations and evaluations applicable to transportation
analysis use the A scale.
The Federal Aid Highway Act of 1962 (FAHA62) required continuing, cooperative and comprehensive
effort during project development and is often referred to as the 3-C process. FAHA62 is significant in
that a public involvement process was begun, which is now ingrained in transportation planning.
The cornerstone of the present environmental legislation is the National Environmental Policy Act
(NEPA). NEPA was passed in 1969 and became effective in 1970. In a very short and succinct piece of
legislation, NEPA declares a national policy that each generation is the trustees of our environment and
is charged with the responsibility of minimizing anthropogenic impacts to the environment to preserve
our resources for future generations. To accomplish this charge, Section 102 required a systematic,
interdisciplinary approach to ensure an integrated approach of natural and social sciences to allow
informed planning and decision-making. Detailed documentation was also required which led to the
birth of the environmental impact statement (EIS). The EIS evaluation required the analysis of:
1. Impacts
2. Unavoidable impacts
3. Alternatives
4. Short term use vs. long term productivity
5. Irretrievable use of resources
An EIS has to be prepared for any Federal project, policy or program implementation. The environmental
assessment process is often called the NEPA process. Subsequent legislation, such as the Federal Aid
Highway Act of 1970 (FAHA70) for highways, has implemented NEPA requirements for all major
transportation projects participating in federal funding.
The NEPA process requires the impacts to be compared to accepted criteria and recommend mitigation
where needed. This has led to a requirement for mathematical models, evaluation methodologies, and
exact reporting procedures. Regulations have been promulgated to define these required processes as well
as measures to be used to mitigate impacts, and guidelines for public participation.
In addition to the NEPA process, other formalized processes, such as conformity (air quality), 404
permitting (water), and 4f determination (land use), may be required during transportation planning.
Various goals for each of these processes can make planning difficult.This myriad of laws and regulations
acts to protect the environment and has formed our present system. A brief summary of the major
federal laws and regulations are presented by environmental topic in the following sections.
Fundamental Concepts and Legal Requirements
Negative environmental externalities have occurred as humankind’s mobility has increased. These undesirable
impacts from transportation include physical impacts (noise, air pollution, water pollution, and
effects on ecology) as well as sociological impacts (archeological impacts, displacements, monetary
impacts, etc.). If transportation projects are to be completed, it is important to understand the nature
of these impacts and the required analysis techniques. Physical impacts are primarily described in this
chapter, with an emphasis on noise and air pollution.
Transportation Noise
Fundamental Concepts of Sound
The perception of sound by an individual — whether it is from a tuning fork producing a pure tone or
the complicated spectra from traffic noise — is an amazing process. The individual evaluates the sound
by at least four distinct criteria. These are loudness, frequency, duration, and subjectivity.
Loudness
.
The loudness or intensity of the noise is directly related to the amplitude of the pressure
fluctuations transmitting through the air. The pressure fluctuations cause the ear drum to be flexed and
create the sensation of sound. The ear can sense pressure fluctuations as low as 2
¥
10
–5
newtons per
square meter (the threshold of hearing) and up to about 63 newtons per square meter, which is considered
the threshold of pain. This represents a pressure change of over 10,000,000 units! Figure 67.1 shows
typical sound pressure levels
This large range of pressure fluctuations is clumsy to use in reporting. Also, as a protective mechanism,
the auditory response is not linearly related to pressure fluctuations.
1
To overcome these two problems,
a human-made unit to describe loudness is used — the decibel (dB) (see Fig. 67.1). The decibel is
computed mathematically by:
where
p
o
= the reference pressure (2
¥
10
–5
newtons/m
2
)
p
= the sound pressure of concern
The use of dB indicates the loudness is measured as a sound pressure level (SPL) and no longer just the
sound pressure.
COMMON OUTDOOR NOISES
Sound Sound
Pressure Pressure
(μ Pa)
(d B)
Jet Flyover at 300 m
Gas Lawn Mower at 1 m
Diesel Truck at 15 m
Noisy Urban Daytime
Gas Lawn Mower at 30 m
Commercial Area
Quiet Urban Daytime
Quiet Urban Nighttime
Quiet Rural Nighttime
Quiet Suburban Nighttime
Level COMMON INDOOR NOISES
Rock Band at 5 m
Inside Subway Train (New York)
Food Blender at 1 m
Garbage disposal at 1 m
Shouting at 1 m
Vacuum Cleaner at 3 m
Normal Speech at 1 m
Large Business Office
Dishwasher Next Room
Small Theatre, Large Conference Room
(Background)
Library
Bedroom at Night
Concert Hall (Background)
Broadcast and Recording Studio
Threshold of Hearing
6,324,555
2,000,000
632,456
200,000
63,246
20,000
6,325
2,000
632
200
63
20 0
In outdoor situations, a change of greater than 3 dB is required to be noticeable. A change of 10 dB
is generally perceived to be a doubling of the sound level. This means that a significant change in
transportation patterns (vehicle volume, speed, mix, etc.) or alignment must occur for individuals to
objectively
determine a change in noise levels.
Frequency
.
The human ear can hear a large range of frequencies, or changes in the rate of pressure
fluctuations in the air. The pressure changes per second, or oscillations per second, have the unit of Hertz
(Hz). The ear can detect a range of frequencies extending from about 20 Hz to 20,000 Hz. It is these
differences in the rate of the pressure fluctuations that provide the tonal quality of the sound and permit
identification of the source. A flute has a much higher frequency than a bass guitar and we are adept
enough to easily tell the difference, just as we can discern aircraft sounds from the blowing wind.
Frequency, the wavelength of the sound wave, and the speed of sound are all related. Mathematically:
where
f
= frequency (Hz)
c
= speed of sound (~343 m/s)
l
= wavelength (distance)
The human ear does not detect all frequencies equally well. Low frequencies (less than 500 Hz) and
higher frequencies (greater than 10,000 Hz) are not heard very well. This requires a sound to be described
by more than just loudness, by including some description of the frequency spectra. The loudness of
each frequency could be reported and evaluated, but this is not practical. Groups of frequencies, called
octave bands, are used to describe sounds and provide a detailed description of the frequency components
(see Table 67.1). However, in regards to transportation sounds, a broader approach is most often used.
In this approach, all frequency band contributions are first adjusted to approximate the way the ear hears
each range, then the contributions are summed to a single number. Three common scales have been
used. Figure 67.3 shows the A, B, and C weighting scales. The A scale is the way our ears respond to
moderate sounds, the B scale is the response curve for more intense sound, and the C scale is the way
our ears would respond to very loud sounds. The non-linear response of the ear at low and high
frequencies is quite apparent from these graphs. Most regulations and evaluations applicable to transportation
analysis use the A scale.
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