Design Guide For Highway Noise Barriers
Design Guide For Highway Noise Barriers
Design Guide For Highway Noise Barriers
Project conducted in cooperation with the U.S. Department of Transportation, the Federal Highway Administration, and the
Texas Department of Transportation.
16. Abstract
The current TxDOT design process for highway noise barriers is reviewed. Design requirements for highway noise barriers are
then presented. These include acoustical requirements, structural requirements, safety requirements, aesthetic requirements, and
cost considerations. Examples are given of different highway noise barriers used in Texas. Sample plans and specifications are
presented. Design requirements are broadly grouped into acoustical requirements, environmental requirements, traffic safety
requirements, and structural requirements; those requirements are again presented, drawing on the material presented in the
preceding chapters.
17. Key Words 18. Distribution Statement
acoustics, aesthetics, design, noise barriers No restrictions. This document is available to the public through
the National Technical Information Service, Springfield, Virginia
22161.
19. Security Classif. (of report) 20. Security Classif. (of this page) 21. No. of pages 22. Price
Unclassified Unclassified 96
Form DOT F 1700.7 (8-72) Reproduction of completed page authorized
DESIGN GUIDE FOR HIGHWAY NOISE BARRIERS
Richard E. Klingner
Michael T. McNerney
Ilene Busch-Vishniac
November 2003
Implementation Statement
This design guide is intended to provide Texas Department of Transportation (TxDOT) designers
with background information, specific design procedures, and sample plans and specifications
for the design of highway sound walls. TxDOT personnel should use the design procedures
recommended in this Guide.
Disclaimer
The contents of this report reflect the views of the authors, who are responsible for the facts and
the accuracy of the data presented herein. The contents do not necessarily reflect the official
views or policies of the Federal Highway Administration or the Texas Department of
Transportation. This report does not constitute a standard, specification, or regulation.
There was no invention or discovery conceived or first actually reduced to practice in the course
of or under this contract, including any art, method, process, machine, manufacture, design or
composition of matter, or any new and useful improvement thereof, or any variety of plant,
which is or may be patentable under the patent laws of the United States of America or any
foreign country.
Acknowledgments
Research performed in cooperation with the Texas Department of Transportation and the
U.S. Department of Transportation, Federal Highway Administration.
Table of Contents
v
Chapter 4. Safety Considerations in the Design of Noise Barriers.....................................33
Introduction............................................................................................................33
Requirements Related to Vehicular Impact ...........................................................33
References ................................................................................................................................81
vi
List of Figures
vii
viii
List of Tables
ix
x
Preface
When Study 1471 began almost 10 years ago, it was intended to provide general and
specific information to TxDOT personnel regarding almost all aspects of noise barriers:
o software that would help neighborhoods understand the visual and acoustical effects
of hypothetical noise barriers.
Over the first four years of Study 1471’s existence, its deliverables were expanded even
more, to include a study of parallel-barrier reflection. Researchers proposed that the study
deliverables be packaged in separate binders, each dealing with different aspects of the
study. In that format, three study reports were published by TxDOT. The process of
finishing the fourth and final report, and its associated summary report, encountered
unexpected challenges. In the remainder of this Preface, those challenges are discussed,
presented, along with the ways in which they were resolved.
Challenge 1:
Over the course of Study 1471, unforeseen events outside of TxDOT overtook and in some
ways superseded the original deliverables of that project. For example, in February 2000,
FHWA published a comprehensive handbook1 on the design of highway noise barriers.
That handbook contains comprehensive background material on acoustics and the acoustical
functioning of highway noise barriers, and also some background on aesthetics. In the
authors’ opinion, the treatment in that handbook is excellent, and supersedes many of the
needs envisaged by TxDOT for that deliverable from Study 1471. Although the
visualization software developed by Study 1471 would have met needs not addressed by the
1
Knauer, H. S., Pedersen, S., Lee, C. S. Y. and Fleming, G. G., FHWA Highway Noise Barrier Design Handbook (Report
No. FHWA-EP-00-005), US Department of Transportation, Federal Highway Administration, Washington, DC, February
2000.
FHWA handbook, that software was probably not sufficiently user-friendly to be useful to
TxDOT on a day-to-day basis.
Challenge 2:
Over the course of Study 1471’s existence, evolution of TxDOT policies and associated
TxDOT publications led to other ways of addressing many of the areas originally intended
to be addressed by Study 1471 deliverables. Some examples are as follows:
b) Evolution of combined TxDOT and FHWA policies. For historical reasons, TxDOT has
built in the past some types of sound walls (such as those mounted on traffic barriers)
that would probably not be their design choices today. The existence of such walls led
to the inclusion, in draft deliverables for Study 1471, of the performance of mounted
barriers, including structural performance under vehicular impact. In the meantime,
TxDOT's Design Division and the FHWA had determined independently that barrier-
mounted noise barriers were much less viable than other solutions (damage-resistant
lower sections on existing sound walls, or placement of noise barriers behind vehicular
barriers). The evolution of FHWA requirements for crash-testing of barriers also made
moot a discussion of structural design criteria for vehicular impact on sound walls, since
performance under impact would have to be verified by crash testing in any event. As a
result, much of the material developed by Study 1471 dealing with vehicular impact
would not be useful to TxDOT designers today, could be misinterpreted by those
unfamiliar with FHWA criteria, and would not be a useful to include in a Study 1471
deliverable now.
Challenge 3:
Over the course of Study 1471’s existence, unforeseen changes occurred in the professional
affiliations of some Study 1471 researchers. Dr. Michael McNerney left the Center for
Transportation Research for a position in the Dallas area; Prof. Irene Busch-Vishniac left
The University of Texas at Austin to become Dean of Engineering at the Johns Hopkins
University; and other project-specific researchers have graduated or moved on.
2
Guidelines for Analysis and Abatement of Highway Traffic Noise, Texas Department of Transportation, June 1996
(Change 1, July 1997.
In response to these challenges, the researchers of Study 1471 and related TxDOT personnel
have agreed to take the following steps:
o to take those deliverables in Study 1471 that are still relevant, still consistent with
TxDOT policy, and still useful to TxDOT personnel, to augment those deliverables
appropriately, and to package those deliverables in a useful format as Report 1471-4.
Introduction
Highway noise barriers (sometimes referred to as “noise walls” or “sound
walls”) are intended to mitigate the effects of highway noise on activities near
the highway. They do this primarily by blocking the direct path that sound
must travel between the source of sound on the highway and the receiver
exposed to the sound. The terms noise barrier and sound wall are used nearly
interchangeably in this report. Noise barriers are designed for acoustic
performance; they need not specifically be walls. Walls are designed
structurally to withstand their design loads.
