KOOCANUSA BRIDGE

over KOOCANUSA RESERVOIR

LAKE KOOCANUSA, Lincoln County, Montana

Condition

Fair

Year Built

1971

Daily Traffic

75

Length

244 ft

About This Bridge

KOOCANUSA BRIDGE carries traffic over KOOCANUSA RESERVOIR in Lincoln County, Montana. Built in 1971, this structure is 55 years old, placing it among the older bridges still in active service. The bridge features steel construction with a truss - deck design, a combination chosen by engineers to meet the specific requirements of this crossing.

Approximately 75 vehicles cross this bridge daily, indicating lower traffic volumes common for local roads and rural routes. While traffic is lighter, these bridges still serve essential community transportation needs.

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 244 feet, this structure falls within the typical range requiring standard inspection procedures conducted by certified bridge inspectors.

Steel bridges provide high strength-to-weight ratios, making them suitable for longer spans. However, they require ongoing protection against corrosion through painting or weathering steel designs. Inspectors pay close attention to connection points, fatigue cracking, and coating condition.

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

6

Deck Condition

Satisfactory

6

Superstructure

Satisfactory

6

Substructure

Satisfactory

7

Channel & Protection

Good

6

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 6 indicates satisfactory condition with minor section loss or deterioration.

For a structure built in 1971, this condition level is expected given the bridge's age and usage patterns. If this bridge were closed, traffic would face a detour of approximately 85 miles, underscoring the importance of maintaining this crossing.

Bridge Details

Steel is the primary structural material, which influences maintenance requirements and expected lifespan. The truss - deck design was selected based on span requirements, load capacity needs, and site conditions at the time of construction. Maintenance responsibility falls to U.S. Forest Service.

Construction

Year Built1971
Year Reconstructed1983
MaterialSteel
Design TypeTruss - Deck
OwnerU.S. Forest Service

Dimensions

Total Length244 ft (74.3 m)
Max Span238 ft (72.6 m)
Deck Width3 ft
Deck Area7,577 sq ft

The maximum span length indicates this is a major crossing requiring specialized engineering. The deck area of 7,577 sq ft determines surface maintenance scope.

Classification

Route TypeFederal Lands
Route Number92
Lanes On Bridge2
Lanes Under Bridge

Status

Toll BridgeNo
Historical SignificanceNot determined
Scour Critical8
Detour Length85 mi (136 km)

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.

75

Avg Daily Traffic (1990)

Vehicles per day crossing this bridge

Truck Traffic

Commercial vehicle percentage

112

Projected Future ADT

Estimated future demand

This bridge carries approximately 75 vehicles per day, translating to roughly 27,375 crossings annually. Lower traffic volumes generally result in less structural wear over time.

Traffic projections estimate future volumes of 112 vehicles daily, a 49% 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

Maximum allowable load for special permits

Inventory Rating

Load level for normal traffic

5-Year Condition Trend

Declining

Condition has declined by 1.0 rating points since 2020

Data: 2020-2024 FHWA National Bridge Inventory

Location

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49.943889, -115.690000

Identification

Structure Number011401000000046
NBI IDMT-011401000000046
State FIPS30
County FIPS053

Explore More

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.

KOOCANUSA BRIDGE over KOOCANUSA RESERVOIR, Montana — Bridge Condition | BridgeReport.org | BridgeReport.org