Windward Viaducts, Road bridge in Oahu, United States.

The Windward Viaducts are twin concrete bridges running parallel to each other across the Koolau Range for several miles, carrying four lanes of Interstate H-3 traffic. These structures span across mountainous terrain to link Windward Oahu with central parts of the island.

Plans for a third interstate on Oʻahu date to the early 1960s; the National Environmental Policy Act of 1970 and local opposition pushed construction to the late 1980s. The joint venture SCI Engineers & Constructors and E. E. Black built the viaducts from 1990 to 1993 for 136 million US dollars. Interstate H-3, including the viaducts and the 1.5 km Tetsuo Harano Tunnel, opened in 1997.

The name Windward Viaducts follows Hawaiian usage: the windward side is the northeast coast of Oʻahu, exposed to the trade winds, as opposed to the leeward side where the North Halawa Viaducts stand. The H-3 crosses the Koʻolau Range between these two sides, and the paired viaducts take their name from the windward approach to the Tetsuo Harano Tunnel.

The viaducts carry daily traffic between Windward Oahu and the central areas, accessible via Interstate H-3. Drivers can expect typical highway conditions, though congestion may occur during rush hours.

The structure is made from precast cell box segments stacked to different heights, assembled like giant building blocks. This segmented construction method allowed faster assembly and reduced disruption during the mountain crossing project.