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Tue, Feb. 19
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Column: The numbers behind the noise problem

Prescott, as well as other communities, has been noise-impacted, as suggested by the recent meeting with the City Council about motorcycle noise. The current noise ordinance is a subjective one, making it more difficult to define vehicle noise violations. Fortunately, the police department has been authorized to purchase sound level meters, which will permit them to better address this problem. Unfortunately, there is no maximum sound level provision in the existing ordinance. Communities with active enforcement programs have them, and at some point the city should consider adding one to make enforcement more defensible.

The provision must include a number representing the maximum level allowed. Regulations, subsequent to the federal Noise Control Act of 1972, require manufacturers of motorcycles to restrict sound output to 80 dB(A) at 50 feet. The majority of states with noise statutes, including Arizona, have also set the same limit. How reasonable is that number? Some measurements were made on Iron Springs Road with motorcycles at near 45 mph. An unmuffled motorcycle created 93 dB(A) at 50 feet while another made only 65 dB(A). It is clear that motorcycles can meet the above maximum even for speeds over 35 mph.

There has been concern about measurement difficulties because of road grades, sound reflections and measurement distances. Illinois provides a 2 dB tolerance for grades greater than 3 percent. Objects more than 20 feet away have negligible influence. Several states have a table of level corrections for distances other than 50 feet. There really is very little restriction to measuring motor vehicle noise with sound level meters.

Unmuffled motorcycles are one of the major sources of excessive noise. Although federal and state law prohibits modifying mufflers to permit sound levels greater than the new vehicle standard, they are mostly ignored. Sound monitoring, similar to speed monitoring, results in requirements for corrective action.

Boulder, Colo., used the "soft fuzz" approach. A vehicle in violation was given a suspended fine and told to use the fine dollars toward replacing the muffler. If a subsequent violation was found, both the past and current fine was applied. It showed that the effort was to produce community quiet not create income.

A California transportation committee recommended that motorcycles built after 2010 must display EPA labels. Denver is using label monitoring as an enforcement tool. With an adequate education program, these rules are preventive.

The Salt Lake County Health Department has gone one step further in preventing costly modifications to vehicles in violation. They require any dealership, or shop, that modifies or replaces mufflers to have a conspicuous sign indicating that they must meet manufacturer's original specifications.

The city has other noise problems. Many communities have faced the subjective aspect successfully with two ordinance definitions. They define noise disturbance as any sound which: 1) endangers or injures people; 2) annoys or disturbs reasonable people of normal sensitivities; or 3) endangers or injures personal or real property. Section 8-4-1 of the Prescott ordinance is equivalent. They also define plainly audible as any sound for which the information content is unambiguously communicated to the listener, such as, but not limited to, understandable speech, comprehension of whether a voice is raised or normal, repetitive bass sounds, or comprehension of musical rhythms. They add a distance at which it is applied. Section 5-4-2 (A) of the Prescott ordinance needs only to replace "heard" with "plainly audible" (there is a difference) to be equivalent.

In summary, with the acquisition of sound level meters, Prescott will have the tools to solve community noise problems.

Dr. Chanaud received his bachelor of science degree in engineering from the U.S. Coast Guard Academy, his master of science degree in engineering from the University of California, and his Ph.D. in engineering from Purdue University. His area of specialization is acoustics. He has been active in the field since 1958. He was a consultant to the Environmental Protection Agency on community noise problems and assisted a number of communities to develop noise ordinances. He was one of the authors of the EPA Model Noise Code and is now is retired in Prescott.


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