US Bridges

NB Ia 12 over US 20 & US 75

Fair

Woodbury County, Iowa · At Jct. US 20/US 75 · Structure no. 000000000603830

Built
1978
47 years old
Condition
Fair
inspected September 2024
Type
Stringer/Multi-beam or Girder
Prestressed Concrete
Length
289 ft
4 main spans
Daily traffic
6,100
2022 count
Owner
State
State Highway Agency

About this bridge

NB Ia 12 over US 20 & US 75 is a prestressed concrete stringer/multi-beam or girder carrying NB Ia 12 over US 20 & US 75 in Woodbury County, Iowa. It was built in 1978, so it is 47 years old, older than the Iowa average of 45.5 years.

The most recent inspection reported to the Federal Highway Administration rates it in fair condition with a lowest component rating of 5 out of 9. The lowest-rated primary component is rated 5 or 6. Minor deterioration is present but the structure is sound.

It carries about 6,100 vehicles a day, roughly 9% of them trucks, projected to reach 6,100 by 2044. The structure is 289 ft (88.1 m) long and 57 ft wide. If it were closed, the detour would be 1.2 mi (2 km).

Location

Open in Google Maps
CarriesNB Ia 12
CrossesUS 20 & US 75
LocationAt Jct. US 20/US 75
RouteState Highway 12
CountyWoodbury County
StateIowa
Coordinates42.47549, -96.32322
Functional classUrban Other Principal Arterial

Condition and inspection

Fair

The lowest-rated primary component is rated 5 or 6. Minor deterioration is present but the structure is sound.

ComponentRatingMeaning
Deck6 SatisfactoryStructural elements show some minor deterioration.
Superstructure5 FairAll primary structural elements are sound but may have minor section loss, cracking, spalling or scour.
Substructure5 FairAll primary structural elements are sound but may have minor section loss, cracking, spalling or scour.
Last inspectionSeptember 2024
Inspection intervalevery 24 months
Operating statusOpen, no restriction
ScourBridge not over waterway
Structural evaluation5: Somewhat better than minimum adequacy to tolerate being left in place as is
Deck geometry7: Better than present minimum criteria
Approach roadway alignment6: Equal to present minimum criteria
Operating rating79.6 US tons
Inventory rating29.1 US tons

Structure

Structure typeStringer/Multi-beam or Girder
MaterialPrestressed Concrete
DeckConcrete, cast-in-place
Main spans4
Design loadHS 20
Structure length289 ft (88.1 m)
Longest span92 ft (28 m)
Deck width57 ft (17.5 m)
Roadway width54 ft (16.5 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic6,100 (2022)
Projected traffic6,100 by 2044
Trucks9%
Lanes on structure3
Traffic directionOne-way traffic
CarriesOverpass structure at an interchange
CrossesHighway
Detour if closed1.2 mi (2 km)
TollOn a free road
National Highway SystemYes

Ownership and planned work

OwnerState Highway Agency
Maintained byState Highway Agency
Historic statusNot eligible for the National Register of Historic Places
Work proposedNone recorded
Estimated improvement cost—
NavigationNot applicable (no waterway)

Frequently asked questions

When was NB Ia 12 over US 20 & US 75 built?

It was built in 1978, making it 47 years old in 2025.

What condition is NB Ia 12 over US 20 & US 75 in?

The National Bridge Inventory rates it in fair condition. The lowest-rated primary component is rated 5 or 6. Minor deterioration is present but the structure is sound. The last reported inspection was in September 2024.

How much traffic does NB Ia 12 over US 20 & US 75 carry?

About 6,100 vehicles per day (2022 count), of which roughly 9% are trucks.

How long is NB Ia 12 over US 20 & US 75?

The structure is 289 ft (88.1 m) long with a longest span of 92 ft (28 m) and a deck 57 ft wide.

Who owns NB Ia 12 over US 20 & US 75?

It is owned by the State Highway Agency.