IS 55 S
over MERAMEC RVR
S 403 T 43 N R 6 E, St. Louis County, Missouri
Condition
FairYear Built
1964
Daily Traffic
61,319
Length
143 ft
About This Bridge
IS 55 S carries traffic over MERAMEC RVR in St. Louis County, Missouri. Built in 1964, this structure is 62 years old, placing it among the older bridges still in active service. The bridge features steel continuous construction with a stringer/multi-beam or girder design, a combination chosen by engineers to meet the specific requirements of this crossing.
Approximately 61,319 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 18% of all crossings. This heavy commercial usage significantly impacts structural wear, as a single fully-loaded truck can cause as much deck wear as thousands of passenger vehicles. Transportation planners factor this into maintenance scheduling and budget allocation.
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 143 feet, this structure falls within the typical range requiring standard inspection procedures conducted by certified bridge inspectors.
The construction materials used in this bridge were selected based on engineering requirements, cost considerations, and local conditions at the time of construction.
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
Fair
Substructure
Good
Channel & Protection
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 1964, 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.
Bridge Details
Steel Continuous is the primary structural material, which influences maintenance requirements and expected lifespan. The stringer/multi-beam or girder 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
Span dimensions affect structural design choices and load distribution. The deck area of 10,119 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.
61,319
Avg Daily Traffic (2023)
Vehicles per day crossing this bridge
18%
Truck Traffic
Commercial vehicle percentage
76,649
Projected Future ADT
Estimated future demand
This bridge carries approximately 61,319 vehicles per day, translating to roughly 22,381,435 crossings annually. This high volume places significant demands on the structure and necessitates frequent inspections.
Commercial trucks comprise 18% 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. This high percentage of truck traffic may accelerate deterioration of deck surfaces and structural components.
Traffic projections estimate future volumes of 76,649 vehicles daily, a 25% 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
4.7 tons
Maximum allowable load for special permits
Inventory Rating
2.8 tons
Load level for normal traffic
The operating rating of 4.7 tons represents the absolute maximum load this bridge can carry under controlled conditions with special permits. The inventory rating of 2.8 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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38.739444, -91.375278
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.