Many different noise barrier systems are used in Texas. In Chapter 7, these are
described more completely. Because highway noise barriers that are distinct in
appearance may actually be quite similar in function, it is useful to classify
them. This classification is neither definitive nor unique, and is adopted
primarily for convenience. For purposes of this design guide, noise barrier
systems used in Texas are classified as follows:
Current TxDOT policy is that all highway noise barriers located within the
clear zone must be protected by a separate traffic barrier. If the noise barrier is
integrated with the traffic barrier, it is required to resist vehicular impact. To
meet FHWA guidelines, all such barriers must be crash-tested. In practical
terms, the most effective way to meet these requirements is to put a crash-
tested vehicle impact barrier in front of the noise barrier. Then the noise
barrier itself would not have to be designed for vehicular impact.
1
In the past, some highway noise barriers have been integrated with vehicular
barriers. One example of this is the prefabricated, barrier-mounted, post-and-
panel system that was developed and constructed in the Fort Worth District
(TxDOT 1996). In later sections of this report, that design is discussed.
According to current TxDOT policy, that barrier is no longer recommended.
This is an example of how the design of noise barriers must be integrated with
the design of other related highway elements.
Because each District Office has the authority to implement the design of
noise barriers as the District Engineer decides, a summary of the TxDOT
experience was collected for this design guide. Telephone interviews were
conducted with the Texas Department of Transportation (TxDOT) district
personnel regarding their experience with sound-wall design. This chapter
summarizes and presents the information gathered from those interviews.
The phone interviews were conducted with structural engineers from five
districts that currently have designed and constructed at least one sound wall.
These five districts were the Dallas, Fort Worth, Austin, San Antonio, and
Houston districts. In talking with each engineer, the need for standard design
guidelines became evident.
The interviews focused on three major topics: the process used to select the
sound wall type and material; the structural design procedure; and the major
problems encountered. Each district had different procedures for handling
each of these three topics.
2
Structural Design Process for Sound Walls
The first questions for each survey recipient dealt with the structural design
process; that is the structural design of a sound wall whose existence; height
and length have already been determined by acoustical considerations. All
districts were familiar with the American Association of State Highway and
Transportation Officials (AASHTO) Structural Design Specifications for
Sound Barriers (AASHTO 1992a) and used it as a first reference. Several
other references were cited:
• Load and resistance factor design (LRFD) manual (AISC 1992), American
Concrete Institute (ACI) 318 (ACI 1995), and other material codes
• Other applicable codes such as the Structural Welding Code (AWS 1981)
Some districts noted that the above references did not address some important
design parameters and did not consider all design conditions. In particular, the
districts identified a need for guidelines on the minimum thickness of a free-
standing sound wall, on deflection limits (serviceability), and on vehicular
impact requirements.
In all districts, the structural engineer was responsible for selecting and
developing numerical design parameters and for applying the design. For the
Houston District, the most common sound walls involve proprietary systems.
While the proprietary designers and contractors involved in the construction
of these walls were ultimately responsible for the design, they received
assistance from fabricators, TxDOT engineers (using in-house standards), or
both. In each such case, the TxDOT District Engineer was still required to
approve each project.
Design of a sound wall begins with the determination of its height and
location relative to the roadway. These parameters are dictated by acoustical
requirements, and are determined by the environmental engineer. Once these
parameters have been determined, the structural design of the sound wall can
proceed.
3
for most designs. In Austin and San Antonio, aesthetic considerations
controlled. In Houston, local influences suggested that the sound walls be of
concrete, the primary building material for the region. Overall, the primary
factors determining the final sound wall design varied from project to project
and district to district, making the standard design process difficult to
describe.
Currently, four of the five Texas districts polled have no personnel assigned
specifically to the design of sound walls. Houston has had the most experience
with sound walls and had assigned a permanent staff member (Marc Anthony)
to study sound walls and prepare plans for them. Most projects are handled by
the special project department and are usually a cooperative effort between the
environment and structural engineering departments.
Most sound-wall projects were let and the contractor selected by bid. Some
districts used only prequalified contractors on projects and did not allow the
projects to be bid. In most cases, alternates were allowed to be bid by the
contractors. In such cases, requirements were defined for the alternates. As
with the design criteria, the alternate designs were required to satisfy the most
important design parameters discussed above.
4
for impact, although no formal requirements were specified. While some
districts prefer to strengthen the lower portions of sound barriers to improve
durability, these barriers should never be placed inside the clear zone in lieu of
a traffic barrier. For liability reasons, the language on a standard detail for a
sound wall should never imply that the sound wall is designed as a traffic
barrier. Noise barriers designed for vehicular impact typically must be crash-
tested in accordance with NCHRP 350, Test Level 3, to gain FHWA
acceptance (NCHRP 1993; FHWA 1996b).
5
6
CHAPTER 2
ACOUSTICAL CONSIDERATIONS IN NOISE-BARRIER DESIGN
Measurements of Noise
Sound is a wave. It exerts pressure on the human eardrum and on noise-
measuring instruments. Sound intensity is proportional to the square of the
pressure. Levels of sound (noise) are measured in decibels (dB), a logarithmic
measure of sound intensity. Small changes in dB levels imply large changes in
actual sound intensity. Noise levels expressed in dBA are weighted so that
sound levels are more important if they are at frequencies to which the human
ear is more sensitive. Different dBA levels are described in Table 2.1.
Highway noise levels vary over time. To describe them in terms of a single
number, the concept of equivalent sound level (Lq) has been developed. Leq is
the constant sound level that contains the same average acoustic energy as the
original time-varying sound level.
7
blocked. The required thickness in inches for a 30-dB transmission loss at 100
Hz is given in Table 2.2.
Properties of Sound
8
produce noise in the range of 20 to 2,000 Hz. Trucks produce noise in the
range of 10 to 1,000 Hz. In both cases, the typical sound has a broad peak at
about 125 Hz, but this number is misleading because the ability of humans to
hear sounds is not uniform throughout the audible frequency range. As a result
of the skewing of the sound by our hearing system, typical car and truck noise
has a broad perceptual peak at about 500 Hz. Because speech is concentrated
from about 300 to 3,300 Hz, car and truck noise is quite effective at intruding
on speech, a fact of which we are all painfully aware.
The intensity of a sound is the objective measure of its loudness (subjective
measure). Intensity is a measure of the sound energy. Humans have an ability
to perceive a wide range of sound intensities. Indeed, our hearing range is
significantly broader than that of any of our other senses. Partly because of
this, we use a logarithmic scale for intensity. The specific scale employed is
the decibel or dB, named after Alexander Graham Bell. It is defined as dB =
10 log10 (W/Wref), where W is the sound power or a quantity proportional to
energy (such as intensity or pressure squared), and Wref is a reference sound
power (or intensity or pressure squared) defined as the standard for
comparison. The dB measure is termed a level. If the quantity used is energy,
the result is the sound energy level; if the quantity in the logarithm is
intensity, it is the sound intensity level; if the quantity is pressure squared, the
result is the sound pressure level.
