The Acoustics Facility of the Volpe National Transportation Systems Center (part of the Research and Special Programs Administration of the U.S. Department of Transportation), in support of the Federal Railroad Administration, is conducting safety research to evaluate the effectiveness of various methods of reducing the number of accidents and resulting casualties at highway-railroad grade crossings. As part of this research, the effort reported here evaluates the probability of detecting railroad horn systems used as audible warning for motorists at highway-railroad grade crossings. To evaluate the detection probability, three sets of acoustic data were collected: ( a) acoustic characteristics of railroad horns, including sound level and directivity; ( b) insertion loss of motor vehicles; and ( c) baseline interior noise levels of motor vehicles. These data were used to determine the warning-signal-level-to-interior-noise-level ratio inside the motor vehicle at the minimum distance that would give the motorist sufficient time to react and avoid a collision. Signal detection theory, which incorporates the motorist’s prior expectations of encountering a train, is then applied to estimate the probability of detecting three currently used railroad horn systems at active and passive grade crossings.

To evaluate the relationship between aircraft noise exposure and the quality of national park visitor experience, more than 4600 visitor surveys were collected at seven backcountry sites in four U.S. national parks simultaneously with calibrated sound level measurements. Multilevel logistic regression was used to estimate parameters describing the relationship among visitor responses, aircraft noise dose metrics, and mediator variables. For the regression models, survey responses were converted to three dichotomous variables, representing visitors who did or did not experience slightly or more, moderately or more, or very or more annoyance or interference with natural quiet from aircraft noise. Models with the most predictive power included noise dose metrics of sound exposure level, percent time aircraft were audible, and percentage energy due to helicopters and fixed-wing propeller aircraft. These models also included mediator variables: visitor ratings of the "importance of calmness, peace and tranquility," visitor group composition (adults or both adults and children), first visit to the site, previously taken an air tour, and participation in bird-watching or interpretive talks. The results complement and extend previous research conducted in frontcountry areas and will inform evaluations of air tour noise effects on visitors to national parks and remote wilderness sites.

An analysis of visitor survey responses and concurrent noise exposure was performed using data from ten sites in four scenic U. S. National Parks. Data collection was structured to learn the effects of air-tour aircraft noise and high-altitude jet noise on the experience of park visitors at scenic overlooks and on short hikes. The analysis utilized multilevel logistic regression and resulted in six doseresponse relations: two responses (annoyance and interference with natural quiet), paired with three response dichotomizations (slightly or more, moderately or more, and very or more). Each of those six relations retained the same set of regression predictors. Individual-visitor Leq from all aircraft (averaged over the visitor duration at the site) proved to be the most reliable/accurate predictor of all noise dose metrics tested. The relation with visitor Leq was significantly strengthened by inclusion of three additional dose-related predictors: the energy-percentage due to tour helicopters for each visitor, the same due to fixed-wing tour aircraft, and the interaction of these two percentages. In addition, the relation was also strengthened by inclusion of the following context variables: Scenic overlook or short hike, natural quiet very important (or not) to that visitor, visitor group includes only adults (or not), and first-time visit at that site (or not). For a given noise exposure, visitors expressed more negative response regarding interference with natural quiet than regarding annoyance. In addition, visitor response to a given dose of air-tour noise was less severe when there were low-to-moderate levels of high-altitude jet noise present. V C 2011 Institute of Noise Control Engineering.

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