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CHAPTER 10. NOISE OVERVIEW Any undesirable sound can be considered noise. Vehicle engine, vehicle exhaust, tire-pavement interaction, locomotive engine and exhaust, locomotive horn, train wheel-track interaction, and jet engine noises all result from everyday transportation activities. These noises also are among those most often cited as causing the highest levels of annoyance. Various transportation modes can generate sound levels great enough to cause hearing loss and tinnitus (i.e., ringing in the ears). It is unlikely, however, that very many people will be exposed long enough to experience actual hearing loss or damage, except in the workplace environment. Health effects are therefore not the most common transportation noise issue. A much more common concern is the annoyance that persistent noise causes for individuals living, working, or participating in other daily activities near transportation facilities. The FHWA and the FTA have developed methods to determine project noise levels and whether these levels are significant enough to be defined as an impact. The results of these standard methods can readily be used to perform environmental justice assessment. Impacts can occur either as a result of noise level increases or of threshold exceedance. The impact criteria adopted by FHWA and FTA have been developed over time and are based on surveys and research on annoyance and aggravation. Both the FHWA and FTA use impact level as an indication that noise mitigation should be considered. The FTA has stratified impact levels into three classifications: no impact, impact and severe impact. In general, environmental justice assessments of distributive noise effects should use these standard impact classifications and threshold levels only as a starting point. Evaluating the level of effects against standard thresholds is not acceptable as a final determination of "adverse effect" as the term is used in this guidebook. Perceptions of what constitutes an adverse noise effect can vary considerably from individual to individual and from community to community. For transportation projects, the noise impact criteria are therefore not designed to be absolute. Rather, the criteria may be used as a guide to determine whether levels of an effect must be mitigated according to regulation. Various methods are used to evaluate project noise level increases and net project noise levels. The FHWA and FTA have slightly different methods, and each can be used to evaluate distributive effects to protected populations. Results of both FHWA and FTA noise assessments commonly indicate the number of sensitive receptors (locations at which noise is measured) that would experience an impact (e.g., 57 residences). Thus, analyses usually are performed at discreet locations within the study area. In some instances, noise level contours are used to determine the number of receptors. Both contour-based and receptor-based results can be used to evaluate distributive effects to protected populations. It can generally be expected that receptors near a project will incur the greatest noise level increase and sustain the greatest net noise level. Noise impacts of road and rail construction and operation are localized, and normally are experienced at the first row of houses or properties 231