Given this definition, a doubling in the intensity of a sound corresponds to an
increase of 3 dB in the sound level. We do not generally perceive a doubling
of intensity as a doubling in loudness, however. The general rule of thumb is
that a doubling of loudness (in the speech range) corresponds to a 10-dB
increase in intensity; that is, to an increase in the energy by an order of
magnitude. Figure 2.1 shows the sound pressure levels associated with a
variety of situations and sources. The levels are presented in terms of dBA.
Here the “A” indicates that “A-weighting” was used to account for the human
hearing variations as a function of frequency. The dBA scale is accepted
worldwide as the best predictor of human response to sound. Note that the
figure shows that the range of hearing spans orders of magnitude of intensity.
The federally mandated levels at which noise mitigation for residences should
be considered is also shown in the figure.
An important property of sound that plays a key and essential role in noise
barrier operation is called geometrical spreading. Geometrical spreading
refers to the fact that sound, very much like light, reduces in intensity as it
propagates from a source. One can determine the attenuation produced by
geometrical spreading by noting that sound energy is approximately
conserved as the sound spreads from the source. For a source concentrated at a
point in space (a point source), such as shown in Figure 2.2, the sound spreads
uniformly on the surface of a spherical wave front. The total energy of a
source can be found by multiplying the intensity at a set distance from the
source by the area over which that intensity is distributed. Because the surface
area of a sphere increases in proportion to the square of the distance from the
9
center, the energy is proportional to intensity at a point, multiplied by the
square of the distance from the source to that point. Since total energy is
conserved, doubling the distance from d to 2d must result in a drop in
intensity by a factor of four (6 dB). Most traffic sound sources are moving
point sources. A continuous stream of such moving point sources can be
idealized as a line source. Sound energy from a line source is attenuated over
a cylindrical wave front and is attenuated inversely with distance. Thus, noise
from real traffic sources will be attenuated by a factor between 1/d and 1/d2,
where d is the distance from the source. Hence, for road noise sources, it is
reasonable to assume that a doubling of the distance from source to receiver
will result in a drop of at most 6 dB in the sound level. Geometrical spreading
is one of the mechanisms by which highway noise barriers attenuate sound, by
making it travel farther so that its intensity and perceived loudness drop.
Sound Noise
pressure level
(Pa)* (dBA)
120
Concorde
10 707
110
20 Recording studio
10-4
10
10
2d
Insertion loss can be estimated by using the model proposed by Kurze and
Anderson (Kurze 1971). It is the result of compiling data of many researchers
onto a single plot and developing a curve fit for a point source. The equation
is below and the plot is shown in Figure 2.4.
⎛ 2πN ⎞
IL = 5dB + 20 log ⎜⎜ ⎟ dB
⎟ up to N = 12.5
⎝ tanh 2πN ⎠ (2.1)
IL = 20 dB for N > 12.5
( a + b − l) f
N= (2.2)
co
l is the original length of the direct path from source to receiver
a and b are the lengths of the two straight-line segments comprising the path
as modified by the noise barrier
f is the sound frequency in Hz
co is the speed of sound propagation in air (approximately 1100 ft/sec)
The illustration below is used in an example calculation. The noise wall is
12 ft from the nearest tire, and is 12 ft tall. A house is 15 ft beyond the barrier
and has a window at a height of 4 ft.
11
The length of the original direct path is :
l = 27 2 + 4 2 = 27.3 feet
Hence :
a + b − l = 34 − 27.3 = 6.7 feet
at f = 100 Hz, the Fresnel number is
6.7 * 100
N= = 0.61
1100
The calculated insertion loss can be compared with the predicted value in the
graph below (referred to as Eqn 19). The calculated insertion loss is close to
the measured value from experimental data.
b
a
12
l
12 15
12
40
Rathe’s data
30
Eqn. (19)
∆L,dB 20
10
0
0.10 0.25 1.00 2.50 10.0 25.0
N
Figure2.4 Insertion loss versus Fresnel number for experimental and empirical data
Field measurements can provide very accurate sound data for the time
monitored. However, unless measurements are repeated many times at each
site, it is difficult to determine whether the recorded noise levels are
representative. This is because environmental conditions such as wind and
temperature gradients can significantly alter sound levels. Recorded noise
levels also can be influenced by typical urban noises that are not traffic-
related, such as aircraft flyovers, fire sirens, construction activities or even
animal or insect noises. It is possible to avoid these nontraffic-related noises,
but the duration of monitoring must be substantially increased and some
recorded data may be invalidated.
In summary, field measurements are very costly and labor-intensive.
Computer models can overcome these disadvantages. Several such models
have been developed for predicting the effectiveness of highway noise
barriers. Typical of these computer models are STAMINA 2.0, OPTIMA and
Traffic Noise Model (TNM). STAMINA 2.0 and OPTIMA have largely been
replaced by TNM. In this chapter, these models are briefly discussed. Their
basic principles are reviewed, their most common applications are discussed,
and their capabilities and limitations are noted.
13
STAMINA 2.0 and OPTIMA
STAMINA 2.0 was formerly the most commonly used model for predicting
highway noise attenuation by a barrier. It was developed for the Federal
Highway Administration (FHWA) by the acoustical consulting firm of Bolt,
Beranek and Newman. It is designed to model up to 30 roadways, 20 barriers,
and 40 receivers in a single run. It creates a data file for use by another
program, called OPTIMA, which determines the most effective barrier heights
and lengths for the specified geometry. As many as 8 barrier heights can be
modeled in each OPTIMA run.
STAMINA is the traffic noise prediction program most commonly used by
state highway agencies, including the Texas Department of Transportation
(TxDOT). Many states, including Texas, have developed input modules to
make STAMINA easier to use. In fact, so many input modules have been
developed and widely distributed that even the FHWA does not possess any
original versions of the program.
The major limitation of the STAMINA program stems from the limitations of
computer hardware that prevailed at the time of its development. STAMINA
was initially developed for use on mainframe computers, because those were
the only ones available with the necessary computational power. Because
mainframe computer time was expensive, STAMINA was written to use only
a single frequency of 500 Hz for analysis of noise, rather than a 1/3-octave
band analysis.
