One million animals annually are killed on roads in the U.S., and this situation highlights the pressing need to engage engineering expertise to reconnect habitats. This need has been addressed in Colorado through the opening of the Greenland Wildlife Overpass, which has become the largest wildlife crossing bridge in North America, crossing Interstate 25 between Denver and Colorado Springs.
The overpass is more than just a symbol of consciousness about preserving the environment; rather, it is designed with utmost detail with the aim of preserving the passage of elks, mule deer, black bears, mountain lions, and other wild animals whose migratory routes through the region were halted by six fast-moving traffic lanes. With dimensions that include 200 feet wide and 209 feet long, spanning 41,800 square feet and put up at the cost of $15 million, the project connects 39,000 acres that were divided by the interstate. It is expected to lower wildlife and vehicle crashes by 90% by the state transportation department CDOT, which corresponds with figures that indicate wild animal and vehicle crashes can be reduced by as much as 97% when crossing points along with fencing are incorporated.
The Greenland overpass represents the completion of an 18-mile wildlife crossing network involving the use of underpasses and fencing. This was achieved at a critical 3.7-mile section of land where the movement of animals was at its peak. Engineers ensured the line of sight to the crossing was clear because animals rely greatly on the use of line of sight to navigate. A Colorado Parks and Wildlife official, Kara Van Hoose, observed, “Wildlife now can kind of go on a little bit of an adventure that they weren’t (able to) before.”
The solution incorporates the findings of a vast body of research in the field of transportation ecology, which has established the negative effects of habitat fragmentation, not only killing animals but causing the reduction of genetic diversity and the extinction of populations. Among larger mammals like elk and mountain lions, disconnected migration paths may reduce their territory to the point of non-viability, as in the heartbreaking case of the Los AngelesMountain Lion P-22, whose inaccessibility ended in a fatal encounter with a car.
On the engineering front, the animal overpasses have to be able to resist the forces of nature while supporting the environment as well. The one in Greenland employs concrete “arches” that hold up the weight of the earth and vegetation, and the presence of “drainage” ensures that the vegetation remains intact and the earth isn’t eroded away. Materials with life cycles of several decades, similar to those of highway bridges, have been used. The quick turnaround of the project in a year is the result of better modular construction methods and greater government and nonprofit coordination.
The economic argument is also strong. Vehicle-wildlife collisions result in between $8-11 billion a year in losses for the U.S. economy, sensitive to medical, repair, and lost productivity costs. It has also been observed that crossings are capable of self-recovery within two decades by reducing crashes. In Wyoming, an overpass/underpass structure for mule deer and pronghorns was likely to recoup investment of $12 million within 17 years.
However, such achievement comes as other giant projects are stretching the boundaries even further. For example, the Wallis Annenberg Wildlife Crossing, measuring 210 feet long and 174 feet wide, is being erected across the ten lanes of Highway 101, aiming at reconnecting the mountain lion sub-populations within the Santa Monica Mountains. Estimated costs for this project stand at $92 million, expected to be completed in 2026. It is set to be the largest wildlife crossing worldwide. The Greenland Overpass is also an example of how wildlife concerns can and should be incorporated into transport planning.
The Wildlife Crossing Pilot Program, supported through the Bipartisan Infrastructure Law, has already allocated $110 million to projects across the country. As CDOT Executive Director Shoshana Lew has observed, “The I-25 Greenland wildlife overpass is critical to the safety of both wildlife and motorists.” The importance of both road safety and habitat connectivity is an increasingly recognized joint objective. Through integrating ecological principles in civil engineering structures, examples like the Greenland Wildlife Overpass prove that green engineering is capable of yielding tangible results in terms of improved habitats not only within the animal kingdom but also within the human kingdom. These are not just bridges but are rather life-giving paths in the ecological framework of the continent.
