The completed Pretty Rocks steel truss bridge spanning Polychrome Pass in Denali National Park

Flagship Project

Pretty RocksBridge

Denali National Park & Preserve • Alaska

Fabrication for one of America’s most challenging bridge projects.

Polychrome Pass • Denali Park Road, Mile 45.4

475 FT: Bridge Length
50 FT: Bridge Height
24 FT: Bridge Width
1.65M LB: Steel Launched

The Challenge

A road severed by
a moving mountain.

At Mile 45.4 of the Denali Park Road, the active Pretty Rocks Landslide cut the only route through Polychrome Pass. Warming permafrost had accelerated the slide to more than a foot of movement per day, faster than crews could rebuild the grade.

The answer was a 475-foot steel truss bridge, engineered to span unstable, ice-rich terrain in one of the most remote construction environments in the United States. Without it, 47 miles of park road and the attractions beyond would stay closed to vehicles.

Location: Denali National Park & Preserve, Alaska
Crossing: Pretty Rocks Landslide, Polychrome Pass
Structure: 475 ft modified Warren steel truss
Method: Incremental launch
Deck: SPS® sandwich plate system
Scope: Structural steel fabrication

Bridge launch across the Pretty Rocks Landslide, valley view — Bridge launch across the active Pretty Rocks Landslide

Steel truss cantilevered over the active slide at Polychrome Pass — Bridge launch across the active Pretty Rocks Landslide

Engineering the Crossing

Assembled on one side.Launched across the void.

The bridge was built up on the east side and launched across the active slide. A purpose-built temporary launch truss ran inside the permanent truss, letting the structure advance toward the receiving tower before it was jacked down into final position. The operation demanded tight tolerances, custom roller locations and careful sequencing.

Truss erection with crew working on fabricated steel members — Truss erection + bridge interior

Interior view down the permanent bridge truss — Truss erection + bridge interior

SPS® Deck Fabrication

Deck panels, shop-built to spec.

Actual project deck panels during fabrication and preparation. The SPS® sandwich plate system bonds two steel face plates around a solid polymer core, producing a stiff, durable deck that carries less weight than a conventional concrete slab. On a launched span in a remote, load-sensitive site, that weight saving matters.