Trimble Alignment Planning: A highway corridor planning process for NEPA compliance

"ITD and David Evans and Associates, Inc with the assistance of the Trimble Alignment Planning system have implemented a highway corridor planning / environmental / engineering process to establish highway corridors and select alternatives that will comply with NEPA regulations. This process can address many of the challenges found in the highway environmental process by being objective, comprehensive, cost-effective, and quicker than conventional methods."
David Evans and Associates, Inc. and Idaho Transportation Department

The Idaho Transportation Department (ITD) and David Evans and Associates, Inc. commissioned the use of the Trimble Alignment Planning system to:
a) screen alternatives for the new highway segment that would bypass Goose Creek Canyon (a steep, sharp- curved roadway), including upgrading of the existing highway or providing a new, four to seven-mile route to improve safety on SH 55, between the towns of New Meadows and McCall, Idaho.
b) simultaneously analyze complex engineering and environmental issues for highway corridor analysis.

The purpose of the project is to construct a safe, economical, and environmentally acceptable highway around Goose Creek Canyon. Bypassing Goose Creek Canyon would avoid many physical problems including: narrow 22-foot wide roadway, steep 7 percent 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 Trimble Alignment Planning to screen alternatives and select two highway corridors for further NEPA evaluation. In doing so, they developed a process to screen alternatives that addresses the challenges for determining new highway corridor alternatives. This was achieved by:

• The ability of the Trimble Alignment Planning system to ensure comparisons on location, impact on environment, cost and compliance with engineering criteria.
• Trimble Alignment Planning demonstrating that it was cost prohibitive to attempt to comply with current design standards by modifying the existing route within the canyon.
• Quickly change the environmental and engineering criteria and generate new alignments that the team could review within days (making it no longer labor and cost intensive to objectively consider new alternatives that may be suggested by the project stakeholders throughout the screening process).
• Generating new alternatives rapidly. Making it is easy to demonstrate to agencies that their views are integrated.
• Using the Trimble Alignment Planning system to define highway corridors to limit the areas for intensive environmental field work and still provide a product that would comply with NEPA.
• The ability to demonstrate a comprehensive investigation of alternatives, both across the whole terrain model and in focused areas. The Trimble Alignment Planning system highlights where constraints cannot be met and presents the alignment and how changes affect cost in an unbiased way.

Figures 1, 2, 3 and 4 show how Trimble Alignment Planning can be used to define a highway corridor. The eight alternatives shown in figure 1 served as the basis to define preliminary corridors for further NEPA analysis. The eight alternatives were run again through the Trimble Alignment Planning optimization engine, using a "seeded optimization" to generate a new array of alternatives in close proximity to each of the previous eight