Highway traffic produces a range of noise within the human hearing spectrum
from 100 to 4,000 Hz. Trucks produce a different noise-frequency spectrum
than do passengers cars. As reported earlier, the attenuation of sound and the
perceived annoyance of sound are frequency-dependent. The choice (for
STAMINA) of the single 500-Hz frequency is a good compromise between
the most dominant traffic noise frequencies, and the more-annoying, slower-
attenuating, lower-frequency noise. However, a single-frequency analysis has
limitations in analyzing specific situations.
Traffic volumes in STAMINA 2.0 are based on Design Hourly Volume
(DHV). Usually, Level of Service C traffic volumes and associated running
speeds are used to predict the worst-case scenario. From this information,
STAMINA 2.0 calculates the equivalent sound pressure level, Leq (the
constant sound level that would deliver the same sound energy as the given
time-varying signal).
The current version of STAMINA 2.0 is a single-screen model that is
independent of ground impedance. It uses an incoherent line-barrier algorithm
based on the work of Kurze and Anderson (Kurze 1971), and a single wall
design curve for point sources from Maekawa’s (1968) work. Noise
attenuation is first calculated for a point source, and then expanded to a line
source via integration over the barrier length.
Three types of barriers can be modeled in STAMINA 2.0: absorptive,
reflective, and structural. Other factors used by the model are “alpha factors”
14
and “shielding factors.” Alpha factors describe the effect of hard or soft
ground on noise propagation from the source to the receiver. Shielding factors
account for additional noise attenuation attributable to buildings, trees, or
terrain features. The default alpha factor of STAMINA 2.0 corresponds to
“hard ground.” When an earth berm is used, the predicted attenuation is
increased by 3 dB because of these soft-ground propagation effects.
When estimating the noise attenuation by a barrier, STAMINA 2.0 uses
source heights of 0 m, 0.7 m, and 2.4 m for automobiles, medium trucks, and
heavy trucks, respectively.
An evaluation by Hatano indicated that STAMINA 2.0 tends to overpredict
before-barrier noise levels by an average of 2.9 dBA and after-barrier noise
levels by 3.8 dBA (Hendricks 1987).
The following rules of thumb are often used to check results of computer
simulations:
1. If the traffic volume is doubled and the roadway geometry does not
change, the noise level will increase by 3 dB. If the traffic volume is
increased 10 times, the noise level will increase by 10 dB.
2. If average vehicle speed increases by 8 kph (5 mph), and the percentages
of cars, medium trucks, and heavy trucks do not change, the noise level
will increase by 1 dB.
3. If one traffic lane is added, the noise level will increase by 1 dB.
4. If the distance from the roadway to the receiver is doubled, the noise level
will decrease by 4.5 dB for soft ground and 3 dB for hard ground.
Conversely, halving the distance will increase the noise level by 3 or 4.5
dB depending on the ground hardness.
15
program RAYVERB, which is computationally consistent with the model of
TNM. The following explanation is relevant to RAYVERB as well as TNM.
Input to TNM
Within Windows, TNM allows digitized input using a generic Windows
digitizer driver, plus the import of DXF files from CAD programs and input
files from Stamina 2.0. To aid during input, TNM shows and plots the
following graphical views:
• plans;
• skew sections;
• perspectives; and
• roadway profiles, which help during input of roadway Z coordinates.
These input graphics are dynamically linked to input spreadsheets, where
noncoordinate input may be entered, and digitized input may be modified.
16
TNM combines these noise emissions with its internal speed computations to
account for the full effect (noise emissions plus speed) of roadway grades and
traffic-control devices.
TNM also allows user-defined vehicles. For each, the user enters three
measured parameters for A-level emissions as a function of speed (cruise
throttle, average pavement).
To document input, TNM plots its input graphics and the following input
tables:
• roadways;
• traffic for TNM vehicles;
• traffic for user-defined vehicles;
• receivers;
• barriers;
• building rows;
• terrain lines;
• ground zones;
• tree zones;
• noise contour zones;
• receiver adjustment factors;
• structure barriers; and
• barriers with important reflections.
Calculation and Sound Propagation in TNM
TNM calculates the propagation of sound energy, in 1/3-octave bands
between roadways and receivers. Calculation of sound propagation takes the
following factors into account:
• divergence;
• atmospheric absorption;
• intervening ground (acoustical characteristics and topography);
• intervening barriers (walls, berms, and combinations or sequences
thereof) intervening areas of dense trees and undergrowth.
TNM computes the effect of intervening ground (defined by its type, or
optionally, by its flow resistivity) using acoustical theory calibrated against
field measurements. In addition, TNM allows sound to propagate underneath
selected intervening roadways and barriers, rather than being blocked by
them. TNM also computes single reflections from vertical wall barriers, with
user-selected Noise Reduction Coefficients.
17
check, to determine if noise barriers break the lines of sight between sources
and receivers.
18
Absorptive Materials and Highway Noise Barriers
19
noise, was tested for freeze-thaw resistance. Repeated freeze-thaw cycles
resulted in a substantial loss of mass and deterioration of the surface, making
porous concrete unsuitable for use in absorptive barriers in environments
where they would have to endure freeze-thaw cycles (Lane 1989). In addition,
absorptive barriers can be very expensive to manufacture (Menge 1978).
Highway noise barriers are made of many different materials. In this section,
those materials are reviewed with particular emphasis on the specifications
commonly used to identify them and prescribe their quality. Previous work by
the University of Louisville (HITEC 1996) proposes the evaluation criteria
summarized here. Those criteria are not intended to be all-inclusive. The
information given below is proposed as a basis for TxDOT and its own
materials-evaluation personnel’s use in developing appropriate criteria.
In addition to meeting materials standards, noise barriers of each material
must meet the requirements of the appropriate structural design code. Those
requirements are discussed in Chapter 3 of this report.
Aluminum
Aluminum is useful for highway noise barriers because of its generally low
maintenance requirements. It is also light in weight. Section 1.3.3 of this guide
prescribes minimum thicknesses for acceptable acoustical performance.
Aluminum’s value in the recycling market has given TxDOT problems with
thefts of aluminum components such as guardrails. This possibility should
also be considered for aluminum noise-barrier components.
In specifying aluminum highway barriers, the University of Louisville
recommends that panels made of aluminum have a minimum nominal
thickness of 0.063 inch and conform to the thickness tolerances of the
Aluminum Association. Also, any shearing, cutting, or punching of the panels
should preferably be done before any coatings are applied to them.
20
Section 6.3.2.1 of Canadian Standards for Noise Barrier on Roadways, which
is a modified version of ASTM C672 (“Standard Test Method for Scaling
Resistance of Concrete Surfaces Exposed to Deicing Chemicals”).
