EXHIBIT 4-2_55A_BRISTOL WIDENING TECHNICAL STUDIES

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change in Community response (i.e. complaints) would be ex- pected. l Recent studies have shown that changes in long -term noise levels, measured in units of Ldn or CNEL, are noticeable and that people respond. About 10 percent of the people exposed to traffic noise of 50 Ldn will report being highly annoyed with the noise, and each increase of one Ldn is associated with approximately 2 percent more people being highly annoyed. When traffic noise exceeds 60 Ldn or aircraft noise exceeds 55 Ldn, people begin complaining. Group and legal actions to stop the noise should be expected to begin at traffic raise levels near 70 Ldn and air- craft noise levels near 55 Ldn. Land Use Compatibility with Noise Some land uses are more tolerant of noise than others. For example, schools, hospitals, churches and residences are more sensitive to noise intrusion than commercial or industrial I activities. As ambient noise levels affect the perceived amenity noise impacts impair the economic health and growth potential, of a community by reducing the area's desirability as a place to live, shop, and work. For this reason, land use compatibility with the noise environment is an important consideration in the planning and design process. There are two sets of noise criteria that apply to the Bristol Street widening project. These include the federal noise stan- dards (promulgated by the Federal Highway Administration) and the City of Santa Ana noise standards established in the Noise Ele- ment of the General Plan. Each set of criteria uses a different noise metric and a unique methodology to assess noise impacts. Federal Standards: The Federal Highway Administration (FHWA) has developed a series of design noise levels for various activity categories which are expressed in terms of equivalent sound levels (Leq) or Llp values.3 These design noise levels are commonly used on federally funded projects or projects for which federal review or CalTrans review is anticipated. The FHWA. design noise levels represent maximum values and incor- porate trade -offs between desirable and feasible noise levels (recognizing that in many cases lower noise exposures would I. "Noise Manual ": Caltrans, 1980 and "National Cooperative Highway Research Program Report 117 ", HRB, 1971. 2. State of California, Department of Health Services, Dr. Jerome Lukas, Memo dated July 11, 1984. 3. LI0 values are noise levels exceeded ten percent of the time. They are commonly used to express peak hour noise levels (since peak hour traffic volumes are typically 10 percent of the daily traffic volume). 4 -3