Environmental Engineering Reference
In-Depth Information
to noisy units demanded quieter units. Anti-noise groups can also force government
agencies to seek out quieter products. From the time the New York City transit trains
began to operate in the 1880s, citizens complained about the noise of these trains.
Citizens became especially vocal about the noise in the late 1970s and learning that
new trains were coming into the system they asked the Authority to bring in trains
with quieter traction motors. At first, the manufacturers claimed that they could not
meet New York's specifications and offered the Authority a noisier traction motor
instead. When New York City pointed out that quieter motors had been delivered
to other transit properties and that these less noisy motors could be adapted to New
York's trains, the manufacturers agreed to exert some effort to provide the quieter
motors, provided New York City paid them to develop the “quieter motors.” These
quieter motors did not cover the first 350 of the 1,100 cars ordered but when they
were installed in the remaining cars, they proved to be quieter and longer lasting
[67]. It should be noted that sometimes quieting products results in products with
longer shelf live to counteract the often heard statement that the problem of noise
mitigation is that it carries a high cost.
Looking at train noise further, we note that one of the major sources of train noise
results from the interaction of steel wheel and steel rails. This interaction sets up
noise producing vibrations in the wheels, rails, track support and ground and within
the train structure itself. Flat wheels and rails that are not continuously welded can
produce vibrations and increased noise. Wheel truing lessens noise but maintaining
the wheel flange contour leads to a longer life for the wheels and rails and places less
stress on the car trucks. Welded rail similarly dampens the noise but this too leads
to less stress on the rail cars. Adding rubber rail seats between the rail and the track
results in a quieter train. It also maintains the integrity of the supporting structure.
Investing dollars in quieting train noise actually saves dollars as we note the benefit
to the integrity of the rail cars, the rails and the structure as a whole. Added to this
is the not insignificant societal benefits that accrue from quieter rail operations.
The noise of train horns at crossings has become a growing environmental prob-
lem for the increasing numbers of people who now live near railroads. The minimum
levels established by the Federal Railroad Administration still encroach upon nearby
residents, leading to many complaints from these people to their public officials. The
introduction of wayside horns, which aim sound directly at oncoming vehicular traf-
fic in both directions perpendicular to the path of the train, would produce a smaller
footprint and be far less intrusive on neighboring communities. The technology to
correct at the problem exists but has not yet been sufficiently utilized in American
communities.
The most important sources of noise arising from motor vehicles are the engines,
transmissions, exhaust systems, and the interaction of tires with the roadway.
Vehicular noise, or rolling noise, results from the interaction of tires with the road-
way. Rolling noise can be reduced by altering the material from which the tire is
made, its speed of rotation and the type of tread. Additionally, rolling noise can be
lessened by improved roadway surfaces and maintaining surfaces which causes less
wear and tear on the automobile itself. The desire to use cleaner, less expensive
fuels has resulted in quieter sanitation trucks [68] and quieter hybrid automobiles
