Colorado’s mountains and weather long constrained travel across the Continental Divide, and after an abandoned pioneer tunnel near Loveland Pass in 1941–1943, changing road standards, agricultural needs on the Western Slope, tourism growth, and federal funding under the 1956 Interstate Highway Act led to selection of the Straight Creek route for a major all-weather crossing. The westbound bore, later named the Eisenhower Memorial Tunnel for Dwight D. Eisenhower, opened on March 8, 1973, saving motorists 9.1 miles over Loveland Pass and linking east and west Colorado more reliably year-round. Because one tunnel carrying traffic both ways was not a long-term solution, excavation of the eastbound bore began in 1975, and the Johnson Tunnel, named for Governor and U.S. Senator Edwin C. Johnson, was completed and dedicated on December 21, 1979. Construction at high altitude faced bad rock, a moving mountain along the Loveland Fault, short seasons, and reduced worker and equipment efficiency, prompting engineers including Charles Shumate, R. C. Hopper, and Phillip McOllough to adopt methods such as multiple small drifts filled with concrete to prevent cave-ins. Janet Bonnema’s hiring as a tunnel engineer in 1970 and her underground work after a 1972 equal-rights amendment marked a change in the Department of Highways’ workplace culture despite a brief worker walkout. Built over 13 years at a cost of $220 million including ventilation buildings and approaches, the Eisenhower-Johnson Memorial Tunnels stand at 11,158 feet as the highest point on the Interstate system and have carried hundreds of millions of vehicles on a route maintained around the clock.