SR 520
over LAKE WASHINGTON
1.5 E JCT SR 513, King County, Washington
Condition
FairYear Built
2016
Daily Traffic
56,378
Length
764 ft
About This Bridge
SR 520 carries traffic over LAKE WASHINGTON in King County, Washington. Built in 2016, this structure is 10 years old, representing modern engineering and construction standards. The bridge features concrete construction with a other design, a combination chosen by engineers to meet the specific requirements of this crossing.
Approximately 56,378 vehicles cross this bridge daily, making it a high-traffic corridor critical to regional transportation. Bridges carrying this volume require enhanced inspection schedules and proactive maintenance programs. Commercial trucks account for 3% of all crossings. This proportion of commercial traffic is typical for this roadway classification and is factored into the bridge's design load ratings.
The bridge is currently rated in fair condition based on federal inspection criteria established by the Federal Highway Administration. The structure meets current safety standards for its designated use and load capacity. With a total length of 764 feet, this is a major span requiring specialized engineering expertise for inspection and maintenance. Longer bridges present unique challenges including thermal expansion, wind loads, and more complex structural analysis.
Concrete bridges offer excellent durability and relatively low maintenance requirements. They resist corrosion well but can develop cracking over time, particularly in regions with freeze-thaw cycles or heavy use of deicing chemicals. Regular inspection focuses on detecting cracks, spalling, and reinforcement corrosion.
Federal law requires that all highway bridges be inspected at least every 24 months by qualified inspectors following the National Bridge Inspection Standards (NBIS). Some bridges with known issues or unusual characteristics may be inspected more frequently. Inspection data is reported to the National Bridge Inventory, a database maintained by the Federal Highway Administration that tracks the condition of all public highway bridges in the United States. This bridge data is sourced from that federal database and reflects the most recent available inspection results.
Condition Ratings
Deck Condition
Good
Superstructure
Very Good
Substructure
Fair
Channel & Protection
Very Good
Lowest Rating
Determines condition category
NBI condition ratings range from 0 (failed) to 9 (excellent). Ratings of 4 or below are considered poor. The overall condition category is determined by the lowest individual component rating.
The fair condition rating of 5 indicates some deterioration that warrants monitoring but doesn't affect structural integrity.
For a structure built in 2016, this condition level is expected given the bridge's age and usage patterns. High traffic volumes on a bridge in fair or poor condition typically elevate its priority for rehabilitation or replacement in state transportation planning. If this bridge were closed, traffic would face a detour of approximately 18 miles, underscoring the importance of maintaining this crossing.
Bridge Details
Concrete is the primary structural material, which influences maintenance requirements and expected lifespan. The other design was selected based on span requirements, load capacity needs, and site conditions at the time of construction. Maintenance responsibility falls to State Highway Agency.
Construction
Dimensions
The maximum span length indicates this is a major crossing requiring specialized engineering. The deck area of 80,750 sq ft determines surface maintenance scope.
Classification
Status
Traffic Data
Traffic volume data helps engineers assess bridge wear patterns and plan maintenance schedules. Average Daily Traffic (ADT) counts are updated periodically and represent typical weekday usage.
56,378
Avg Daily Traffic (2022)
Vehicles per day crossing this bridge
3%
Truck Traffic
Commercial vehicle percentage
104,664
Projected Future ADT
Estimated future demand
This bridge carries approximately 56,378 vehicles per day, translating to roughly 20,577,970 crossings annually. This high volume places significant demands on the structure and necessitates frequent inspections.
Commercial trucks comprise 3% of traffic. Heavy vehicles cause disproportionate wear—a single fully loaded truck can have the impact of thousands of passenger cars on bridge deck surfaces.
Traffic projections estimate future volumes of 104,664 vehicles daily, a 86% increase from current levels. These projections inform capacity planning and potential upgrade requirements.
Load Ratings
Load ratings determine what weight this bridge can safely support. These values are critical for routing heavy vehicles and issuing overweight permits.
Operating Rating
5.0 tons
Maximum allowable load for special permits
Inventory Rating
3.9 tons
Load level for normal traffic
The operating rating of 5.0 tons represents the absolute maximum load this bridge can carry under controlled conditions with special permits. The inventory rating of 3.9 tons is the safe load limit for everyday traffic without restrictions. These relatively low ratings may result in posted weight limits or route restrictions for heavy vehicles.
5-Year Condition Trend
→StableCondition has remained relatively stable since 2020
Data: 2020-2024 FHWA National Bridge Inventory
Location
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48.611667, -122.997778
Identification
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Data Source: Federal Highway Administration (FHWA) National Bridge Inventory 2024
Bridge inspection data is typically updated every 24 months. Conditions may have changed since the last inspection.
“Structurally deficient” does not mean a bridge is unsafe or likely to collapse. It indicates that one or more key structural elements are in poor or worse condition. Bridges are inspected regularly and may have load restrictions in place.
This data is for informational purposes only and should not be used for route clearance or vehicle weight decisions.