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.
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.
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.
Project OverviewThe 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:
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.
NEPA and NHPA ComplianceThe 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:
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.
Last updated: October 15, 2021