MILL STATION RD
Carrying MILL STATION RD over ATASCADERO CR OVERFLOW
0.2 MI E FERGUSON RD, Sonoma, California
Inventory: FHWA NBI 2024 · last ETL August 2026
FHWA NBI record, refreshed with each annual release.
MILL STATION RD in Sonoma, California sits above 74% of rated California bridges on inventory load rating (33 t), while its 1964 build year is earlier than 52% of Sonoma's recorded-year cohort (609 bridges).
MILL STATION RD in Sonoma, California is rated Poor in the FHWA's 2024 National Bridge Inventory. Built in 1964, it carries 3 rated components on the inspecting agency's 0-9 scale, and its weakest reported component scores 4. The lowest applicable rating sets the federal condition category, so this Poor result describes the weakest reported component rather than the structure as a whole. No NBI category is a closure decision or a live crossing-safety verdict.
NBI record plate
Structure CA:20C0315
INTERSTATE-ERA · CONCRETE · LONG-SPAN-RUN · SUB-LED · ARTERIAL-ADT · STANDARD-LOAD · CAT-POOR
- INTERSTATE-ERA 1950–1979
- CONCRETE Concrete
- LONG-SPAN-RUN 4 spans
- SUB-LED Substructure-led
- ARTERIAL-ADT Arterial ADT
- STANDARD-LOAD Standard load
- CAT-POOR Poor
Inspection-sheet codes from this record’s year, material family, spans, controlling component, ADT, inventory load, and NBI category, not a live closure verdict.
Bridge Snapshot: MILL STATION RD
The MILL STATION RD bridge in Sonoma, California carries MILL STATION RD over ATASCADERO CR OVERFLOW. It was built in 1964, making it 62 years old today. The structure is built primarily of concrete continuous and spans 4 sections, stretching 29.0 meters (95 feet) end to end. Daily traffic averages 1,450 vehicles, placing it in the moderately-trafficked tier of California bridges. It is owned and maintained by County Highway Agency.
The latest FHWA inspection records show a deck rating of 5/9, superstructure at 5/9, substructure at 4/9. The weakest component sits in poor condition. A component scored 4 or below, placing this bridge in the federal Poor condition category rather than declaring it unsafe or closed.
How MILL STATION RD compares
Age against the county: built in 1964, earlier than 315 of Sonoma's 609 bridges with a recorded construction year (52%), against a county median build year of 1966. Age is not a defect on its own, but it is the population from which future Poor ratings are drawn.
Live comparison across California bridges with a recorded inventory load rating (25,538 of 25,848 rated).
MILL STATION RD vs every rated California bridge
Inventory load rating (metric tons), FHWA NBI, this state
33 Top 26% higher than 74% of 25,538 bridges
rated California bridges, bucketed by value
Each bar is a band; taller bars hold more bridges. The dashed line + filled bar mark this entry. Hover or tap any bar for its full count and share, and where it sits relative to this entry.
Source FHWA National Bridge Inventory · August 2026
Condition Ratings
Full 0–9 scale + sufficiency-rating breakdown: how condition ratings work.
Reported 0–9 component ratings from the FHWA NBI. The highlighted component is the lowest reported input to this record’s current condition category; it is not a closure or live crossing-safety decision.
Sonoma inventory by recorded NBI category
Exclusive Good/Fair/Poor bands across all 609 bridges in this county. Orthogonal to this structure's component profile above: a county catalog share, not a live crossing-safety verdict.
Structural Details
- Year Built
- 1964
- Material
- Concrete Continuous
- Number of Spans
- 4
- Structure Length
- 29.0 m (95 ft)
- Deck Width
- 9.9 m (32 ft)
- Owner
- County Highway Agency
- Avg Daily Traffic
- 1,450 vehicles/day
- Structure Number
- 20C0315
Condition Analysis
- • The deck (driving surface) is in fair condition (5/9), with minor deterioration that may require routine maintenance.
- • The superstructure (beams and supports above the deck) rates fair at 5/9, minor deterioration that routine maintenance should address.
- • At 4/9, the substructure (piers and abutments) is in poor shape, with advanced wear on file for this vintage.
Location
Data Source
FHWA National Bridge Inventory (NBI).
FHWA NBI Program ↗How to read this record
MILL STATION RD is in the federal Poor condition category. That is a component-based result, not a closure order.
- NBI condition ratings reflect the latest record in this annual dataset, not a live status. Current routine inspection intervals are risk-based.
- Understand what Poor condition does and does not mean before drawing conclusions. Poor condition explained
- Compare MILL STATION RD against other structures in Sonoma and across California. California bridges
- Noticed visible damage or a safety concern? Report it to the agency that owns the bridge, or call 911 in an emergency. How to report a bridge
Condition codes come straight from the FHWA National Bridge Inventory and are not a real-time safety judgment. Only the owning agency, a state DOT, county, or other owner, can post, restrict, or close a bridge.
Frequently Asked Questions
What do the condition ratings mean for MILL STATION RD?
MILL STATION RD in Sonoma, California has a deck rating of 5/9, superstructure rating of 5/9, and substructure rating of 4/9 on the FHWA's 0–9 scale.
How often is MILL STATION RD inspected?
MILL STATION RD's responsible agency sets its routine interval under FHWA's risk-based inspection rules; this page does not expose the scheduled interval. It carries about 1,450 vehicles per day.
What does “structurally deficient” mean in older bridge reports?
FHWA retired that reported status beginning with the 2018 archive. MILL STATION RD is currently shown as Poor condition from its component ratings; that category is not a live closure or safety decision.
What is the inventory load rating for MILL STATION RD?
MILL STATION RD has an NBI inventory load rating of 33.0 metric tons.
Who is responsible for maintaining MILL STATION RD?
MILL STATION RD is owned and maintained by County Highway Agency.
How old is MILL STATION RD and does age affect safety?
MILL STATION RD was built in 1964, making it 62 years old.
Disclaimer: Bridge condition data is from the FHWA NBI and reflects the last reported inspection. A Poor condition rating is not a live declaration that a bridge is closed or unsafe for travel. For current closure, posting, or safety information, contact the responsible transportation agency.
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Send this source-bounded record or download its data card. An NBI condition category is not a closure or live crossing-safety verdict.
Every figure on PlainBridges is rendered directly from federal source data, no number is typed in by an editor. Component ratings, ADT, and condition category on this page are copied from the NBI record for this structure; no figure is typed in by an editor. See our editorial standards & corrections policy, the methodology behind these numbers, or report a data error. Data current as of 2024 NBI release. NBI condition categories reflect the latest reported inventory record, not a live safety, closure, or travel decision.