Polychrome Area Plan

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Note: This page describes the planning effort for a long-term solution for the Denali Park Road in the Polychrome area. The Planning, Environment, and Public Comment (PEPC) website has details about upcoming public meetings and opportunities to submit comments as part of the compliance process for the proposed project.

Denali National Park and Preserve is proposing improvements to the Park Road in the Polychrome Area to address several geologic hazards, including the Pretty Rocks Landslide, that threaten public safety and infrastructure. The project will focus on engineered solutions along approximately two miles of the Park Road (mile 44-46).

Read more about the science and monitoring of the Pretty Rocks Landslide and other geologic hazards.

 

NPS road maintenance staff made an extraordinary effort in Spring 2021 to repair the road at Pretty Rocks

NPS Photo

Planning Process

The collaboration between the National Park Service (NPS) and Federal Highways Administration (FHWA) to develop a long-term solution for the Park Road in the Polychrome Area began in the winter of 2017-2018. FHWA brainstormed several conceptual ideas, ruled them out one-by-one through preliminary evaluation, and narrowed it down to three alternatives for further consideration: bridging the landslide, removing the upper landslide, and detouring around the landslide.

In 2019, FHWA conducted geotechnical investigations at Pretty Rocks and confirmed that the rock mass strength of the material at the east and west abutments was sufficient to support a bridge so it was retained as a viable alternative. Further analysis determined that removal of the upper landslide would cause the slope to become unstable again in 10-15 years due to the continuous exposure of the weak ash layer, so it was eliminated as a long-term solution.

In 2020, NPS and FHWA partnered to conduct an Expert-Based Risk Assessment (EBRA) and a value analysis (VA) that evaluated the remaining alternatives, including north and south re-routes and a mainline option that would retain the existing road alignment. NPS identified four criteria to use for evaluating the options: feasibility of construction, continuity of access during and after construction, resiliency / life cycle, and how it supports the Denali NP mission statement.

 

FHWA and NPS evaluated several alternatives and decided to move forward with the mainline (option 1)

FHWA Polychrome Pass Project Development Plan

Based on the outcomes of these expert panels, FHWA recommended the mainline option, which included building a bridge across the Pretty Rocks Landslide. NPS agreed that the iconic viewpoints, historical character, and known geotechnical challenges of the existing alignment (the mainline option) far outweighed the benefits of placing a new road in the Wilderness area that would take 11-14 years to construct. FHWA moved forward with the design for the bridge and the additional engineering solutions for the mainline option in Fall 2020.

In 2021, additional geotechnical investigation was done to inform the design of the bridge as well as the preliminary design of the retaining wall at Bear Cave slump. FHWA provided NPS with preliminary (30%) design plans for a Pretty Rocks bridge. The next step in the planning process is to complete the required compliance, which will assess the potential environmental impacts of the proposed project.

 

FHWA engineers visited the site of the proposed Pretty Rocks bridge in August 2021

AECOM / Jon Isaacs

Project Overview

The proposed project to address several geologic hazards along approximately two miles of the Denali Park Road (mile 44-46) is referred to as the “Polychrome Area Improvements” project and has been separated into two phases:

Phase I

• Excavation of the uphill slope to the east and west of the bridge to accommodate construction activities and traffic. Some of the excavated material would be stored or used to temporarily maintain the existing road across the landslide, and the rest would be placed below the road.
• Slight realignment of the road on the west side of the bridge to allow for a proper turning radius for buses and other vehicles getting on and off the bridge
• Installation of a retaining wall east of the landslide, on the uphill slope.
• Construction of a 400-foot launchable modular steel truss bridge to span the Pretty Rocks landslide. A temporary platform would be installed on the east side to extend the staging area during bridge construction.
• Rock scaling, rock reinforcement with bolts, and creation of a rockfall ditch to mitigate rockfall hazards.

Phase II

• Construction of a retaining wall on south side of the road and roadway shift at Bear Cave slump
• Rock scaling, rock reinforcement with bolts, creation of rockfall ditches, and laying back uphill slopes at several additional sites to mitigate rockfall hazards.

The current federal budget proposal allocates $53 million in funding for the continued design and implementation of Phase I, which includes a bridge at Pretty Rocks. Phase I would require five months of excavation plus three months of bridge construction and would take approximately two years to complete.

Traffic would not be allowed through the area during much of Phase I, particularly during excavation. However, traffic may be allowed through the area during some periods of the bridge construction, likely on a limited schedule. The project is scheduled to begin in 2023 but given the recent road closure and the anticipated challenge to repair and maintain the road through Pretty Rocks in 2022, NPS and FHWA are pursuing contracting and funding options to be able to begin sooner.

An additional $65 million would be required to complete Phase II and it would be implemented at a later date.

 

Duration:

1 minute, 58 seconds

Take a brief tour of the bridge designed for Polychrome, to span the landslide at Pretty Rocks. No audio.

 

NEPA and NHPA Compliance

The National Environmental Policy Act (NEPA) mandates an environmental assessment (EA) of any proposed federal action that has the potential to “significantly affect the quality of the human environment." Section 106 of the National Historic Preservation Act (NHPA) requires that federal agencies identify and assess the effects its actions may have on historic properties and consider public views and concerns about historic preservation issues when making final project decisions.

Denali National Park and Preserve has contracted an environmental consulting firm (AECOM) to prepare the EA for the proposed Polychrome Area Improvements project. Environmental and cultural compliance will be formally initiated in October 2021 and will be completed by March 2022.

The following steps will be followed for the compliance process:

• Step 1. Conduct public / civic engagement (Oct ‘21)
• Step 2. Identify environmental impacts and select preferred alternative (Nov ‘21)
• Step 3. Develop an agreement document with the State Historic Preservation Office (Nov ’21)
• Step 4. Prepare draft plan/environmental document (Dec ‘21)
• Step 5. Public review of draft plan/environmental document (Jan ‘22)
• Step 6. Analysis of public comment (Feb ‘22)
• Step 7. Prepare final plan/decision document (Feb ‘22)
• Step 8. Release final plan/decision document to the public (March ‘22)

As part of the civic engagement period, the NPS will host two virtual public meetings in October to provide information and answer questions. Both meetings will have the same schedule and format, consisting of a presentation and question and answer session. The goal of these meetings is to identify and document specific concerns, issues, and potential impacts for consideration during the development of the Environmental Assessment. Comments on the project can be submitted from Sept 29th-Oct 29^th and the NHPA Assessment of Effects determination will be available for public review for 30 days, beginning in mid-October.

Following the October public meetings, an Environmental Assessment will analyze the no action alternative and action alternative(s). Issue topics considered will include cultural resources, wildlife, wetlands / vegetation, noise / soundscape, wilderness, visitor use and experience, socioeconomics, visual / viewshed, and geologic resources. There will be additional opportunity for the public participation following the publication of the draft Environmental Assessment in January 2022.

 

How Can I Get Involved?

Check the NPS public comment website for updates on public meetings and documents available for review and comment.

If you have questions, please email us.