On March 15, 1968, construction started on the north tunnel of
the Eisenhower/Johnson Memorial Tunnel on Interstate 70 in
Colorado, some 60 miles west of Denver.

Located at an elevation of more than 11,000 feet, the project was
an engineering marvel and became the world’s highest vehicular
tunnel when it was completed in 1979. Four months after opening,
one million vehicles had passed through the tunnel; today, some
10 million vehicles drive through it each year.