The extra width is critical for wildlife because they have to perceive it as normal terrain, with dampened road noise, and it needs lots of ways to feel like you can sneak through otherwise no one would use it because they would feel too exposed.

[–] supersquirrel@sopuli.xyz 3 points 2 weeks ago* (last edited 2 weeks ago)

See this open access study Wildlife overpass structure size, distribution, effectiveness, and adherence to expert design recommendations.

We conclude that wide overpasses (~50 m) continue to present important, cost-effective solutions in decreasing the barrier effective of the road (especially when targeting width sensitive species and large assemblages of mammals) but encourage future studies to further explore the specific instances when multiple underpasses and narrower overpasses present more cost-effective solutions.

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