PACIFICA, Calif. (AP) — Two slick new mile-long tunnels are undergoing final safety tests this month, poised to divert motorists away from an ocean cliff-hanging roadway dubbed Devil’s Slide south of San Francisco to a smooth, Alpine-like passageway unlike any in the U.S. today.

The $439 million project, paid with federal emergency funds, features massive exhaust fans, carbon monoxide sensors and a pair of 1,000-foot bridges soaring 125 feet above a grassy horse ranch. A series of 10 fireproof shelters are staggered between the double bores, and remote cameras dangle from the ceiling, monitored by an around-the-clock safety staff of 15.