For the week of August 27 - September 2, 2003

Noise study
finds highway
acceptable, mostly

Five or more valley locations
may need berms, walls

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By GREGORY FOLEY
Express Staff Writer

A consultant to the Idaho Transportation Department has determined that a proposed expansion of Highway 75 through the Wood River Valley would not require extraordinary efforts to mitigate noise, but some noise barriers may be needed.

Representatives from Utah-based Parsons Brinckerhoff, which is assisting ITD in analyzing two competing highway proposals, said last week that five areas of the highway corridor currently exceed a 67-decibel federal standard for exterior noise around residential areas and public spaces.

However, Diana Atkins, Parsons Brinckerhoff project manager, said projected noise levels in future years from two competing highway-expansion proposals are generally not significantly higher than existing conditions, and in some areas are lower.

ITD is currently evaluating two project proposals that would have the same lane configurations and same physical footprint on the landscape. The two proposals would include four and five traffic lanes through much of the 27-mile stretch from Timmerman Hill—at the highway’s junction with Highway 20—to Ketchum. However, one design would include designated high-occupancy-vehicle commuter lanes while one would not.

ITD and PB in 2002 and early 2003 conducted a study of noise levels at 71 locations throughout the highway corridor. The locations represented 710 residences located near the existing highway.

"Noise modeling results show that existing noise levels approach or exceed the (federal and state) criteria in five locations in the corridor, representing approximately 40 residential units," Atkins said.

The five locations that currently exceed the 67-decibel limit are all located between Hailey and Ketchum. They include residences adjacent to the highway immediately north of Hailey, two mobile-home communities and four homes between Gimlet subdivision and the highway’s intersection with Broadway Run, and a set of rental cabins immediately north of the Broadway Run intersection.

Lawrence Spurgeon, lead environmental engineer for PB, said that a "handful" of additional locations in the Wood River Valley could in the future exceed the federal limit, with or without highway improvements. He noted that he is continuing to research what locations might exceed 67 decibels by 2025.

Downtown Bellevue is on the cusp of exceeding the limit, but would not be a practical location for mitigation measures, Spurgeon said.

Throughout the highway corridor, noise levels projected in 2025 generally exhibit an increase in only one to four decibels from those that exist today. "It takes a pretty large change in the volume of traffic to get a significant decibel change," Spurgeon said.

Because highway noise is largely related to traffic speeds, projected noise levels in some instances are projected to drop slightly in relation to speed-limit decreases planned as part of the two expansion proposals.

Atkins said PB and ITD have not yet determined whether mitigation measures will be proposed for the locations that exceed the federal noise standard. She said ITD and PB, in drafting an environmental-impact statement on the expansion project, will consider using berms and walls to mitigate noise. She said ITD will have to consider whether a barrier would be effective, whether it obstructs any existing property access points, and whether it would exceed a construction-cost limit of $20,000 per affected residence.

Atkins said affected property owners would be consulted. "The evaluation includes both technical and social considerations, such as if a mitigation measure would be effective and if the local residents in the area … desire it."

 

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