320TH ST
Carrying 320TH ST over MUD CREEK
090443001, Plymouth, Iowa
Inventory: FHWA NBI 2024 · last ETL August 2026
FHWA NBI record, refreshed with each annual release.
320TH ST in Plymouth, Iowa sits above 23% of rated Iowa bridges on inventory load rating (21 t), while its 1900 build year is earlier than 91% of Plymouth's recorded-year cohort (432 bridges).
320TH ST in Plymouth, Iowa is rated Poor in the FHWA's 2024 National Bridge Inventory. Built in 1900, it carries 3 rated components on the inspecting agency's 0-9 scale, and its weakest reported component scores 3. 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 IA:000000000271170
PRE-1950 · STEEL · SINGLE-SPAN · SUB-LED · TRACE-ADT · STANDARD-LOAD · CAT-POOR
- PRE-1950 Pre-1950
- STEEL Steel
- SINGLE-SPAN Single span
- SUB-LED Substructure-led
- TRACE-ADT Trace 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: 320TH ST
The 320TH ST bridge in Plymouth, Iowa carries 320TH ST over MUD CREEK. It was built in 1900, making it 126 years old today. It was last reconstructed in 1973, extending its service life. The structure is built primarily of steel and spans 1 section, stretching 13.7 meters (45 feet) end to end. Daily traffic averages 11 vehicles, placing it in the lower-traffic tier of Iowa bridges. It is owned and maintained by County Highway Agency.
The latest FHWA inspection records show a deck rating of 7/9, superstructure at 6/9, substructure at 3/9. 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 320TH ST compares
Age against the county: built in 1900, earlier than 391 of Plymouth's 432 bridges with a recorded construction year (91%), against a county median build year of 1977. Age is not a defect on its own, but it is the population from which future Poor ratings are drawn.
Live comparison across Iowa bridges with a recorded inventory load rating (23,718 of 23,719 rated).
320TH ST vs every rated Iowa bridge
Inventory load rating (metric tons), FHWA NBI, this state
21 Top 77% higher than 23% of 23,718 bridges
rated Iowa 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.
Plymouth inventory by recorded NBI category
Exclusive Good/Fair/Poor bands across all 432 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
- 1900
- Last Reconstructed
- 1973
- Material
- Steel
- Number of Spans
- 1
- Structure Length
- 13.7 m (45 ft)
- Deck Width
- 5.6 m (18 ft)
- Owner
- County Highway Agency
- Avg Daily Traffic
- 11 vehicles/day
- Structure Number
- 000000000271170
Condition Analysis
- • At 7/9, the deck (driving surface) is in good shape and shows no significant wear.
- • The superstructure (beams and supports above the deck) is in fair condition (6/9), with minor deterioration that may require routine maintenance.
- • At 3/9, 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
320TH ST 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 320TH ST against other structures in Plymouth and across Iowa. Iowa 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 320TH ST?
320TH ST in Plymouth, Iowa has a deck rating of 7/9, superstructure rating of 6/9, and substructure rating of 3/9 on the FHWA's 0–9 scale.
How often is 320TH ST inspected?
320TH ST'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 11 vehicles per day.
What does “structurally deficient” mean in older bridge reports?
FHWA retired that reported status beginning with the 2018 archive. 320TH ST 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 320TH ST?
320TH ST has an NBI inventory load rating of 21.2 metric tons.
Who is responsible for maintaining 320TH ST?
320TH ST is owned and maintained by County Highway Agency.
How old is 320TH ST and does age affect safety?
320TH ST was built in 1900, making it 126 years old and last reconstructed in 1973.
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.
Share this inspection record
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.