US HIGHWAY 101 NB
over CALTRAIN UP RR GRAND ONR
04-SM-101-21.92-SSF, San Mateo County, California
Condition
PoorYear Built
1948
Daily Traffic
98,000
Length
73 ft
About This Bridge
US HIGHWAY 101 NB carries traffic over CALTRAIN UP RR GRAND ONR in San Mateo County, California. Built in 1948, this structure is 78 years old, making it a historic structure that has served the community for generations. 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 98,000 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 4% 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 poor condition based on federal inspection criteria established by the Federal Highway Administration. It is classified as structurally deficient, meaning one or more components have received a rating of 4 or below on the 0-9 scale. This designation indicates significant deterioration that warrants attention, though the bridge remains safe for travel within its posted limits. Structurally deficient does not mean unsafe—rather, it signals that repairs or replacement should be prioritized in transportation planning. With a total length of 73 feet, this is a shorter span typical of local road crossings, often carrying traffic over small streams, drainage channels, or other roadways.
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
Structurally Deficient
This bridge has one or more component ratings of 4 or below, indicating significant deterioration that requires attention. The bridge remains safe for travel but may have load restrictions.
Deck Condition
Poor
Superstructure
Good
Substructure
Good
Channel & Protection
N/A
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 deck rating of 4 indicates advanced deterioration affecting the driving surface.
For a structure built in 1948, the current condition reflects the cumulative effects of age, traffic, and environmental exposure. 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 3,863 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.
98,000
Avg Daily Traffic (2009)
Vehicles per day crossing this bridge
4%
Truck Traffic
Commercial vehicle percentage
121,559
Projected Future ADT
Estimated future demand
This bridge carries approximately 98,000 vehicles per day, translating to roughly 35,770,000 crossings annually. This high volume places significant demands on the structure and necessitates frequent inspections.
Commercial trucks comprise 4% 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 121,559 vehicles daily, a 24% 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
5.1 tons
Maximum allowable load for special permits
Inventory Rating
3.1 tons
Load level for normal traffic
The operating rating of 5.1 tons represents the absolute maximum load this bridge can carry under controlled conditions with special permits. The inventory rating of 3.1 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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37.968333, -123.085000
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.