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A seemingly endless din assails people from every
quarter: Noise irom the kitchen mixer, radio and
television, cars and trucks, planes and trains, office
equipment and industrial machines, noise layered
upon noise, annoying and sometimes harmful.
To varying degrees, noise affects both the
physical and mental well-being of humans. The most
well known and probably the most serious effect of
noise is loss of hearing. There is also evidence to
suggest that it increases the. level of artery-clogging
cholesterol and raises the blood pressure. Noise has
the opposite effect on the blood vessels of the brain.
It makes them dilate, or enlarge, and this could be
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how noise causes headaches. Noise puts a stress
on the body. Scientists think that it may even change
the secretion of acid by the stomach change the
secretion of endocrine hormones, aflect the func-
tioning of the kidneys and increase susceptibility to
viral infection. And noise affects nerves and
emotions as well
Noise intrucies on periods of rest and relaxation.
The teenager across the street "lays a little rubber"
as he leaves the neighborhood in his hot rod, the
motorcyclist down the block "revs" his bike intermin-
ably prior to departures—shattering your neighbor-
hood's quiet. Even in recreational areas your
solitude is broken by people who have brought their
favorite noise-makers along. Acid-rock music
pierces the air from a new arrival's transistor radio,
an outboard motor boat roars by. Even heavy snow
cannot muffle noise, for there are some 2.5 million
snowmobiles to shatter the quiet.
We know what noise does to people, and conser-
vationists are beginning to wonder about what noise
may be doing to wildlife as well. Because of the
basic quiet in wilderness and recreational areas,
(technically known as low ambient background
levels) irregular noises from vehicles and equipment
are the most disturbing.
This pamphlet focuses on different types of
recreational vehicles, such as motorcycles, power
boats, snowmobiles, ail terrain vehicles (ATV), dune
buggies, and mini-bikes and race cars and the noise
problems associated with them. There has been a
remarkable growth in the number of these vehicles
in the last 20 years and it is a reflection of our times
that with new recreation has come a new environ-
mental problem in the form of noise in those very
locations where people seek quiet.
Throughout this report, we use the word "decibel"
(abbreviated "dB") which is the commonly used
measure of sound. "A ' (as in dB (A)) represents that
scale of measurement which is related to the human
ear's acoustical properties, which have to do with
hearing or with sound as it is heard.
We hope this report will make you more knowl-
edgeable about the problems of noise in recreational
vehicles, particularly if you operate them.

The snowmobile is a relative newcomer on the
leisure vehicle scene. Since its introduction in 1958
as a low-powered, lightweight, go-anywhere-in-the-
snow vehicle, the snowmobile has been redesigned
for family-type use. There are currently about 2.5
million snowmobiles in operation and most are used
for recreation. People who live on farms own about
28 percent of all snowmobiles, and many farmers
and ranchers in the West and Midwest rely on them
for feeding and rescuing storm-stranded cattle. In
addition, foresters and utility workers can use these
vehicles to reach remote areas. The average
snowmobile operator rides about 13 hours a week
during the winter.
The original snowmobile concept called for an
engine light in weight, but powerful for its size. For
this reason, early models possessed unshrouded
engines and unmuffled or poorly muffled exhausts.
The rise in popularity of snowmobiles led to
numerous complaints about their excessive noise.
As more vehicles were produced, users demanded
more and more power until today, some snowmo-
biles are capable of speeds of nearly 100 miles per
hour. Their adverse effect on the environment may
be heightened by the tact that a limited number of
owners remove factory-installed muffler systems in
an attempt to achieve more power. In many cases
this actually results in /ess power and greater noise.
Studies show that continued use of snowmobiles
over a span of many years may cause some
permanent hearing loss to operators and pas-
sengers. Conservationists are also concerned that
noise from snowmobiles may be detrimental to
wildlife, especially in winter when most species are
particularly weak and vulnerable. As a result,
legislation has been introduced in many States to
restrict snowmobile noise levels. Minnesota intro-
duced the first snowmobile noise regulation in 1970.
restricting" their noise level to 86 dB(A) at fifty feet.
