Idaho State Highway 16 Extension

The first phase of the future Central Valley Expressway connecting seven cities in Idaho to Interstate 84.

GeoEngineers led geotechnical design and provided construction support services to connect state Highway 44 and US Highway 20/26 in Treasure Valley near Boise, ID. This project is the first phase of the future Central Valley Expressway that will connect seven cities to Interstate 84.

GeoEngineers, as part of a design team selected by the Idaho Transportation Department and Connecting Idaho Partners, completed explorations in sensitive wetland areas, analyzed deep pile foundations and prepared both flexible and rigid pavement designs. GeoEngineers also provided investigations and reports for Materials Phases I, II, II, IV and V.

In addition to a two-mile extension of state Highway 16, the project created a new 11-span, 1,800-foot long bridge over the Boise River, the first new river crossing in the area in 20 years. The bridge is expected to serve 22,000 cars a day, thereby reducing congestion and decreasing response times for emergency service vehicles.


The main challenge of the project was doing geotechnical exploration in an environmentally sensitive area that included a flood plain and nesting area for bald eagles and wild turkeys. To protect the sensitive areas, GeoEngineers took extra measures to contain all drilling mud on site and revegetate affected areas. The project team also coordinated with private landowners to gain access to areas of the project site as needed, and took care to leave private property in good condition.


GeoEngineers completed the project ahead of the client’s schedule, which was tight for a project of this scope. Project completion for this phase of the Central Valley Expressway completed in fall 2014 and includes:

  • A two-mile expansion of state Highway 16
  • Eight miles of new local roads
  • Numerous irrigation crossing structures
  • Two mainline intersections
  • Two bridges, including a single-span road crossing and an 11-span bridge over the Boise River

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