With some hard work between Native American tribes, Montana highway engineers, and Montana State University, wildlife on the Flathead Indian Reservation have safe passage to cross US Highway 93 on grass overpasses.

Audio Slide Show: Right of Way from Orion Magazine on Vimeo.

There are 41 wildlife-friendly overpasses along a 56-mile stretch of Highway 93. The overpasses were built after the Confederated Salish and Kootenai Tribes asked the Montana Department of Transportation to mitigate the impact of Highway 93's expansion on the reservation's wildlife. Between 1998 and 2010, thousands of animals including four grizzly bears, have been killed on this stretch of road.

One estimate says between one and two million animals are killed by cars each year in the US -- or about one every 26 seconds. Those numbers, moreover, only count reported collisions, which rarely include the deaths of small animals who run over without the driver even noticing. According to the Federal Highway Administration, cars are a serious threat to 21 endangered or threatened species, including bighorn sheep, red wolves, and desert tortoises.

Highway overpasses for animals are a fairly expensive solution. Cheaper options include reduced speed limit zones and roadside animal detection systems, which warn drivers of oncoming animals with flashing lights.