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/