Corridor shakeout

Case Studies
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The Idaho Transportation Department (ITD) and David Evans and Associates Inc. commissioned the use of the Trimble Quantm Alignment Planning System to:

  • Generate and screen alternatives for a new highway segment bypassing Goose Creek Canyon (a steep, sharp-curved roadway), including upgrading of the existing highway or providing a new, 4- to 7-mile route to improve safety on SH 55, between the towns of New Meadows and McCall, Idaho; and
  • Simultaneously analyze complex engineering and environmental issues for highway corridor analysis.

The purpose of the project was to construct a safe, economical and environmentally acceptable highway around Goose Creek Canyon. Bypassing Goose Creek Canyon would avoid many physical problems, including a narrow 22-ft-wide roadway, steep 7% grades, shaded areas due to lack of sun exposure that can lead to frequent icing conditions in winter, poor curvature, low driving speeds and inadequate passing opportunities.

ITD and David Evans and Associates Inc. used the planning software to screen alternatives and select two highway corridors for further National Environmental Policy Act (NEPA) evaluation. In doing so, they developed a process to screen alternatives that addressed the challenges for determining new highway corridor alternatives. This was achieved by:

  • The ability of the software to ensure comparisons on location, impact on environment, cost and compliance with engineering criteria;
  • The software demonstrating that it was cost prohibitive to attempt to comply with current design standards by modifying the existing route within the canyon;
  • Quickly changing the environmental and engineering criteria and generating new alignments that the team could review within days. The software made it easier to objectively consider new alternatives suggested by the project stakeholders throughout the screening process by eliminating labor- and cost-intensive manual processes;
  • Generating new alternatives rapidly and making it easy to demonstrate to agencies that their views are integrated;
  • Using the planning system to define highway corridors to limit the areas for intensive environmental field work and still provide a product that will comply with NEPA; and
  • Highlighting where constraints could not be met and presenting how changes affect cost in an unbiased way.

Quantm’s ability to demonstrate a comprehensive investigation of alternatives, both across the whole terrain model and in focused areas, ensured the project would meet the engineering, social and environmental criteria defined by the team.

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