Interstate Highway 70 spans 2,100 miles across the United States, crossing the entire state of Colorado. The eastern end of the highway lies west of Baltimore, Maryland. From there it bisects the country until it reaches Cove Fort in Central Utah, where it merges into Interstate 15. In Colorado, I-70 crosses the Great Plains, runs through Denver, and crosses the Rocky Mountains, providing a direct route to many popular ski resorts and hiking trails. Because of its mountainous route, building I-70 through Colorado posed unique, often expensive, challenges to engineers and builders.
The Federal-Aid Highway Act of 1944 authorized the construction of Interstate 70 east of Denver, the first interstate highway to begin construction under the act. However, the initial route from Baltimore to Denver was deemed insufficient, as planners desired a more efficient connection between Southern California and the Northeast. Thus, the act was expanded in 1956, following the lobbying efforts of highway officials and road builders. The bill, passed under the title of “National Interstate and Defense Highways Act,” allocated $25 billion for enlarging and improving the highway system. The construction programs created by the 1956 act included the completion of the section of I-70 west of Denver into Central Utah, a monumental undertaking.
The construction of I-70 was mostly started and completed during the 1960s and 1970s, although the final connection through Glenwood Canyon was not finished until 1992. The 449.5 miles of highway were built in phases in an east-to-west direction. After building across the flat plains east of Denver, builders faced the challenge of the high Rocky Mountain peaks. Engineers designed a complex system of tunnels and bridges to traverse this difficult terrain. One particularly problematic area was the Continental Divide west of Denver. Engineers and construction crews had to cope with the high altitude, seemingly impassable mountain slopes, and harsh weather conditions. The solution was to build two tunnels—the Eisenhower Tunnel, which opened in 1973, and the Johnson Tunnel, which opened in 1979—both underneath Loveland Pass. These tunnels were named after President Dwight D. Eisenhower and Colorado governor Edwin C. Johnson, both of whom advocated for expanding the highway system and supported the 1956 highway act. The construction of the Eisenhower Tunnel cost twice the initial budget and ran two years over schedule, while construction of the Johnson Tunnel required $145 million and a work force of 800.
The final piece of I-70, the section passing through Glenwood Canyon, did not begin until 1981. The first project plan was approved in 1975, but environmentalists denounced the plan as ecologically damaging, and construction was delayed until 1981. To mitigate damage to the canyon, the 12.4-mile stretch of highway was designed to flow with the natural geography of the canyon, using an incredible array of forty bridges, many tunnels, bike paths, and cantilevered lanes to weave gently between the soaring cliffs. Completed in 1992, the freeway through Glenwood Canyon was widely heralded as an environmental and engineering success, although it took a whopping $490 million and eleven years to build.
Today, I-70 serves as a popular route for traveling across the Great Plains and through the mountains in Colorado, making it an important contributor to state and local economies. As a major east-west artery, the freeway is vitally important for interstate trade but is equally essential for drivers heading to the mountains for a variety of leisure activities. Its value to intrastate commerce is also noteworthy, as it accommodates trucks serving towns on the Western Slope and allows tourist dollars to filter into smaller mountain towns. Due to its economic and recreational importance, I-70 has become susceptible to heavy traffic congestion, especially west of Denver. The Colorado Department of Transportation (CDOT) has attempted to ease traffic by funding carpool programs to ski areas, purchasing additional snowplows, and widening problem areas, but citizens remain dissatisfied. The highway will continue to face traffic issues as development continues along the Front Range and as more drivers use I-70. Given the highway’s importance, CDOT will likely continue to fund projects aimed at improving safety and limiting congestion. Despite congestion issues, I-70 will continue to serve as the main gateway to the Rockies within Colorado as well as a major commercial artery connecting the eastern and western United States.