+47.64317, -122.34719
47°38'35" N, 122°20'50" W


Source: National Bridge Inventory. Information not verified; use at your own risk.
Name:SR 99 over LAKE UNION
Structure number:0001447A0000000
Location:7.7 N JCT SR 509
Purpose:Carries highway and pedestrian walkway over highway, waterway, and railroad
Route classification:Principal Arterial - Other Freeways or Expressways (Urban) [12]
Length of largest span:799.9 ft. [243.8 m]
Total length:2955.2 ft. [900.7 m]
Roadway width between curbs:56.4 ft. [17.2 m]
Deck width edge-to-edge:69.6 ft. [21.2 m]
Vertical clearance below bridge:134.5 ft. [41.0 m]
Owner:State Highway Agency [01]
Year built:1931
Historic significance:Bridge is on the National Register of Historic Places [1]
Design load:M 18 / H 20 [4]
Number of main spans:8
Main spans material:Steel [3]
Main spans design:Truss - Deck [09]
Deck type:Concrete Cast-in-Place [1]
Wearing surface:Bituminous [6]

Latest Available Inspection: August 2017

Good/Fair/Poor Condition:Fair
Status:Open, no restriction [A]
Average daily traffic:58,319 [as of 2012]
Truck traffic:3% of total traffic
Deck condition:Satisfactory [6 out of 9]
Superstructure condition:Fair [5 out of 9]
Substructure condition:Satisfactory [6 out of 9]
Structural appraisal:Somewhat better than minimum adequacy to tolerate being left in place as is [5]
Deck geometry appraisal:Basically intolerable requiring high priority of replacement [2]
Underclearances appraisal:Somewhat better than minimum adequacy to tolerate being left in place as is [5]
Water adequacy appraisal:Equal to present desirable criteria [8]
Roadway alignment appraisal:Equal to present desirable criteria [8]
Channel protection:Banks are protected or well vegetated. River control devices such as spur dikes and embankment protection are not required or are in a stable condition. [8]
Pier/abutment protection:Navigation protection not required [1]
Scour condition:Bridge foundations determined to be stable for the assessed or calculated scour condition. [8]
Sufficiency rating:46.9
Recommended work:Bridge rehabilitation because of general structure deterioration or inadequate strength. [35]
Estimated cost of work:$69,738,000

Previous Inspections

DateConditionDeckSuperstructureSubstructureADTSuff. Rating
August 2017FairSatisfactoryFairSatisfactory5831946.9
August 2015FairSatisfactoryFairSatisfactory5831946.5
August 2013FairSatisfactoryFairSatisfactory5831946.5
August 2011FairSatisfactoryFairSatisfactory6946344.4
December 2009FairSatisfactorySatisfactoryFair7108544.1
June 2007FairSatisfactorySatisfactorySatisfactory7383655.2
May 2005FairSatisfactorySatisfactorySatisfactory7383653.2
July 2003FairSatisfactorySatisfactorySatisfactory7383653.2
March 2001FairSatisfactorySatisfactorySatisfactory7383653.2
June 1999FairSatisfactorySatisfactorySatisfactory7383653.2
May 1997FairSatisfactorySatisfactorySatisfactory7383659.3
May 1995PoorSatisfactoryPoorSatisfactory7383627.9
June 1993PoorSatisfactoryPoorSatisfactory5936329.3
January 1992PoorFairPoorSatisfactory5936327.8

Element Data

Source: National Bridge Elements dataset, 2019 edition. This feature is experimental.
Reinforced Concrete Girder/Beamlinear ft.1,6821,6683110
Steel Stringerlinear ft.35,92135,8690520
Steel Protective Coatingsq. ft.427,40182,0610341,9213,419
Reinforced Concrete Stringerlinear ft.2,5232,521020
Reinforced Concrete Decksq. ft.166,957166,8940063
Wearing Surfacessq. ft.166,9570165,285721,600
Steel Trusslinear ft.4,2222,697251,5000
Steel Protective Coatingsq. ft.502,34996,4510401,8794,019
Steel Floor Beamlinear ft.5,9005,8680320
Steel Protective Coatingsq. ft.70,20013,478056,160562
Reinforced Concrete Floor Beamlinear ft.3,0003,000000
Steel Pin or Pin & Hangar Assemblyeach28180010
Steel Gusset Plateeach4383990390
Steel Columneach44000
Steel Protective Coatingsq. ft.4790380
Reinforced Concrete Columneach38215120
Reinforced Concrete Abutmentlinear ft.139139000
Reinforced Concrete Pileeach22000
Reinforced Concrete Pier Caplinear ft.3503380120
Strip Seal Jointlinear ft.171017100
Open Jointlinear ft.4,3320004,332
Assembly without Seal Jointlinear ft.684040322556
Movable Bearingeach22000
Fixed Bearingeach106040
Other Bearingeach1414000
Bridge Rail
Steel or Aluminum Bridge Raillinear ft.5,9105,77401360
Reinforced Concrete Bridge Raillinear ft.5,9105,8940160