To protect the movement of wildlife impeded by busy roadways, a series of manmade overpasses and underpasses throughout the United States helps animals big and small safely get across the street, preventing collisions and saving lives. About 1,500 of these structures already have been built. Correspondent Conor Knighton looks at how they have protected genetic diversity in animal populations while also greatly reducing roadkill. He also visits the site of the Wallis Annenberg Wildlife Crossing near Los Angeles, which when complete will help cougars cross one of the busiest highways in the country.