Glenwood Canyon became a critical link in the nation’s ground transportation network with the completion of the Denver & Rio Grande Railroad in 1887, followed by Taylor State Road, a continuous wagon road between Denver and Grand Junction that opened to automobile traffic in 1902, and later improvements after it was renamed U.S. Highway 6 and 24 in 1936. After President Dwight D. Eisenhower signed the National Highway Bill in 1960 authorizing construction of Interstate 70, Glenwood Canyon was proposed as part of the transcontinental route, but it did not officially become a link in the I-70 corridor until 1975. Planning, design, and construction then took nearly twenty years and involved an unusually lengthy, intense, and public process. Designers used artists' renderings, sophisticated computer simulations, and actual models to depict the finished highway realistically, walked every foot of the canyon many times, and adjusted the road's location by inches to save trees or avoid blasting cliff faces. Because of the canyon’s unique terrain and environmental constraints, builders used special techniques and equipment, including a red and white steel gantry that allowed the two longest bridges to be built without disturbing the ground below, while much of the equipment was adapted for tasks for which it had not been designed. Highway planners aimed to create a divided, four-lane highway that would complement rather than conflict with the canyon’s natural magnificence.