Public concern about snowmobile noise prompted
manufacturers to reduce the noise levels of 1971
models. Most of this noise reduction resulted from
improved exhaust systems that may also prolong
engine life and performance. The post-1971 models
produce noise levels ranging from 77 to 86 dB(A)
under maximum noise conditions measured at 50
feet, and 105 to 111 dB in the driver's seat. The noise
levels from pre-1971 models ranged from 90 to 95
dB at 50 feet, and some racing machines reached
noise levels as high as 105 to 110 dB. The operators
of several machines surveyed experienced noise
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levels as high as 108 dB while operating under
normal conditions. (Remember, continued exposure
to noise in excess of 70 dB can result in increased
risk of hearing loss.)
The following list cites the major sources of noise
in snowmobiles:
Exhaust system - The chief source of snowmobile
noise is the engine exhaust. Designs which minimize
engine space and emphasize lightweight construc-
tion. and consumer demands for maximum power,
have restricted the use of highly effective silencing
Mechanical noise - A major factor in the overall
noise oulput of snowmobiles is engine noise. The
lightweight. 2-cycle. highpower design of snowmo-
bile engines limits the application of quieting
techniques to the internal engine structure. Insulated
engine cowlings (covers) provide the most suitable
and practical means for reducing engine noise.
Air intake - Many snowmobile manufacturers do not
quiet the engine aii intake. Unfortunately, this intake
is usually situated ahead of the operator and
contributes to his noise exposure. Some sacrifice in
engine performance may be required to reduce the
noise of the air intake system. Manufacturers are
now producing air-cleaner units which, will aid in
reducing this problem.

The motorboat has been around longer than any
other of the leisure vehicles. Outboard motor noise
was recognized by industry as an annoyance long
before any legislative bodies acted to control its
effect. In Ihe 1 920s and the 1930's. manufacturers, in
response to public pressure, began experimenting
with underwater exhaust systems to reduce noise.
Their success in the 1940s was one ot the factors
leading to a dramatic growth market for motorboats.
In the mid-1950s, more sophisticated quieting
techniques were incorporated, and the outboard
engine has been continually refined since then.
Today's outboard motor probably represents the
quietest example of a two-stroke engine available.
In a recent survey of inboard and outboard motor
boats, the maximum noise level ranged from 65 to 95
dB(A). Small outboard engines (usually 6 to 10
horsepower) made the least noise. In another series
of tests, levels exceeding 110 dB(A) at 50 feet were
recorded for an inboard powerboat - a type used for 
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Mini-bikes are a particularly annoying residential
noise problem. The bikes are normally sold with
mufflers which reduce their noise levels at 50 feet to
the 75 to 80 dB(A) range. These machines are used
primarily by youngsters not old enough to obtain
drivers' licenses. The problem is aggravated when
the stock muffler is replaced with an expansion
chamber exhaust system which the owner believes
will contribute to the engine's power. The machines
are then capable of noise levels reaching 85 to 90
dB(A) at fifty feet.
Motorcycles have undergone a remarkable
increase in popularity over the past ten years. They
have long been criticized for their excessive noise,
and this noise is partly the result of designs which
incorporate lightweight featuies while sometimes
neglecting adequate mufflers. Many motorcycle
riders associate noise with power and performance
This association is no longer valid with modern
designs, particularly for two-strcke engines. The
major manufacturers have taken steps only recently
to change this belief. Currently, the industry is in the
process of trying to convince the consumer that
more noise does not necessarily mean more power.
This is an essential step in preparing the consumer
to accept the quieter, new-generation of motorcy-
Most current production motorcycles intended for
highway use comply with the California noise
standard. Under the guidance of the Motorcycle
Industry Council most major manufacturers have
agreed to place mufflers on all their off-road
motorcycles to limit their noise levels to 92 dB(A) at
50 feet.
The noise levels of current motorcycle models
vary widely depending on the manufacturer and the
engine size. Most motorcycles now meet the 86
dB(.A) maximum noise specification imposed by
several States. Achieving further noise reductions
will mean some design compromises, but the
technology does exist to produce quieter motorcy-
The amount of noise a motorcycle produces while
cruising depends on its speed and the way it is
operated. Many off-road motorcycles are capable of
speeds of 80 to 100 mph, and are often operated in
the lower gears or at medium to high engine
revolutions. Except when cruising at constant
speeds, these vehicles are operated at full throttle,
and near their maximum noise output.
