Environmental Research Needs Background Paper, 1996
Nearly every person in the United States is somehow affected by noise
originating from transportation sources. The primary impact area is
for urban residents affected by noise from major transportation
systems. However, suburban and rural residents are also affected by
noise from interstate and rural highways, aircraft and train sources.
Transportation noise affects people in a variety of ways and people
perceive noise subjectively. An individual located hundreds of feet
from a highway may experience a very low level of transportation
noise, however this noise may be perceived as more annoying than
other, natural noises that may be louder such as birds and insects.
Reflected noise from noise barriers, rock cliffs and other structures
may also be perceived as annoying even though the measured levels of
sound are quite low. Transportation noise may affect the ability of
people to carry on conversations, to concentrate in work and school
settings, and to sleep.
Noise is a major issue associated with the design and construction of
new transportation systems, as well as improvements to existing
transportation systems. Current technologies make it impossible to
design a transportation system that does not produce noise. In
addition, in an era of reduced government funding, the cost of
constructing mitigation measures for environmental impacts is being
strictly scrutinized. This includes noise mitigation measures, which
can be very expensive. Noise barriers can cost in excess of $2
million per mile. In light of these considerations, issues in the
forefront of transportation noise research over the next few years
include: improvements in methodologies used to predict noise levels
from transportation sources; gaining a better understanding of factors
affecting human annoyance of noise; and, analyzing noise mitigation
measures with emphasis on more aesthetically pleasing methods and
alternatives to traditional noise barriers.
The Federal Highway Administration's (FHWA's) Highway Traffic Noise
Prediction Model and, subsequently, its related STAMINA 2.0/OPTIMA
software programs for highway traffic noise prediction and noise
barrier design have been used by analysts for almost two decades.
During this time, improvements have occurred in state-of-the-art
methodology and technology for noise prediction and barrier design.
In addition, the ability to predict transit noise has been imprecise
in the past, with no standard methodology or set of impact criteria
available for transit noise analysis.
Many of the traditional problems with the prediction of noise from
transportation sources have been recently solved, or at least,
substantial progress has been made in rectifying these problems.
Recently, there have been many exciting developments in the field of
transportation noise prediction and control by the key federal
transportation agencies. New noise prediction models have been
developed by the FHWA, the Federal Aviation Administration (FAA) and
the Federal Transit Administration (FTA). The introduction of these
new models has enhanced the ability to accurately predict noise
originating from specific transportation sources.
The FHWA Traffic Noise Model (FHWA TNM) is an entirely new highway
traffic noise prediction model that has a Microsoft Windows interface
and an internal Computer-Aided Design Drawing capability. The FHWA
TNM will calculate traffic noise levels using totally new acoustical
algorithms, as well as newly-measured emission levels for five
standard vehicle types, i.e., automobiles, medium trucks, heavy
trucks, buses, and motorcycles. The calculations will be performed in
one-third octave-bands for each of two subsource heights per vehicle.
The FHWA TNM will output overall a-weighted sound levels for locations
with and without noise barriers. It will allow for analyses of (1)
both constant-flow and interrupted-flow traffic (2) attenuation due to
rows of buildings and dense vegetation, (3) effects of parallel noise
barriers, (4) results of multiple diffractions, and (5) noise
contours. The introduction of this new model promises to improve the
accuracy, as well as the ease of highway traffic noise prediction.
Atmospheric effects on propagation have not been adequately researched
to be incorporated into the highway traffic noise prediction process.
Research should continue to determine the contribution of these
atmospheric effects, with the goal of appropriately including this
factor within TNM.
It has long been recognized that there is a relationship between
roadway pavement type and noise generation characteristics. Research
should be continued to analyze tire and pavement noise
characteristics. Studies should specifically include evaluation of
the effects of age and wear and the long-term stability of various
pavement types.
Construction of noise barriers has been the most often used measure to
abate highway traffic noise. Noise barriers have received mixed
reviews from residents behind the barriers, as well as from drivers
traveling on the highways. Many people find noise barriers
aesthetically unpleasing and find that they lead to a monotonous
driving experience. Research should continue to develop improved
designs for noise barriers which are more effective, economical and
aesthetically pleasing, including the possibility of using alternative
building materials such as recycled materials.
The FAA Integrated Noise Model (INM) has been updated to run under
Microsoft Windows 95. INM Version 5.1 also includes a U.S. Air Force
military aircraft noise database. This model update makes INM more
user friendly. Research is ongoing by the FAA and the airline
industry to reduce the noise generated by aircraft and to design
flight paths that will be efficient and minimize, to the greatest
extent possible, aircraft noise impacts. The major methods for
mitigation of aircraft noise impacts are the purchase of affected
properties or the sound insulation of affected structures. Since the
purchase of impacted residences may not be economically reasonable,
research should continue on improving the use of sound insulation to
mitigate airport noise impacts. A comprehensive study evaluating
various sound insulation treatments in use in the U.S. and in other
countries should be performed, evaluating cost and effectiveness. A
guidance document should be developed to assist in establishing and
managing sound insulation programs.
The FTA has developed a methodology for transit noise prediction and
guidelines for impact determination, found in Transit Noise and
Vibration Impact Assessment (dated April 1995). This document fills a
gap that previously existed in the area of assessment of transit noise
impact. Continued research is needed in this area, specifically the
development of a procedure for estimating sound barrier performance
for railroad noise.
Many areas by transportation noise are affected by noise originating
from more than one source. This is true in many urban areas, where
residents may be affected by a combination of highway, rail and
aircraft noise sources. Research is necessary to integrate noise
prediction methodologies for noise originating from multiple
transportation sources.
Back to Past Meetings Page
Back to main page
file created March 3,
1999 TRB A1F04