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|Federal Highway Administration > Publications > Public Roads > Vol. 67 · No. 5 > A Tale of Two Canyons|
A Tale of Two Canyons
by Steve Moler
Colorado DOT applies lessons learned from the Glenwood project to a similar highway in the Snowmass valley, near the famed Aspen ski resort.
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".)
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 roadwaysone virtually on top of the otheralong 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.
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.
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 up-valley 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.
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.
"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."
During the drafting of the environmental impact statement, local county officials and the public wanted to evaluate transit options in addition to the four-lane highway. Five intermodal alternatives were developed, including a no-build option that served primarily as a baseline for evaluating the other alternatives. The preferred alternative provides for bus and high-occupancy vehicle lanes in some sections, bus park-and-ride facilities, a multimodal transfer station at the Buttermilk ski area, and a future commuter rail corridor that currently is under study.
Although Glenwood Canyon is almost four times longer, Snowmass Canyon arguably is more complicated, at least from a geotechnical standpoint. After more than 2 years of geotechnical studies and analysis, CDOT decided to construct more elaborate and complex soil-nail, tieback, and double-T walls using various types of post-tensioned ground anchors embedded in the bedrock to stabilize the hillsides. The department is building these earth retaining systemssome as long as 1,200 meters (4,000 feet)on both the up-valley and down-valley lanes. In all, the project includes 6 bridges and some 42 earth retaining systems.
"Anything that's considered state-of-the art from a geotechnical standpoint we're doing on this project," says CDOT project engineer Pete Mertes. "We have a great team of experts making this project a success."
The project's strategies to protect the environment rival and in some cases exceedthose employed in Glenwood Canyon. "CDOT has gone to great lengths to align the new highway based on established deer and elk migration routes," says Elsen.
Two of the project's six bridges are designed strictly as game crossings, allowing deer and elk to pass underneath the highway at ground level. An elaborate management system for storm water and a plan for controlling erosion are among the many measures CDOT is employing to help maintain the integrity and health of the Roaring Fork River and preserve its riparian zones.
"In Glenwood Canyon, the reconstruction required that we fix the banks of the Colorado River that were denuded or constructed hastily using rip-and-tear techniques," Elsen says. "But with Snowmass, we were able to avoid touching the Roaring Fork River."
Tree preservation is a major component of environmental preservation, as it was in Glenwood Canyon. CDOT designed much of the up-valley alignment to avoid as many stands of larger, more mature trees as possible. The space between the up-valley and down-valley lanes stands as an environmental island of untouched trees and vegetation. Disturbed areas will be replanted with native vegetation to return the canyon to its original condition.
With respect to recreation, CDOT took a page out of Glenwood Canyon's playbook, providing bicyclists with 2.5-meter (8-foot)-wide shoulders along the roadway for safe cycling. CDOT also created pedestrian access to the river at various points.
One advantage at Snowmass Canyon that CDOT did not enjoy in Glenwood was access to an alternate route to detour traffic during construction. In Glenwood, traffic had to be stopped for 30 minutes on average to allow construction crews to work because there was simply nowhere to divert traffic.
In Snowmass Canyon, during construction of the up-valley lanes (those at higher elevations), CDOT could divert one lane of traffic from S.H. 82 onto a county road located on the other side of the Roaring Fork River. Traffic going in the opposite direction could use one lane of
S.H. 82. This arrangement not only reduced the number and length of traffic delays but also gave construction crews more room and flexibility to work.
With the up-valley lanes now complete and handling all two-way traffic, the detour is no longer necessary. Construction of the down-valley lanes is in full swing. When CDOT completes the project as early as fall 2004, 1 year ahead of the original contract completion date, perhaps the improvements in Snowmass Canyon will lead motorists to consider changing the highway's nickname from "Killer 82" to "Son of Glenwood Canyon."
Steve Moler is the public affairs specialist at FHWA's Resource Center office in San Francisco.
Susanna Hughes Reck, the technology deployment specialist at FHWA's Lakewood, CO, satellite office of the Resource Center office in San Francisco, assisted with the sidebar on the video project for Snowmass Canyon.
For more information about the project in Snowmass Canyon, visit www.sh82.com/snowmasscanyon.html.itates Technology Transfer
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