Wildlife overpasses are bridges built for animals, letting them cross highways safely while traffic flows underneath. Colorado’s Greenland overpass — North America’s largest — has cut wildlife-vehicle collisions by 91 per cent in nine months. Here’s how they work.

The idea is simple: roads slice through animal migration routes, forcing crossings that kill both animals and drivers. A crossing pairs a wide bridge or tunnel with long stretches of fencing that funnel animals toward it, so they don’t slip onto the road.

Design matters. Entrances are broad and gently sloped, and the surface is covered with soil and plants so it feels like the land itself, not a structure. Big animals like elk and pronghorn need wide, open sightlines to feel safe; smaller species prefer enclosed underpasses.

The payoff goes beyond fewer crashes. The Greenland bridge reconnected 39,000 acres of habitat, and pronghorn reached the west side of I-25 for the first time in decades. Elsewhere, studies show reductions of 80 per cent or more — proof that a bridge built for hooves can save lives on four wheels too.