 While designing the Eisenhower Tunnel , controversies erupted over how to build the portions over Vail Pass and Glenwood Canyon . The route of US 6 over Vail Pass has a distinctive " V " shape . Initially engineers thought they could shorten the route of I @-@ 70 by about 10 miles ( 16 km ) by tunneling from Gore Creek to South Willow Creek , an alternative known as the Red Buffalo Tunnel . This alternative sparked a nationwide controversy as it would require an easement across federally protected lands , through what is now called the Eagles Nest Wilderness . After the U.S. Secretary of Agriculture refused to grant the easement , the engineers agreed to follow the existing route across Vail Pass . The engineers added infrastructure to accommodate wildlife , and had significant portions of the viaducts constructed offsite and lifted in place to minimize the environmental footprint . The grade over Vail Pass reaches seven percent . 
