March 15, 1968 – Construction begins on highest tunnel in the US

At the time of its completion the Eisenhower–Johnson Memorial Tunnel, about 60 miles west of Denver, Colorado, was the world’s highest tunnel with a maximum elevation of 11,158 ft (3,401 m). Construction of the 1.693 mile (2.72 km) tunnel, a part of Interstate 70, broke ground on this day in 1968, starting with the westbound bore named after President Dwight D. Eisenhower.

The eastbound bore, named for Edwin C. Johnson, a Colorado governor and U.S. Senator who lobbied for an Interstate Highway to be built through Colorado, was initiated in August of 1975, about a year and a half after the first bore was opened to traffic. The tunnel remains the highest tunnel in the United States but higher tunnels have since been constructed. The world’s highest tunnel to date, completed in 2016, sits at an astonishing 20236.22 feet (6,168 meters) above sea level and shortens the drive between Chengdu, capital of Sichuan province, China, to Nagqu, Tibet by two hours.