In that modified standard, a specimen’s loss of mass is determined after
exposure to a prescribed number of freeze-thaw cycles involving distilled
water, ordinary water, or even deicing solution. The acceptance criterion is
based on the effects of freeze-thaw deterioration or salt scaling, or both, on the
concrete’s acoustical and structural performance and on the severity of
exposure anticipated in service. In general, test specimens should not exhibit
any cracking, spalling, or aggregate disintegration after exposure to the
required number of cycles. When severe exposure is anticipated, acceptance
criteria could also include a maximum permissible loss of mass after cycling.
To date, no single, definitive, cost-effective and widely accepted method is
available for evaluating noise barriers for resistance to salt scaling. The
University of Louisville (HITEC 1995) recommends the modified ASTM
C672 as a good starting point, but notes the possible need for future
modifications. For example, the number of freeze-thaw cycles between tests
might be increased in the later stages of the evaluation, to reduce testing costs
without increasing the risk of unacceptable materials.
Masonry
Masonry is widely used for highway noise barriers because of its durability
and aesthetic appeal. Masonry units can be laid in place or used in
prefabricated panels that are later placed between post or column elements.
Masonry comprises units, mortar, grout, and accessory materials. Units must
be of concrete or fired clay masonry. Concrete masonry units should be
hollow load-bearing units conforming to ASTM C90. Fired clay units (solid or
hollow) should conform to ASTM C62, C216, or C652. Masonry mortar
should conform to ASTM C270, and masonry grout, to ASTM C476.
Reinforcement can be either deformed bars or wire joint reinforcement. It and
other accessories should conform to the specifications of the Masonry
Standards Joint Committee (MSJC 2002a, 2002b). A panel cap or flashing
should be used to protect the top course and posts of masonry walls.
Plastics
Plastics are sometimes used for highway noise barriers. Their attractive
features include light weight. As noted earlier, a minimum weight is necessary
for acoustical effectiveness. The principal potential drawbacks of plastics are
deterioration under exposure to ultraviolet radiation and ozone.
Panels made of plastic or fiberglass should be tested for resistance to
ultraviolet-light exposure in accordance with ASTM G53. The specimen is
alternately exposed to ultraviolet light alone from a series of fluorescent lamps
and to condensation alone in a repetitive cycle. There must be no
delamination, fading, chalking, or embrittlement after 1,500 hours of
21
exposure. All glazing material must comply with the requirements of ANSI
Standard Z 26.1.
Steel
Steel is attractive for use in highway noise barriers because of its low cost. Its
chief potential drawback is its vulnerability to corrosion. This vulnerability is
most often counteracted by galvanizing and coating the steel.
According to the University of Louisville, all steel panels should be at least
20-gauge galvanized steel, and should also be protected with a coating with
satisfactory tested resistance to weathering, fog-spray exposure, and flame
spread. Whenever possible, the coating should be applied only after the steel
is sheared, punched, or cut. Panels should be connected using aluminum pop
rivets with an aluminum or stainless steel mandrel.
Wood
Wood is used for noise barriers in areas with abundant supplies of this
material. Its principal potential drawbacks include its relatively low mass, in
that a significant thickness is needed to achieve a satisfactory transmission
loss. Drawbacks also include the need to avoid gaps between pieces of wood,
and possibly higher maintenance costs to control decay.
Resistance to rot and decay is the most important maintenance consideration.
According to the University of Louisville, any wood products used in noise
barriers should either be naturally resistant to decay for a minimum period of
20 years, or be pressure-treated. All pressure-treated wood should have a
Certificate of Preservative Treatment from an appropriate facility. Minimum
retention should be 0.6 pound per cubic foot. The moisture content of all
sheathing should be reduced to a maximum of 15 percent before and after
pressure treating. Timber columns should be reduced to an exterior moisture
of 15 percent to the depth of the penetration of the preservative and an interior
moisture content of 30 percent maximum. All wood products should be
treated to resist insect infestation, and be coated with a wood sealer or stain.
Laminated wood panels must resist warping, splitting, or loosening of
particles, knots, and imperfections. Any sheathing must be double-depth,
tongue-and-groove.
Glue-laminated wood containing a wet-use adhesive should conform to
ANSI/AITC A 190.1. Any preservative treatment should be in accordance
with AWPA C-28. Any wood to be glue-laminated should be preservative-
treated under pressure, to a retention of 0.4 pound per cubic foot, prior to
gluing. All glues should be water-resistant in accordance with CSA Standard
01 12-M. Nonlaminated wood should be No. 2 grade or better. Any plywood
used should be an exterior type conforming to the requirements of U.S.
Product Standards PS-1. Comparable ASTM standards are acceptable
substitutes for the Canadian standards mentioned above.
22
Evaluation of Proprietary Barrier Materials
24
Multiple-Reflection Issues
• Multiple reflections of traffic noise between two parallel plane surfaces,
such as noise barriers or retaining walls on both sides of a highway, can
theoretically reduce the effectiveness of individual barriers and contribute
to overall noise levels. Associated increases in traffic noise levels will
normally not be perceptible to the human ear, however, if the distance
between the barriers is at least 10 times the average height of the barriers.
For example, two parallel barriers 3 meters high should be constructed at
least 30 meters apart. During the preliminary design of noise barriers, the
possible influence of parallel reflections should be checked.
25
26
CHAPTER 3
STRUCTURAL DESIGN OF NOISE BARRIERS
Introduction
Definitions
The distinction between the meaning of the terms “right-of-way” and “clear
zone” is often unclear or misunderstood. In this report, these terms are defined
as follows (Civil Engineering Handbook 1995):
The right-of-way is the land area (width) acquired for the provision of a
highway.
The clear zone is the unobstructed, relatively flat area outside the edge of the
traveled way, including shoulder and sideslope, for the recovery of errant
vehicles. Clear zone is defined in the TxDOT Highway Design Division
Operations and Procedures Manual.
P = 0.00256 (1.3V)2 Cd Cc
where P is the wind pressure, V is the design wind speed based upon 50-year
mean recurrence interval; Cd is the drag coefficient (taken as 1.2 for sound
walls); and Cc is the combined height, exposure, and location coefficient. The
wind speed is increased by a factor of 1.3 to account for the effects of gusts.
As evident from this equation, the design wind pressure depends on the height
of the sound wall and the setting in which it is placed. For instance, a sound
wall located in the city is expected to experience lower wind loads than an
otherwise identical sound wall located in the country. These factors are
27
incorporated in the coefficient, Cc. A detailed procedure for applying design
wind loads to sound walls is available in AASHTO (1992).
