 With the Eisenhower Tunnel finished , the last remaining obstacle for I @-@ 70 to be an interstate commercial artery was the two lane , non @-@ freeway portion in Glenwood Canyon . Construction had started on this section in the 1960s with a small section opening to traffic in 1966 . The remainder was stopped due to environmentalist protests that caused a 30 @-@ year controversy . The original design was criticized as " the epitome of environmental insensitivity " . Engineers scrapped the original plans and started work on a new design that would minimize additional environmental impacts . A new design was underway by 1971 , which was approved in 1975 ; however , environmental groups filed lawsuits to stop construction , and the controversy continued even when construction finally resumed in 1981 . The final design included 40 bridges and viaducts , three additional tunnel bores ( two were completed before construction was stopped in the 1960s ) and 15 miles ( 24 km ) of retaining walls for a stretch of freeway 12 miles ( 19 km ) long . The project was further complicated by the need to build the four @-@ lane freeway without disturbing the operations of the railroad . This required using special and coordinated blasting techniques . Engineers designed two separate tracks for the highway , one elevated above the other , to minimize the footprint in the canyon . The final design was praised for its environmental sensitivity . A Denver architect who helped design the freeway proclaimed , " Most of the people in western Colorado see it as having preserved the canyon . " He further stated , " I think pieces of the highway elevate to the standard of public art . " A portion of the project included shoring up the banks of the Colorado River to repair damage and remove flow restrictions created in the initial construction of US 6 in the 1930s . 
