In 1944 the Federal Highway Act authorized a national highway network to connect major urban areas.  In 1956 the federal government began providing 90 percent of the funding for upgrading the interstate system which resulted in a boom of highway building in the 1960s and 1970s. A major project was the building of I-70 over the Continental Divide west of Denver. This mountain barrier had always been an obstacle to travelers attempting to go through the mountains. Constructing any sort of passage through the peaks, whether it was an Indian trail, railroad tracks or an early road was difficult because of the steep grades, heavy snowfall,  mud and rocky mountainsides. Berthoud, Loveland, Vail, and Rabbit Ears passes were frequently inaccessible during the winter months, thus isolating the Western Slope. A safe, all-weather route was needed to provide a necessary link, including a tunnel dug through the highest elevations. After much research and debate, a route that would follow U.S. 6 to Frisco, Wheeler Junction and Vail Pass was decided upon and the pilot bore under the Continental Divide was begun in October of 1963. The Eisenhower Memorial Tunnel opened in 1973 while a second bore, the Johnson Tunnel, was completed in 1979. This photo shows the tunnel on March 16, 1973.