US Highway 95 is the major north-south transportation artery for both tourism and commerce in Idaho. The Worley to Mica Creek Corridor, a 20-mile segment of US 95 in north Idaho, was considered one of the most dangerous segments of this route in the state, with accident rates higher than the statewide average. The existing narrow, winding two-lane highway had dangerous sharp curves, steep grades, and limited sight distance. In several areas, the highway was substantially shaded by both hills and timber, creating icy conditions in the winter. The purpose of the US 95 Worley to Mica Creek project was to improve the alignment of this segment of US 95 to safely accommodate projected traffic and to maintain the viability of this route for local, commercial, and recreational traffic, while minimizing or eliminating adverse environmental, economic and cultural impacts. The project eliminated the nonstandard highway alignment and provided a safer, four-lane divided roadway.

Throughout the project development process, a collaborative decision making process was implemented with stakeholders and regulatory agencies to successfully represent the interests and needs of each group. A significant portion of the corridor is inside the Coeur d’Alene Indian Reservation, and the area is an important part of the Tribe’s cultural heritage. As such, particular attention was given to identify cultural resources of significance to the Tribe, and to be sensitive to those resources in the design of the project.

Preservation of natural resources was a fundamental part of the design process to fit the highway to the natural setting. Several measures were incorporated into the project design to avoid or minimize adverse environmental impacts. During construction, the contractor was allowed to remove only the minimum amount of timber needed for roadway construction. Clearing and grubbing was limited to 3 meters beyond the grading limits, and earth-disturbing activities were limited to 6-month windows to control the potential for erosion. A tribal member also was present during the first meter of excavation to monitor for potential items of cultural significance. The project site had highly erodible slopes that were stabilized with natural rock mulch to provide for vegetation growth while preventing erosion.

Retaining walls were used extensively in the South Fork Mica Creek canyon to avoid impacts to sensitive areas along the South Fork Mica Creek, and to minimize the extent of excavation required in the canyon segment. Welded wire mechanically stabilized earth (MSE) retaining wall systems were determined to be the best solution for this project because of their ability to accommodate potential differential settlement, and because welded wire walls provide an aesthetic and economical wall system. A facing of natural crushed basalt was used in the retaining walls to blend with rock outcroppings found in the area.

Bridges were designed at several new stream crossings to accommodate anticipated flows, to protect natural vegetation, and to allow big game passage under the highway. Complex temporary measures were specified to protect the sensitive natural environment of these areas. Temporary stream crossings were required for constructing some of the structures. Environmentally sustainable solutions for these temporary stream crossings included placing chain link fence material with a geotextile fabric over the existing vegetation to aid in the subsequent removal of the fill material. A temporary culvert placed in Lake Creek during bridge construction was designed to maintain a minimum water depth to ensure unobstructed fish passage at all times. Two new box culverts were designed with a series of fish baffles holding streambed gravel in place to facilitate fish passage. Permanent restoration of disturbed areas included use of coir log toe-of-slope protection in the channel and riparian plantings to restore the site to a natural condition and to control the potential for erosion.

The partnering relationship used on this project provided the framework for an efficient and proactive project development approach, and adherence to the project schedule. The completed project successfully meets identified transportation needs while balancing diverse stakeholder interests and minimizing environ¬mental impacts. Close collaboration with federal and state regulatory agencies, the Coeur d'Alene Tribe, and the public helped create context sensitive solutions for US 95 that will serve the region well into the future.