Transportation Industry

A tale of two canyons: Colorado DOT applies lessons learned from the Glenwood project to a similar highway in the Snowmass valley, near the famed aspen ski resort

Public Roads, March-April, 2004 by Steve Moler

The Colorado Department of Transportation (CDOT) knows a thing or two about building highways through complex terrain. In 1992, CDOT completed an award-winning project that extended I-70 through Glenwood Canyon, finishing the last section of an interstate that stretches from Baltimore, MD, to Cove Fort, UT. The project later received the 1993 Outstanding Civil Engineering Achievement Award from the American Society of Civil Engineers and is considered one of the greatest highway engineering accomplishments in U.S. transportation history. (See "Glenwood Canyon 12 Years Later" on page 16.)

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Not one to rest on its laurels, shortly after finishing Glenwood Canyon the CDOT began planning a project in Snowmass Canyon 56 kilometers (35 miles) away. The Glenwood and Snowmass projects are remarkably similar. Both involve upgrading overburdened two-lane highways to four lanes through extremely narrow, ecologically sensitive canyons to improve safety and mobility while minimizing environmental impacts. "Both required exceptional planning, the latest in context-sensitive design, and construction ingenuity," says Ralph Trapani, the CDOT project manager on the Glenwood Canyon project, now a private consultant.

The project in Snowmass Canyon, which began in September 2000, applies the lessons that CDOT learned in Glenwood to upgrade a section of highway northwest of the ski resort town of Aspen. The $100 million project consists of widening 5.6 kilometers (3.5 miles) of State Highway (S.H.) 82 through Snowmass Canyon, a narrow valley carved by the Roaring Fork River. Like Glenwood Canyon, the Snowmass Canyon project involves building two roadways--one virtually on top of the other--along steep, geologically unstable slopes using a terraced system of retaining walls and bridges to minimize environmental impacts.

Saving the Hardest for Last

Snowmass Canyon represents the final section of roadway in a three-decade-long project to upgrade S.H. 82 from two to four lanes between Glenwood Springs and the Aspen area. As with Glenwood Canyon, which was the final segment of I-70 to be completed, the Snowmass Canyon section of the S.H. 82 upgrade was saved for last because it encompassed the route's most difficult environmental, engineering, and financial challenges.

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On October 14, 1992, the day CDOT cut the ribbon opening the Glenwood Canyon project, many of the project's planners, designers, and engineers turned their full attention to the difficult section of S.H. 82 between Basalt and Aspen, which contains the Snowmass Canyon segment. This 27-kilometer (17-mile) stretch of highway through some of the most scenic and majestic countryside in the United States had become one of Colorado's most dangerous two-lane highways for many of the same reasons that Glenwood Canyon attained a similar status a decade earlier. Undercapacity, high traffic volumes, sharp curves, narrow lanes and shoulder widths, lack of acceleration and deceleration lanes, and inadequate sight distances for passing eventually earned S.H. 82 the grim nickname "Killer 82."

By late 1992, CDOT had published a draft environmental impact statement for the section starting just east of Basalt and ending near Aspen. But CDOT and the Federal Highway Administration (FHWA) ultimately published a final environmental impact statement in October 1993 that covered the section from just east of Basalt to the Buttermilk ski area just outside Aspen. Upgrading the section inside the town of Aspen was considered in a subsequent environmental impact statement for the entrance to Aspen.

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Finding a Preferred Alternative

The primary debate over roadway alignments focused on whether to construct a one-way couplet for down-valley westbound traffic on the side of Roaring Fork River opposite the existing S.H. 82 through Snowmass Canyon. The new alignment would roughly parallel an existing railroad right-of-way. The upvalley eastbound traffic would use the old S.H. 82 roadway. Although this alternative would have saved millions in project costs, CDOT eventually rejected it because of the adverse impacts on wildlife and property owners along the proposed right-of-way.

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As the preferred alternative, CDOT and FHWA selected an alignment slightly higher up the canyon slopes from the existing highway, because it would have the least environmental and social impacts. The chosen alternative forced planners and designers to face the same predicament they had experienced with Glenwood Canyon: how to cram four lanes of roadway into an extremely narrow footprint, bordered by a river on one side and steep canyon slopes on another, without harming the environment.

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"The solution was challenging," says Joe Elsen, CDOT's manager for the Snowmass Canyon Project. "We were fortunate to be able to apply our knowledge and experience from Glenwood to the Snowmass Canyon site."