The World’s Largest Wildlife Overpass is Halfway Complete

In the heart of Colorado’s Douglas County, a groundbreaking project is taking shape along Interstate 25 near the Greenland Interchange between Monument and Larkspur. The Greenland Wildlife Overpass, poised to become the world’s largest wildlife overpass upon its completion, represents a bold effort to harmonize human infrastructure with the needs of wildlife. According to officials, the project is now halfway complete, marking a significant milestone in Colorado’s commitment to reducing wildlife-vehicle collisions and preserving critical migration corridors.

The origins of the Greenland Wildlife Overpass trace back to growing concerns over the safety of both drivers and wildlife along the I-25 corridor, a vital artery connecting Denver and Colorado Springs. This 18-mile stretch, known as the I-25 South Gap, sees approximately 85,000 daily trips, a number projected to soar to 150,000 by 2040. The area is a hotspot for wildlife-vehicle collisions, averaging one crash per day during peak migration seasons. These incidents pose risks to human lives, cause significant property damage, and threaten the survival of species like elk, mule deer, pronghorn, bears, and mountain lions.

Recognizing the need for action, the Colorado Department of Transportation (CDOT), in collaboration with Colorado Parks and Wildlife (CPW), the Federal Highway Administration, and Douglas County, began planning a comprehensive wildlife crossing system as part of the $450 million I-25 South Gap improvement project. Data on elk herd movements and collision hotspots pinpointed the Greenland Interchange as an ideal location for a major crossing. The overpass would bridge a 3.7-mile gap in existing crossings, connecting 39,000 acres of big game habitat in Douglas County to over 1 million acres of the Pike National Forest.

The project gained momentum with funding from the Bipartisan Infrastructure Bill, which prioritized wildlife-friendly infrastructure. In 2022, CDOT awarded the construction contract to Kraemer North America, a firm already working on the I-25 South Gap project. Their surprisingly low $15 million bid for the overpass itself, was attributed to economies of scale and prior mobilization. Construction on the overpass began in 2023, and now has an aggressive target completion date of December 2025.

The Greenland Wildlife Overpass is an engineering marvel designed to blend seamlessly with its natural surroundings. Spanning six lanes of I-25, the structure measures 209 feet long and 200 feet wide, covering nearly 80,000 square feet. Its gentle inclines and soil-covered surface, soon to be planted with native vegetation, will create a natural pathway for wildlife. Unlike narrower underpasses, which are better suited for smaller animals, the overpass’s wide, open design offers better visibility for large game, encouraging their use. Wildlife fencing along the corridor will guide animals toward the crossing, ensuring safe passage.

The overpass is expected to reduce wildlife-vehicle collisions by up to 90%, a critical outcome for a region where such incidents are frequent. By linking fragmented habitats, it will support the long-term survival of diverse species, from coyotes to mountain lions, all while keeping commuters safe. 

As of a July update, Colorado officials are indicating that the Greenland Wildlife Overpass is approximately 50% complete, entering its third of four construction phases. The final phase is slated to begin in September, and remarkably remains under budget. Construction has involved daytime and nighttime lane closures and reduced speeds on I-25, which will continue through 2025, but CDOT has committed to continue to work to minimize disruptions.

The overpass is part of a broader wildlife crossing system along the I-25 South Gap, which includes underpasses and 28 miles of deer fencing. Together, these measures address one of Colorado’s most pressing conservation challenges while accommodating the region’s growing transportation demands.

The Greenland Wildlife Overpass stands out not only for its size but also for its ambition. While it surpasses California’s Wallis Annenberg Wildlife Crossing (spanning 10 lanes) in width, it is shorter than the half-mile-long Zanderij Crailoo Nature Bridge in the Netherlands. Its $15 million price tag is notably lower than similar projects, such as a proposed $28-$30 million initiative for crossings along Wyoming’s Highway 26/287. 

As the Greenland Wildlife Overpass nears completion, it promises to be a landmark achievement in conservation and transportation. With more elk than any other state in the country and healthy mule deer herds, there should be no issue getting some use out of this big, beautiful endeavor.