In design, the forces and moments resulting from wind loads on a sound wall
must be checked against the sound wall’s lateral load capacity. However,
applicable codes and guidelines do not address sound-wall deflections, nor do
they specify deflection limits for sound walls. For most sound walls,
deflections under design wind loads are neither a strength or a stability
concern, nor are they the subject of public attention. When taller sound walls
are constructed, however, deflections may be perceived by the public as a
potential safety hazard. This is especially pertinent when the design uses
unbonded tendons placed at the centroid of vertical posts. This design
typically has a small internal lever arm and a long length of unbonded tendon,
leading to large lateral deflections.
28
In considering this issue, it is important to reiterate current TxDOT policy.
All highway noise barriers located within the clear zone must be protected by
a separate traffic barrier. If the noise barrier is integrated with the traffic
barrier, it is required to resist vehicular impact. To meet FHWA guidelines, all
such barriers must be crash-tested. In practical terms, the most effective way
to meet these requirements is to put a crash-tested vehicle impact barrier in
front of the noise barrier. Then the noise barrier itself would not have to be
designed for vehicular impact.
29
Structural Design Requirements Imposed by Adjacent Utilities
31
32
CHAPTER 4
SAFETY CONSIDERATIONS IN THE DESIGN OF NOISE BARRIERS
Introduction
33
Requirements Related to Vehicular Impact
34
CHAPTER 5
AESTHETIC CONSIDERATIONS IN NOISE BARRIER DESIGN
2. design the wall to perform the function of noise reduction while blending
it into the surrounding environment; or
3. design the wall as an art form (line, form, color, texture, and artistic
expressions) within the context of its surroundings.
The TTI survey of states also noted that a previous 1981 study indicated that
only Pennsylvania and Minnesota reported aesthetic treatment of noise
barriers. In the TTI survey, states reported including aesthetic criteria into
several noise-abatement projects because of public involvement.
Aesthetic standards for noise wall design are more codified in Europe than in
the U.S. In 1991, the Danish Ministry of Transport published Report 81, Noise
Barriers⎯A Catalogue of Ideas (Denmark 1991). This report contains a
comprehensive photographic database of the different types of noise barriers
constructed in Denmark and other neighboring countries. In addition, it
discusses in qualitative terms the factors and methodology used in planning
and designing a noise wall.
35
1995 Organization for Economic Cooperational
Development⎯Roadside Noise Abatement
In 1995, the Organization for Economic Cooperational Development (OECD)
published an excellent report on roadside noise abatement that synthesizes the
experiences of Europe, Japan, Australia, and the United States. In regard to
aesthetic considerations, the report discusses visual effects of both sides of
noise barriers, effects on drivers, barrier termination, and graffiti. The report
concludes that aesthetic design and the integration of noise barriers into the
landscape and the environment are of special importance. It also states that
barrier height, the choice of material, and the shape, structure, and color of the
barrier are especially important considerations. The report concludes that the
successful design approach for noise barriers should be multidisciplinary and
should include architects, planners, landscape architects, roadway engineers,
acoustical engineers, and structural engineers.
The visual effect of the noise barrier on the driver depends on the speed of the
vehicle, the height of the barrier, the distance of the barrier from the roadway,
and the surface texture of the barrier. If vehicles are generally moving rapidly,
close to the barrier, drivers do not notice the details of the barrier. If the
vehicles move more slowly, or if the barrier is farther away, the details of the
barrier are noticeable and therefore more important. If the barrier is high and
close to the driver, and particularly if it is on both sides of the roadway, it may
produce, a tunnel effect in which drivers perceive themselves as being
uncomfortably surrounded by the barrier.
The visual effect of the noise barrier on the receiver depends on the barrier
height, the distance of the barrier from the receiver, and the surface texture
and color of the side of the barrier facing the receiver. This visual effect can
be accentuated if the barrier changes the pattern of light and shadow on the
receptor’s property. The surface texture of a noise barrier depends on the type
of material used to construct the barrier. For example, wood-textured concrete
can have horizontal or vertical planks. The aesthetic advantage of using
36
horizontal planks is that the seams in stacked panels are less noticeable. Solid
panels, however, may be aesthetically preferred for wall heights under 14 feet.
Two design approaches are available to mitigate any undesirable visual effect
that noise barriers may have. In the first approach, the barrier is designed to be
monumental, dominating the landscape. Its materials and details are selected
so that it becomes a pleasing part of the landscape. In the second approach, the
barrier is designed to blend with the landscape. This approach is best
exemplified by the selection of a noise barrier in the form of an earth berm.
While right-of-way constraints can make an earth berm impractical, other
options are also available. Whichever approach is taken, it is advantageous
that the visual appearance of the noise barrier reflect the historical and
architectural context of the region in which it is placed. For example, noise
barriers in a coastal area can be colored to blend with the sand that surrounds
them; or, they can be decorated or patterned with symbols that are historically
meaningful for the area.
Role of Opacity
Another aesthetic issue related to noise barriers concerns their opacity. Most
barriers in the United States are of opaque materials such as concrete,
masonry, or wood. Opaque barriers can block the view of motorists and make
driving monotonous. One way to overcome this problem and at the same time
achieve a better aesthetic result is to use transparent materials for barriers. A
variety of transparent materials has been promoted for use in highway noise
barriers. The most common are thermosetting acrylic polymers, known by
such trade names as Plexiglas, Butacite, Surlyn, and Lexan.
37
The primary advantage of transparent materials over opaque ones in noise
barriers is aesthetics. Many transparent plastics become brittle or discolored in
the presence of ultraviolet radiation and ozone, however. Because their
transparency is degraded by highway dirt, they may require periodic cleaning.
In addition, the perceived aesthetic advantage of transparent barriers for
motorists are often countered by the perceived aesthetic disadvantage for
residents, who may not want an unobstructed view of nearby traffic. Formal
and informal research studies indicate a connection between how opaque
noise barriers block the view of traffic and how they are perceived to block
noise. For example, although a wooden privacy fence may be measurably
ineffective as a noise barrier, it is nevertheless usually perceived by residents
as effective, because it blocks their view of traffic. Conversely, transparent
noise barriers may be perceived as acoustically less effective by residents,
because of their transparency.
General Guidelines
The general guidelines for design of noise barriers with respect to aesthetic
treatment are:
38
CHAPTER 6
TEXAS EXPERIENCE IN NOISE-BARRIER CONSTRUCTION
about 20 feet
Sub-Module
Sub-Module
Sub-Module
Elevation View
39
Figure 6.2 Example of prefabricated, separate post-and-panel system (Houston District)
In this system, there is no grade beam. The panels span between the posts,
whose spacing is often dictated by the type and layout of the foundation used.
The post spacing typically ranges from 3.0 to 7.5 m (10 to 25 feet). Drilled
shafts without grade beams are the standard foundation type for all noise
barriers in the Houston District. The precast panels are typically reinforced
concrete and are “flown” into place between the columns, using an overhead
crane.
