Assessing Community Annoyance of Helicopter Noise (2017)

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128 A long-standing approach to the problem of accounting for variability in judgments of the annoyance of fixed-wing aircraft noise has been to develop new noise metrics. This approach has produced a veritable alphabet soup of noise metrics, but no appreciable improvement in understanding or predictability of annoyance caused by fixed-wing aircraft noise. Nonetheless, it remains plausible that some improvement in predicting the annoyance of helicopter noise can be achieved via more complex noise metrics alone. After all, helicopter noise can be far more complex than the noise of fixed-wing aircraft. For practical purposes, a technically defensible answer to the question “Are people more annoyed by helicopter than by fixed-wing aircraft noise?” requires answers to several further questions. Assuming for purposes of discussion that all other things being equal, helicopter noise is more annoying than aircraft noise, the first of these additional questions is whether any observed differences in annoyance prevalence rates are due to acoustic or nonacoustic factors. Given the extent to which communities differ in their opinions about the annoyance of expo- sure to fixed-wing aircraft noise, it is likely that they also differ widely in their opinions about the annoyance of exposure to rotary-wing aircraft noise. Figure C-1 shows the scatter in prior measurements of the relationship between aircraft noise exposure and the prevalence of a con- sequential degree of annoyance in communities. Each data point shows the percentage of sur- vey respondents who described themselves as “highly” annoyed (usually, “very” or “extremely” annoyed) by aircraft noise. The range in noise exposure levels that give rise to the same prevalence of annoyance is on the order of 60 dB. The range in annoyance prevalence rates for the same exposure level across all transportation modes extends from none to about 90%. Figure C-2 shows that the correlation is particularly poor in the range of greatest regulatory interest, from 55 to 75 dB. C.1 Definition of Community Tolerance Level Fidell et al. (2011) have shown that a nonacoustic measure known as the CTL, in conjunc- tion with cumulative noise exposure per se, accounts for half again as much of the variance in aircraft noise-induced annoyance prevalence rates from one community to the next as noise exposure alone. CTL is formally defined in a Final Draft International Standard 1996-1, shortly to be adopted as an ISO standard. A CTL value is a level of DNL at which half of a community is highly annoyed by noise exposure, and half is not. Since field studies of the prevalence of noise- induced annoyance in communities do not often directly measure DNL values at which half of a community is highly annoyed, it is necessary to estimate CTL values in another way. CTL-based predictions of annoyance prevalence rates are based on the observation that the annoyance of transportation noise exposure grows at a rate very similar to the rate of growth of A P P E N D I X C Systematic Analysis of Nonacoustic Influences on Annoyance

Systematic Analysis of Nonacoustic Influences on Annoyance 129 duration-adjusted (“effective”) loudness with sound level. Fidell et al. (2011) and Schomer et al. (2012) show that the fits of social survey data sets to effective loudness predictions can be found by first converting DNL values for interviewing sites in the same community into a noise dose, m, calculated as m = (10(DNL/10))0.3. Annoyance prevalence rates for the calculated dose are then predicted as p(HA) = e–(A/m), where A is a nonacoustic decision criterion originally defined by Fidell, Schultz, and Green (1988). The dose parameter, m, controls the rate of growth of annoyance on the ordinate of a dosage-response relationship, while the decision criterion parameter, A, translates the growth function along the abscissa. The value of A for a given community is estimated by minimizing Figure C-1. Relationship between FICON curve and field measurements of DNL and the prevalence of high annoyance for all modes of transportation noise. DAY-NIGHT AVERAGE SOUND LEVEL, dB PR EV A LE N CE O F H IG H A N N O YA N CE , % Figure C-2. Poor correlation between exposure and response in exposure range of greatest pragmatic concern.

130 Assessing Community Annoyance of Helicopter Noise the root-mean-square error between observed and predicted percentages of highly annoyed survey respondents (Green and Fidell, 1991; Fidell et al., 2011). C.2 Communities Form Unique Attitudes About Noise Communities exposed to similar aircraft noise show a wide variance in attitudes about that noise. It is from this observation that the conclusion is made that the focus of understanding annoyance is better done on the community level rather than the individual level. The panels of Figure C-3 (Fidell, 2011) display the fit of the findings of several social surveys to the effec- tive loudness function. Each data point shown in these panels represents a paired observation of the prevalence of high annoyance among respondents at an interviewing site with the site’s aircraft noise exposure level. The solid portion of the effective loudness function in each panel of Figure C-3 is the range of primary interest for policy and regulatory purposes. The dashed extensions show the behavior of the function outside the range of primary interest. Not all of the data sets fit the effective loudness function as well as the examples shown in Figure C-3 panels a–f. On average, however, the effective loudness function built into the CTL calculation Figure C-3. A comparison of CTL values for six airports showing that at similar noise exposure levels the rate of annoyance varies over a wide range.

Systematic Analysis of Nonacoustic Influences on Annoyance 131 accounts for two-thirds of the variance in the association of observed and predicted annoyance prevalence rates. C.3 Application of CTL Analysis to Annoyance of Exposure to Helicopter Noise CTL values directly comparable to those calculated for the Fidell et al. (2011) surveys can also be calculated for interviewing sites that are exposed to a range of helicopter noise exposure conditions. Calculating CTL values for the proposed sites would make it possible to make consis- tent comparisons of the annoyance of rotary- with fixed-wing aircraft noise. These comparisons could be made both with respect to new social survey findings, and with respect to the Fidell et al. (2011) database for aircraft and the Schomer et al. (2012) database for road and rail noise.24