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Isthmus Slough Bridge

Photo taken by Historic American Engineering Record

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Overview: Through truss bridge over Isthmus Slough on FAS A-396
Location: Coos County, Oregon
Status: Replaced by a Concrete Box Girder Bridge in 2004
History: Built 1955, Replaced 2004
Builder: - P. Mervyn Stephenson (Bridge Engineer)
Design: The Isthmus Slough Bridge is significant as a good example of the bascule bridge type. This bridge is unique within the Oregon context at it is the only known bascule structure that utilizes a block and tackle lifting mechanism, as opposed to the more common motorized lifting mechanism. The lack of motorized technology distinguishes this structure within Oregon's context of moveable bridges. The Isthmus Slough Bridge is also significant as a late example of the bascule type within Oregon, as it is only one of three bascule spans built after WWII.
(HAER OR-144 - Isthmus Slough Bridge)
Dimensions: Length of largest span: 85.0 ft.
Total length: 686.1 ft.
Deck width: 24.0 ft.
Vertical clearance above deck: 14.1 ft.
Recognition: Eligible for the National Register of Historic Places
Approximate latitude, longitude: +43.30083, -124.20861 (decimal degrees)
43°18'03" N, 124°12'31" W (degrees°minutes'seconds")
Approximate UTM coordinates: 10/401969/4794931 (zone/easting/northing)
USGS topographic map: Coos Bay
Inventory numbers: OR 02300A (Oregon Dept. of Transportation structure number)
BH 29928 (Bridgehunter.com ID)
Inspection (as of 08/2005): Deck condition rating: Good (7 out of 9)
Superstructure condition rating: Serious (3 out of 9)
Substructure condition rating: Poor (4 out of 9)
Appraisal: Structurally deficient
Sufficiency rating: 13.5 (out of 100)
Average daily traffic (as of 2004): 1,986

Isthmus Slough Bridge

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