That’s a hypothetical that California’s Annenberg crossing, which should open to creaturely traffic in 2026, is prepared to test. Wildlife overpasses are generally funded with scarce public transportation dollars, and their landscaping tends to be relatively spartan. “Most put some dirt or gravel on top and call it a day,” Pratt said. By contrast, the $92 million Annenberg crossing, funded primarily through private donations, will be lushly surfaced in some 5000 native plants—including pollinator-friendly species like buckwheat, penstemon, and milkweed—collected as local seed and raised in an on-site nursery. Its soils will be inoculated with mycorrhizal fungi to ensure those plants flourish; wood and rocks will provide nesting sites for ants and bees. Even the sound-blocking earthen berms that shield wildlife from the freeway’s roar will be carpeted in a matrix of flowering plants that Robert Rock, the landscape architect responsible for designing the overpass’s surface, described as a “pollinator tapestry.”
“We want to create enough diversity in the habitat so that we invite insects to extend into this space,” Rock said. “All of these species are connected to everything that’s above and below them in the food pyramid.”
Though the Annenberg crossing might be the most thoroughly considered pollinator bridge, it isn’t the first. In 2017, the Clinton Keith Wildlife Crossing, an overpass in California’s Riverside County, opened to coyotes, mountain lions, roadrunners, and other critters. The crossing’s location was chosen, in part, to overlap with the range of the Quino checkerspot, an endangered butterfly whose wings are a vivid chessboard of white, black, and orange. Checkerspots have been described as “low-flying flutterers” more likely to bob through traffic than soar over it. “The overpass will get them to go higher than a road, to align them with the topography,” one biologist said not long after the passage opened.