The Zion-Mount Carmel Tunnel (and the Zion-Mount Carmel Highway) provides direct access for travel between Bryce Canyon, Grand Canyon, and Zion National Parks.
Construction of the 1.1 mile Zion-Mount Carmel Tunnel began in the late 1920s and was completed in 1930. At the time that the tunnel was dedicated, on July 4, 1930, it was the longest tunnel of its type in the United States.
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A century ago, the United States wanted to make its national parks more accessible—not an easy proposition back then for the parks in remote areas. To allow for direct access to Bryce Canyon and the Grand Canyon from Zion National Park, workers built a 24-mile-long highway through Zion, which includes the 1.1 mile Zion-Mount Carmel Tunnel, opened in July 1930 as the longest tunnel of its type in the country at the time.
It wasn't easy. Working in relatively soft sandstone, workers decided to create windows in the sides of the cliffs to remove the stone as they went. The softness also has required concrete reinforcement and a full-time electronic monitoring system that would alert park officials to any shift in the stone. Nowadays the tunnel is too small to handle two-way traffic of our oversized modern vehicles, so the typically one-way tunnel is managed during heavy tourist times, sometimes requiring long waits to enter.
source:https://www.popularmechanics.com/
edited by olivia