Sterling Highway Underpasses
Alaska
Road: Alaska Route 1 - Sterling Highway
Structures: Six underpasses (five culverts, one bridge)
Target Species: Moose
Every year on Alaska’s Kenai Peninsula, as many moose are killed in wildlife-vehicle collisions (WVCs) as are harvested by hunters. That’s a real shame in a state where healthy wildlife populations and the ability to hunt for subsistence has been the Alaska Native way of life for time immemorial and remains foundational to Alaska’s character today. The societal cost of those collisions -- in damaged or totaled vehicles, human injuries or fatalities and the monetary value of each animal, among others -- averages $7‒9 million dollars annually, not to mention the cost to the regional ecosystem.
Between mileposts 58 and 79, Alaska’s Sterling Highway winds through the U.S. Fish and Wildlife Service’s (USFWS) Kenai National Wildlife Refuge. Highway traffic creates a major barrier to moose and other species attempting to move north and south between patches of habitat. When Alaska Department of Transportation and Public Facilities (AKDOT&PF) proposed upgrading this stretch of highway, wildlife mitigation measures were needed to protect the future of the region’s wildlife, particularly moose, as traffic and operational speeds increased.
As part of the highway improvement project, six wildlife underpasses were installed. Five are culverts of various sizes, including one dual culvert. One existing 10’ culvert that had previously allowed only the water of a creek to pass through was replaced with a 135’ bridge that now allows animals of all sizes to move along this rich riparian corridor. To reduce the high number WVCs along one particularly problematic section of highway, fencing runs between the new bridge undercrossing and the dual culvert two and a half miles to the west. A nine-foot-tall fence with a one foot gap at the bottom funnels moose and other large, far-ranging mammals to the dual culvert and the bridge undercrossing, while enabling smaller animals to pass underneath the fence and cross the road at will. For wildlife that find themselves on the roadway on the wrong side of the fencing, jumpouts are located every ⅛ of a mile.
Underpass locations were selected using moose GPS collar data, local knowledge of species movement, and topography. A large fire burned through the area during construction, changing regional vegetation entirely, emphasizing the importance of diverse criteria for crossing location selection, rather than relying solely on existing vegetation and related collar data.
Kenai National Wildlife Refuge, AKDOT&PF, Alaska Department of Fish and Game, Federal Highway Administration, Alaska’s Department of Public Safety and Alaska Moose Federation worked collaboratively to make this project a reality. The project represents many firsts for Alaska including the first wildlife crossing infrastructure outside of an urban area, the first use of certified weed-free gravel, and the first time AKDOT&PF has taken responsibility for managing roadside invasive plants. The success of this project also paved the way for the Cooper Landing Bypass project which will include two more underpasses on the Kenai National Wildlife Refuge as well as Alaska’s first wildlife overpass.
Wildlife mitigation measures accounted for $10.5 million of the $71 million dollar project cost. Project funding was contributed by the AKDOT&PF, the USFWS Refuge System, and a Federal Lands Access Program (FLAP) grant. The Kenai Refuge contributed some gravel from an old pit and, in exchange, the pit is being rehabilitated as part of the project.