40
the presence of overhead utilities or restrictions on crane operation so
dictate, the required lifting height or panel weight can be reduced by using
multiple, partial-height panels, rather than a single large panel. The panels
can have a wide variety of surface textures and colors.
Figure 6.4 Example of prefabricated, separate noise barrier system (Houston District)
41
Plan View
about 20 feet
Sub-Module
Sub-Module
Sub-Module
Elevation View
42
Serpentine Walls
A serpentine-wall system is popularly known as the fan-wall system, and will
be referred to as such throughout the rest of this guide. It is generally
composed of full-height, precast panels placed in a zigzag configuration in
plan and interconnected using bolts or cables. This zigzag configuration
provides stability against overturning, permitting the elimination of posts. In
certain areas with very good soil conditions, the foundation can consist only
of a compacted base. This system has the potential advantage of low cost
because of the elimination of posts and foundation. However, its zigzag
footprint requires more ROW than a straight wall. A fan-wall system can be
constructed with less concern for disturbing buried utilities. It can make
subsequent access to such utilities more difficult, however, because its
overturning stability can be endangered if it is necessary to dig along a
significant length of the wall. The fan-wall system construction in the Austin
District and shown in Figure 6.7 was specifically chosen because of the
presence of buried utilities.
The Houston District has constructed examples of the fan-wall system (Figure
6.8). The fan-wall system used in Houston differs in footprint from that of the
one used in Austin. The Houston system is wider, requiring more ROW. Even
though this wall has no drilled-shaft foundations, the Houston District now
requires drilled shafts under all future walls because of the possibility of
overturning as a result of trench excavation. The Houston District has noted
that the irregular shape of the fan wall makes it difficult to mow next to the
wall.
43
Figure 6.8 Example of fan-wall system (Houston District)
Staggered Walls
The staggered-wall system alternates straight and angled wall sections while
incorporating the use of stackable, post-and-panel construction. The staggered
barrier is interrupted at regular intervals with a short section perpendicular to
the roadway. As shown in Figure 6.9, a staggered wall is less monotonous
than a straight one. Its footprint provides some inherent lateral stability. This
footprint is usually used with the prefabricated post-and-panel system, but it
could be used with other systems as well.
Earth Berm
An earth berm is simply a mound of dirt. In some instances, the center of the
berm is filled with alternate materials (such as recycled tires) to reduce costs.
Earth berms have the aesthetic advantages of being less imposing and more
natural in appearance than noise barriers of other materials. Vegetation on the
berm can enhance this aesthetic appeal. However, trees planted on an earth
44
berm noise barrier can reduce the barrier’s acoustical effectiveness by
scattering noise to the receivers that otherwise would have been directed over
them. Earth berms can be topped with other types of noise barriers to increase
their acoustical effectiveness. The main disadvantage of earth berm noise
barriers is the ROW they require. Earth berms are a practical solution if space
is available. The Fort Worth District has one such barrier.
The posts are typically attached to the impact barrier using a base plate and
embedded anchor bolts. This connection is often difficult and costly to
construct in the field because of the tight tolerances resulting from the narrow
barrier top (only 150 mm [6 inches] wide). Because the barrier top is so
narrow, the base plate is also narrow, and the overturning resistance of the
post is low. As a result, the post spacing must be close⎯Fort Worth used a
spacing of only 1.5 m (5 feet). The panels must therefore be short. While more
panels are required than if the posts were farther apart, the smaller panels are
stacked and are easier to disassemble if necessary. The short panel length and
exposed steel posts have resulted in a poor aesthetic rating for this design.
Wind loads also restrict the height of this barrier system. The concept was
45
designed for ease of disassembly should ROW ownership change, but so far
this feature has never been put to use.
46
Figure 6.11 Example of sloped-face noise barrier system (Houston District)
47
48
CHAPTER 7
SAMPLE SPECIFICATIONS AND PLANS
Introduction
The sample specifications are applicable to most commonly used sound wall
materials and systems and can address many, if not all, proprietary systems.
The sample drawings are also applicable to a variety of systems and materials.
The sample specifications and drawings should be adapted to the particular
needs of each project.
49
Sample Specifications
ITEM 5246
SOUND WALLS
50
♦ ITEM 449, “ANCHOR BOLTS”
3. GENERAL
51
THE CONTRACTOR SHALL SUBMIT TO THE ENGINEER SEVEN (7) SETS OF
CASTING DRAWINGS FOR PRECAST SEGMENTS AND SHOP DRAWINGS
FOR EACH DETAIL OF THE PLANS REQUIRING THE USE OF STRUCTURAL
STEEL, SEVEN (7) SETS OF CONSTRUCTION DRAWINGS AND TWO (2) SETS
OF DESIGN CALCULATIONS. UPON COMPLETION OF CONSTRUCTION,
ONE (1) SET OF REPRODUCIBLE AS-BUILT DRAWINGS SHALL BE
SUBMITTED TO THE ENGINEER.
52
4. CONSTRUCTION METHODS. CONSTRUCTION OF SOUND WALLS SHALL
CONFORM TO THE DESIGN AND DETAILS SHOWN ON THE PLANS AND TO THE
PERTINENT REQUIREMENTS OF THE FOLLOWING ITEMS:
ALL POSTS SHALL BE SET PLUMB AND FIRM TO THE LINE AND GRADE
SHOWN ON THE PLANS. HORIZONTAL ALIGNMENT TOLERANCE SHALL
NOT EXCEED 3/4 INCH FROM POST TO POST. THE OVERALL VERTICAL
SWTOLERANCE OF THE WALL (PLUMBNESS FROM TOP TO BOTTOM)
53
54
Houston Generic Post and Panel Noise Barrier Sample Drawings
55
Figure 7.2 TxDOT Generic Post-and-Panel Noise Barrier Sample Drawings⎯Houston
District (Sheet 2 of 8)
56
Figure 7.3 TxDOT Generic Post-and-Panel Noise Barrier Sample Drawings⎯Houston
District (Sheet 3 of 8)
57
Figure 7.4 TxDOT Generic Post-and-Panel Noise Barrier Sample Drawings⎯Houston
District (Sheet 4 of 8)
58
Figure 7.5 TxDOT Generic Post-and-Panel Noise Barrier Sample Drawings⎯Houston
District (Sheet 5 of 8)
59
Figure 7.6 TxDOT Generic Post-and-Panel Noise Barrier Sample Drawings⎯Houston
District (Sheet 6 of 8)
60
Figure 7.7 TxDOT Generic Post-and-Panel Noise Barrier Sample Drawings⎯Houston
District (Sheet 7 of 8)
61
Figure 7.8 TxDOT Generic Post-and-Panel Noise Barrier Sample Drawings⎯Houston
District (Sheet 8 of 8)
62
San Antonio−FM3009 Noise Barrier Drawings
Figure 7.9 TxDOT FM 3009 Concrete Masonry Unit Noise Barrier Sample Drawings⎯
San Antonio District (Sheet 1 of 6)
63
Figure 7.10 TxDOT FM 3009 Concrete Masonry Unit Noise Barrier Sample
Drawings⎯San Antonio District (Sheet 2 of 6)
64
Figure 7.11 TxDOT FM 3009 Concrete Masonry Unit Noise Barrier Sample
Drawings⎯San Antonio District (Sheet 3 of 6)
65
Figure 7.12 TxDOT FM 3009 Concrete Masonry Unit Noise Barrier Sample
Drawings⎯San Antonio District (Sheet 4 of 6)
66
Figure 7.13 TxDOT FM 3009 Concrete Masonry Unit Noise Barrier Sample
Drawings⎯San Antonio District (Sheet 5 of 6)
67
Figure 7.14 TxDOT FM 3009 Concrete Masonry Unit Noise Barrier Sample
Drawings⎯San Antonio District (Sheet 6 of 6)
68
CHAPTER 8
SUMMARY OF DESIGN REQUIREMENTS FOR SOUND WALLS
General
Design requirements for sound walls can be classified into the following
general categories:
• Acoustical requirements;
• Environmental requirements;
• Structural requirements.
