The Wallis Annenberg Wildlife Crossing has a completion date: Dec. 2, announced at an Earth Day news conference held on the structure rising over a 10-lane stretch of the freeway. Cars whizzed by below.

That’s when the ribbon will be cut and mountain lions suffering from a lack of genetic diversity are expected to get their ticket out of the freeway-locked Santa Monica Mountains to seek mates elsewhere.

“This is a visionary project that was the impossible dream,” said Beth Pratt, California regional executive director with the National Wildlife Federation and the public face of the crossing. “This is something that’s captured the imagination of Angelenos, captured the imagination of the world.”