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Salt Creek Half Viaducts
PURPOSE AND NEED FOR THE ACTION
Salt Creek Half Viaducts
The purpose of the proposed action is to rehabilitate the existing Salt Creek Half Viaducts, or Bridges (considered “bridges” on a structural level) to allow them to carry legal loads and meet current safety and operational standards while maintaining mobility along this designated Freight Route.
 
The Salt Creek Half Viaducts are all either structurally deficient or are in need of barrier improvements to meet current safety standards.  The proposed action is needed to maintain this route as a viable Freight Route and alternative to Interstate 5 and to improve safety for the traveling public.
 
In essence, a modern solution for the same challenge the roadway designers faced in laying out this section in 1933: maximize the scenic qualities while maintaining a safe passage.
 

WHAT IS A HALF VIADUCT?
Half viaducts are elevated roadways supported by piers that are built into the side of the hill to accommodate the roadbed and cling to a severe slope.  Considered half viaducts, they provided lateral structure for only the half of the road that was not cut into the side of the mountain.  The use of rock walls and viaducts were used so to “not to scar the hillsides more than is absolutely necessary” as the road cut through the Willamette National Forest, according to the Chief Locating Engineer (July 15, 1933). 
 

DESCRIPTION OF ACTION
2006 Salt Creek Half Viaduct
The Salt Creek Half Viaduct Repair Project provides necessary repairs to the exterior concrete girders on all four half viaducts, adjacent to the Salt Creek Falls on the Willamette Highway (OR 58) near Willamette Pass, Lane County, Oregon (Appendix D,  page 1).  These structures have been identified as structurally deficient, and are in need of repair or replacement.  The repair alternative was chosen over the replacement due to the need for the use of these structures as an Interstate 5 detour during the shared construction period.  The purpose of the project is to rehabilitate these structures to carry legal loads while maintaining mobility through the corridor.  This rehabilitation consists of three separate but connected elements.  First, the deteriorated girders on the structures are in need of repair.  Second, the rehabilitation will correct the safety deficiency of the existing unreinforced masonry railing on and between these viaducts by providing a guardrail retrofit that meets current ODOT impact standards.  Third, the rehabilitation will provide for adequate live load capacity by removing the maximum amount of dead load from these structures possible while maintaining an acceptable vertical profile.  Currently, these structures have as much as 28 inches of material over the bridge deck and to provide adequate live load capacity this will be reduced to a maximum of 16 inches.

 
Please see the Project Document below for the complete adn formal project review.

PROJECT DOCUMENTS
Originally posted January 5, 2007, FHWA comments incorporated February 2, 2007
 
Draft Section 4(f) Evaluation Report
Appendix A- Determination of Eligibility for the National Register, Highway Tunnels in Oregon
Appendix B- Oregon Inventory of Historic Properties
Appendix C- Memorandum of Aggreement
Appendix D- Site Location Maps
Appendix E- Existing Condition Photographs
Appendix F- Drawings
 
Project Information Paper

HISTORY
1940 Salt Creek Half Viaduct
The Salt Creek Half Viaducts are significant and contributing to the potentially eligible Salt Creek Tunnel historic district under Criterion C as embodying distinctive characteristics of highway viaduct construction before World War II using the Bureau of Public Roads (now the Federal Highway Administration) design standards.  Connected with the Salt Creek Tunnel, it is part of one of the only twelve highway tunnel systems built in Oregon between 1914 and 1941, and one of seven in Oregon that feature the National Parks Service rustic-style masonry built between 1937 and 1941.  This district is also a fine example of a Bureau of Public Roads and Oregon State Highway Department (now ODOT) cooperative effort that combined the dual needs of providing an important transportation route through the Cascade Mountains with a recreational and scenic drive.  At the time, Willamette Highway was roundly thought to be the last major highway the state would need, and therefore a crowning achievement in design and function, as indicated at the road’s opening in a speech by Governor Sprague (July 30, 1940).
 
The concrete half viaducts were built in 1939-1940 and are elevated roadways supported by piers that are built into the side of the hill to accommodate the 30 ft. roadbed.  Considered half viaducts, they provided lateral structure for only the half of the road that was not cut into the side of the mountain.  Like the tunnel, the half viaducts were built from plans provided by the U.S. Bureau of Public Roads.  The parapeted masonry guard rails are located along the outside edge of the road on the half viaducts east of the tunnel.
 
The use of rock walls and viaducts were used so to “not to scar the hillsides more than is absolutely necessary” as the road cut through the Willamette National Forest, according to the Chief Locating Engineer (July 15, 1933).  Half viaducts were implemented to both cling to a severe slope on both sides of the tunnel while limiting the visual impacts of an engineered bridge on nearby trails in the National Forest.  The tunnel portal ring stones were trucked down from Rocky Butte near Portland, while local stone, which did not meet the structural needs for the portal ring stones, could serve for the construction of the masonry guard rails and the remainder of the masonry portals.
 
Previous work replacing the Salt Creek Tunnel lighting led to a successful determination of eligibility of the Salt Creek Tunnel Historic District for the National Register of Historic Places by the Oregon State Historic Preservation Office (SHPO).  The SHPO letter of concurrence was signed on January 21, 2000, agreeing that the district would include “the tunnel, the four associated half viaducts, the rock walls near the portals, the masonry guard rail on the three east end half viaducts, and the power house under the west viaduct.
 
Comparing the portals and associated features for Oregon’s seen tunnels built between 1937 and 1941; all show a striking resemblance however none are identical, reflecting the conditions and needs of each particular site.  In the last half of the 1930’s, the federal government contributed to and oversaw two-dozen highway tunnel projects, mostly in the West.  Of those inside our National Parks, they include three tunnels in Yosemite National Park, two tunnels in Mount Rainier National Park, and two of the Zion Tunnel in Zion National Park.  Despite their location inside a National Park, only a few included rustic-style portals and masonry which the NPS made famous.  Most of the Western tunnels received smooth-faced concrete portals to purport stability among jagged rock.  As such, with seven tunnels with NPS rustic-style masonry, Oregon maintains one of the best collections of 1930s/1940s NPS rustic-style highway tunnels in the country.