69
Acoustical Requirements for Receptors Located on the Roadway
If the wall must reduce the perceived noise level for receptors located on the
roadway, additional acoustical requirements are imposed. The wall can be
designed to meet these requirements by reflecting the sound upward, away
from the roadway, or by absorbing the sound so that less of it is reflected back
to the roadway. While wall texturing may have advantages for aesthetics or
graffiti control, it does not affect reflected sound.
Depending on the size and location of the wall, the topography and rainfall
characteristics of the area where it is located, and the design practices of the
70
agency responsible for its construction, a formal flood modeling analysis may
be required.
The probable effect of a sound wall on drainage depends on its plan length
(the greater the length, the greater the effect), and also on its plan location
with respect to known characteristics of water flow.
Wall details such as drainage holes have implications for drainage, and should
be addressed consistently for all sound walls. Holes are typically placed in
sound walls to prevent the walls from acting as dams. Experience in Texas
and other states has indicated that the holes should be about 4 inches high. If
they are narrower than that, cans and other debris cannot pass through them; if
they are wider, children and animals can squeeze through them. Acoustical
considerations indicate that as long as the total area of the drainage holes is
less than about 3% of the area of the panel, their acoustical effects are
negligible. Similar comments also apply to the small gaps that are part of
normal construction tolerances in sound walls.
Sound walls should not decrease the safety of those using the roadway, nor the
safety of those adjacent to the roadway.
In some climates, shadow zones created by sound walls can create areas in
which ice can form. Because of the light/dark visual adjustment problems
noted above, the ice can be difficult for drivers to detect, thereby increasing its
potential hazard.
Finally, sunlight reflecting from sound walls, or from layers of water or ice on
the walls, can further impair drivers’ vision.
71
Requirements for Vehicular Impact
Sound walls are not intended to function as vehicular impact barriers. If they
are located close enough to the roadway to be impacted by vehicles, however,
they must either be placed behind a conventional vehicular barrier, or be
mounted on a vehicular barrier. The latter solution is not recommended by
TxDOT. Noise barriers associated with vehicular barriers must be crash-
tested according to FHWA guidelines.
72
Structural Requirements for Sound Walls
Constructability
An efficient structural design, by itself, is not as useful as a less efficient
system that can be easily built.
73
Requirements Imposed by Adjacent Utilities
74
Serviceability Requirements for Sound Walls
75
76
CHAPTER 9
SUMMARY, CONCLUSIONS AND RECOMMENDATIONS
Summary
In this report, the current TxDOT design process for highway noise barriers is
reviewed (Chapter 1). Design requirements for them are then presented.
These include acoustical requirements (Chapter 2), structural requirements
(Chapter 3), safety requirements (Chapter 4), and aesthetic requirements
(Chapter 5). In Chapter 6, examples are given of different highway noise
barriers used in Texas. In Chapter 7, sample plans and specifications are
presented. In Chapter 8, design requirements are broadly grouped into
acoustical requirements, environmental requirements, traffic safety
requirements, and structural requirements; those requirements are again
presented in synthesized form, drawing on the material presented in the
preceding chapters.
77
78
REFERENCES
1471-2 (1996) Peron, Ronald A., “Structural Design of Sound Walls with
Emphasis on Vehicular Impact,” Thesis for The University of Texas
at Austin, May 1996.
Billera (1996) Billera, Domenick, Parsons, Richard D., and Hetrick, Sharon A.,
“Good Fences Make Good Neighbors.”
Blum (1976) Blum, Randolph F., “A Guide to Visual Quality in Noise Barrier
Design,” Implementation Package 77-12, U.S. Department of
Transportation, Federal Highway Administration (FHWA),
December 1976.
Bowlby (1986) Bowlby, W. and Cohn, L. “A Model for Insertion Loss Degradation
for Parallel Highway Noise Barriers,” Journal of the Acoustical
Society of America 80 (1986): 855-868.
79
FHWA (1996a) “FHWA Traffic Noise Model Version 1.0,” The Wall Journal 22
(1996): 14-17.
FHWA (1996b) Hatton, J. H., “Bridge Railing Design and Testing: A Discussion
with the AASHTO Highway Subcommittee on Bridges and
Structures, Technical Committee (T-7) for Guardrail and Bridge
Railing Design,” May 14, 1996.
Menge (1978) Menge, C. W. “Sloped Barriers for Highway Noise Control,” Inter-
noise 78 (May 1978): 509-512.
NCHRP (1993) Ross, H. E. Jr., Sicking, D. L., and Zimmer, R. A., “Report 350:
Recommended Procedures for the Safety Performance Evaluation
of Highway Features,” National Cooperative Highway Research
Program (NCHRP), National Academy Press, Washington, D.C.
TTI (1995) Godfrey, Sally H. and Storey, Beverly B., “Highway Noise
Abatement Measures: 1994 Survey of Practice,” Research Report
80
1994-4, Texas Transportation Institute (TTI), Texas A&M
University System, 1995.
TxDOT (1994) “Specification Drawings for Type T501 Traffic Rail,” Record
Number B589, TxDOT, unpublished.
Wall Journal (1996) Hendricks, Rudy, “To Absorb or not to Absorb,” The Wall Journal
2l (1996): 8-10.
81