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This paper presents the results of a statewide noise barrier study for the New Hampshire Department of Transportation (NHDOT). The feasibility and reasonableness of noise barriers throughout the state has been evaluated according to NHDOT acoustical and cost-effectiveness criteria. The study has provided the DOT with an estimate of the potential noise barrier material costs associated with a newly implemented Type II noise barrier program. The study also has identified municipalities that the DOT can coordinate with for enacting noise-compatible planning regulations. The paper describes the methodology used to develop the screening-level noise barrier evaluation. Highway noise levels throughout the state and the distances from the highway where noise levels exceed the noise abatement criteria were determined. A method to predict the noise reduction of barriers (insertion loss) based on a simple geometrical relationship of receptors and potential noise barriers was established and has been shown to correlate well to detailed traffic noise models using actual roadway and terrain geometry. The simplified prediction method was used to evaluate over 300 miles of highway, 300 candidate noise barrier study areas, and over 30,000 receptors. This screening-level modeling approach is critical to the practicality of using the Traffic Noise Model across the entire state given the significant number of receptors and noise barrier study areas. The results of the study including information about all 30,000 receptors and 300 noise barrier study areas were collected in Google Earth™ data files for easy access when the DOT responds to noise complaints from the public.

The Virginia Department of Transportation (VDOT) currently designs absorptive sound barriers with their entire face absorptive [noise reduction coefficient (NRC) of 0.8 or greater]. Using the FHWA Traffic Noise Model, the sound level increases caused by three modifications to current VDOT practice were investigated: a more reflective barrier surface (NRC = 0.7), a 6-in. (15-cm) reflective cap, and a 2-ft (61-cm) reflective base. These increases were computed for receivers up to 40 ft (12.2 m) above the ground and 1,000 ft (305 m) behind the barrier. The computations included three barrier locations—barrier opposite receivers, barrier same side as receivers, and barriers on both sides—at several barrier heights and distances from the roadway. They also included two roadway widths and two traffic conditions, to span the extreme ranges of these variables. Results indicate that for a barrier opposite the receivers, the more reflective surface caused a maximum increase of 1.3 dB, the 2-ft (61-cm) reflective base caused a maximum increase of 1.7 dB, and all three modifications combined inflated this increase to 2.7 dB. For a barrier on the same side of the roadway as the receivers, no situations caused increases greater than 1 dB. Finally, for barriers on both sides of the roadway, the more reflective surface caused a maximum increase of 1.1 dB, and all three modifications combined inflated this increase to 1.5 dB. A table of resulting sound level increases for the full field of computed receivers—for the worst-case situations encountered in the computations—is included.

It is estimated that up to 9.3 million persons may be impacted by locomotive horn noise and up to 4.6 million of those may be severely impacted.1 In 2009, there were over 1,900 incidents, over 700 injuries and over 240 fatalities at highway-rail grade crossings.2 The National Academy of Engineering Committee on Technology for a Quieter America has indicated that the public would benefit if train warning horns were more directional and has recommended that research and development be undertaken to better understand the effects on safety and benefits to the public.3 A directive train horn has the potential to focus audible warning signals to desired locations including pedestrians and motorists at highway-rail grade crossings while minimizing noise to the surrounding community and employees in the locomotive cab. As a part of an ongoing Federal Railroad Administration (FRA)-sponsored research and development effort, the authors have examined the feasibility of and recommended an acoustical specification for an optimized train horn that would improve the detectability of the warning signal for motorists at critical positions along the crossing road while reducing the area of environmental noise impact. The detectability, noise impact area and occupational noise exposure have been compared for the optimized horn and several typical standard horns. Near the beginning of most sounding events (1/4-mile from the grade crossing) the optimized horn reduces noise exposure because a narrow beam of sound can be generated and focused at the grade-crossing. As the train approaches the crossing, the beam width must become wider. It is found that detectability could be improved and noise impact area reduced by up to 57%, but the optimized horn must have a directivity pattern and amplitude that dynamically changes as a function of train position relative to the crossing. Current acoustic source technologies which generate directive sound were examined including “acoustic hailing devices” (AHDs) which are recent technological advancements typically used for naval communications. Capable of focusing high amplitudes of sound within a narrow beam and dynamically changing the directivity pattern through electronic beam steering, AHDs have been identified as a feasible means of meeting the required specifications. A critical design issue for the optimized horn is controlling the directivity pattern at low frequencies. Development and testing of a prototype is in progress and actual improvements to detectability and reductions in noise impact will be analyzed. The paper briefly discusses the feasibility of the optimized horn and general information on cost and implementation.

The U.S. National Park Service is concerned about the effect that noise from snowmobiles and other over-snow vehicles has on the natural soundscapes in the National Parks. This paper addresses the measurements and modeling performed to assess both the total area in the parks where snowmobile noise would be audible and the noise intrusiveness as a function of distance from the trails. The work was performed in support of an Environmental Impact Statement that evaluated seven operational transportation alternatives in the two parks. The modeling approach computed both A-weighted sound levels and audibility continuous time histories of snow-vehicle noise at several distances from the trails. Acoustical input to the model included 1/3-oct band levels for ambient conditions, vehicle source levels, and propagation of sound over a snow-covered surface. Consequently, distances to the onset of audibility detection, areas of the parks affected, and statistics on received sound levels were calculated. The paper presents both the modeling approach and examples of results.