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ID-21, Cervidae Peak Wildlife Overpass

The overpass will significantly reduce wildlife-vehicle crashes on this busy highway

The Idaho Highway 21 (ID-21) Wildlife Overpass at Cervidae Peak project proposes to construct an approximately 120’ to 150’ long wildlife overpass over the highway at mile point (MP) 19.32. The project will also construct big game fencing parallel to ID-21 from MP 18.4 to MP 19.6 to guide animals to the overpass.

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ID-21 Vision

This is the next step in the long-range vision to promote safety, mobility, and economic opportunity along ID-21 between Lucky Peak and Idaho City. In conjunction with the existing wildlife underpass and fencing to the south, this project will further reduce the number of wildlife-vehicle collisions and maintain habitat connectivity for big game.The goal is to reduce wildlife collisions from MP 18.4 to MP 19.6 highway by 80%.

Environmental Analysis

The project team, including Idaho Transportation Department, Idaho Department of Fish and Game, and Western Federal Lands Highway Division, is currently completing an environmental analysis of the project. The project goals include:
• Work only on public lands and not acquire additional right of way
• Preserve access to adjacent public lands
• Use natural topography to reduce construction costs and impacts to habitat
• Keep impacts to viewshed minimal

Overpass & Fencing Design

The overpass is expected to be 120-150′ long. It will utilize existing terrain to reduce costs and impact to the topography.

Big game fencing on either side of the overpass will funnel wildlife to the crossing. Its placement will consider terrain, constructability, future maintenance and avoid impairing views from the road.

Wildlife Crossing Record of Success

In 2010, ITD constructed a grade-separated wildlife underpass on ID-21 at MP 18.2. Game cameras monitoring that underpass show extensive use  by mule deer, elk and other wildlife – all of which pose serious safety and mobility hazards to drivers if they were on the road. This also improved habitat linkage and landscape connectivity to the Boise River Wildlife Management Area and adjacent public lands of the Boise National Forest, U.S. Army Corps of Engineers, Idaho Department of Lands, City of Boise and Bureau of Land Management.

Cooperative Support

As ITD developed this project, it received support from Idaho Department of Fish and Game, U.S. Forest Service, Army Corps of Engineers, the City of Boise, Ada and Boise Counties, numerous Non-Governmental Organizations, and the Western Federal Lands Highway Division (WFLHD) of the Federal Highways Division. Investment in these improvements supports the varied missions of these agencies to serve the citizens and taxpayers of Idaho.


This project is funded through the Federal Lands Access Program (FLAP) and provides $3.2 million to reduce wildlife-vehicle collisions while maintaining or enhancing habitat and landscape connectivity to Federal lands. Local match was required for this program and was provided by the diverse group of agencies and organizations mentioned above.

View the FLAP application here


**All contact information will be kept confidential,
but all comments will be publicly visible**
Interactive Comment Map

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View Map
FLAP submission
Environmental analysis begins
Spring 2020
Design begins
Late 2021
Environmental analysis complete
Late 2021
Design complete
Summer 2022
Anticipated Construction Start
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