Solarpunk

I actually think the ecosystem benefit here will quickly payback even that large of an investment, an open air, safe feeling wildlife transit corridor for wildlife can easily be a keystone piece of architecture in maintaining a regional ecosystem and flow of nutrients/migration of animals. That isn't even bringing into the picture the MASSIVE cost savings that a reduction in wildlife-vehicle collisions inherently provides.

Benefits of crossings

The U.S. records more than 1 million wildlife–vehicle collisions each year, and that is probably an undercount because of unreported incidents.3 These crashes cost more than $10 billion annually in repairs, medical care, and lost productivity, and they cause about 200 deaths and 26,000 injuries annually.4 According to the Federal Highway Administration, wildlife crossings can deliver key benefits for drivers and wildlife, including:

Crash prevention: Wildlife crossings with fencing can cut large-mammal collisions by more than 80%—and up to 97% for certain species, including deer and elk—making them among the most effective ways to improve driver safety and wildlife connectivity.5

Cost savings: Each prevented wildlife–vehicle collision can save thousands of dollars—more than $19,000 per deer crash, $73,000 per elk, and $110,000 per moose—in vehicle, injury, and wildlife costs, making well-placed crossings a strong investment.6

Habitat connectivity: Roads, fences, and development break up landscapes and block wildlife migration, limiting animals’ access to food, water, and mates, which can cause population declines and reduce biodiversity by up to 75%.7

Communities throughout the country are investing in a range of wildlife crossings to improve public safety and protect vulnerable species. (See Figure 2.)

https://www.pew.org/en/research-and-analysis/fact-sheets/2026/01/wildlife-crossings-save-lives-cut-costs-and-protect-animals

Relevant article

https://y2y.net/blog/how-wildlife-crossings-revolutionized-conservation/

Another relevant study that looks interesting

https://pmc.ncbi.nlm.nih.gov/articles/PMC9753749/