The exhaust contributes the most to the motorcy-
cle's overall noise level. Although exhaust systems
can be designed to reduce this noise, significant
engine housing and weight limitations must be
A critical problem that remains to be solved in
silencing motorcycles is engine and mechanical
noise. Insulated cowlings have been found to be
impractical solutions for quieting air-cooled engines.
The U.S. Environmental Protection Agency plans to
propose standards for newly manufactured motorcy-
cles in 1977.

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Race Cars
Many people don t realize the amount of noise
generateo by an auto speedway unless they aie
spoits-cai enthusiasts 01 live near an auio tiack To
fans, the noise is pail of the attraction, and fans
equate a race cat's noise with its power An
individual living near a speedway, however, may feel
differently about the noise and traffic and its effect
on the enjoyment of his property Legal action and
civil suits are pending against speedways all over
ihe United States, and in some areas, local
legislation restncting noise levels has forced some
speedways to close
Beltsville Matyland provides an interesting exam-
ple of how citizens were successful in easing a
speedway noise pioblem Aftei receiving numerous
complaints about a local speedway's noise, county
officials conducted a suivey to find the extent of the
problem The survey results snowed that the
speedwav was a serious disturbance in the com-
munity, and thai further study and corrective action
were warranted
Officials believed that barriers could be used to
reduce the racing noise reaching the community
However, barriers made of straw, two bales deep
were found to be inadequate The County Commis-
sioners then issued a peimit which stipulated that
racing would be permitted only after the speedway
owners erected a barrier constructed of half-inch
plywood. 20 feet high and 1.100 feet long The per mil
also stated that no racing would be permitted after
11 p m , and that sound measurement would have to
be continued at the speedway's expense to provide
a basis for considering the next year's permit
New surveys taken in 1971 showed that noise
levels from the speedway were still annoying and
that further action would be required Continued
complaints finally resulted in an ordinance prohibit-
ing racing with vehicles not equipped with exhaust
mufflers, and requiring the speedway to limit us noise
impact on the community to 60 dB(A) This created a
new problem since there was little information about
the noise-reducing capability of race car mufflers
and their effects on engine performance, cooling,
and racing speeds
Alter many tests, a particular brand of muffler was
found that could deliver performance and achieve a
20 dB noise reduction This became standard racing
equipment at the speedway The initial spectator
reaction was not favorable But. after a new speed
recoid was set al the Indianapolis Speedway by a
muffler-equ'pped car. the skeptics were won ovei
The Beltsville experience shows that noise conuol
is workable and practical at most speedways Noise
levels foi all but the nearest neighborhood res'dents
have been loweied to acceptable levels Consistent
and significantly lower noise levels nave been
measured at tiackside With mufflers drivers can
now hear what is going on in their machines and
listen for specific mechanical malfunctions, while
protecting then hearing Fans have found thai ihe
races are as competitive with mufflers as without
them Additionally, the public address system can
now be heard over the noise, and fans actually can
converse during the laces
What you cart do to reduce ihe
roo'bse impact off recreatcos^aS
First of all insist of manufacturers and Stale and
Federal officials that suggestions for ieducing noise
be included with all new power vehicles and
equipment being sold This material should stress
the noise suppression techniques that can be used
by the operator to reduce the noise hazard to himself
and the nuisance factor to others
Wear ear protection devices in the form of
commercially available plugs or muffs Cotton is noi
enough Some snowmobiles motorcycles and boats
present a risk of permanent hearing damage io
operators and passengers
Check your local municipal and State noise
ordinances Some communities have prohibited the
use of powered equipment between the hours of 3
p m and 8am in order to reduce noise annoyance
in local neighborhoods
Finally, compare the noise levels of different
makes of recreational equipment you are planning to
buy This means taking a test ride if possible
Remember, it's your hearing and ihe peace of youi
neighborhood that are involved With increased
buyer preference for quieter machines, manufactur-
ers will respond with more research and develop-
ment in this important area