US Bridges

NB I-29 over Drainage Ditch

Fair

Harrison County, Iowa · 1.6 Mi. N of Jct. SR F-20 · Structure no. 000000000028380

Built
1966
59 years old
Condition
Fair
inspected April 2022
Type
Girder and Floorbeam System
Steel Continuous
Length
316 ft
3 main spans
Daily traffic
7,250
2022 count
Owner
State
State Highway Agency

About this bridge

NB I-29 over Drainage Ditch is a steel continuous girder and floorbeam system carrying NB I-29 over Drainage Ditch in Harrison County, Iowa. It was built in 1966, so it is 59 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 7,250 vehicles a day, roughly 32% of them trucks, projected to reach 7,250 by 2042. The structure is 316 ft (96.3 m) long and 33 ft wide. If it were closed, the detour would be 1.2 mi (2 km).

Location

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CarriesNB I-29
CrossesDrainage Ditch
Location1.6 Mi. N of Jct. SR F-20
RouteInterstate 29
CountyHarrison County
StateIowa
Coordinates41.82058, -96.07219
Functional classRural Principal Arterial - Interstate

Condition and inspection

Fair

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

ComponentRatingMeaning
Deck7 GoodSome minor problems.
Superstructure5 FairAll primary structural elements are sound but may have minor section loss, cracking, spalling or scour.
Substructure6 SatisfactoryStructural elements show some minor deterioration.
Channel and channel protection7 GoodSome minor problems.
Last inspectionApril 2022
Inspection intervalevery 24 months
Operating statusOpen, no restriction
ScourFoundations stable; scour above top of footing
Structural evaluation5: Somewhat better than minimum adequacy to tolerate being left in place as is
Deck geometry4: Meets minimum tolerable limits to be left in place as is
Waterway adequacy6: Equal to present minimum criteria
Approach roadway alignment8: Equal to present desirable criteria
Operating rating48.1 US tons
Inventory rating28.9 US tons

Structure

Structure typeGirder and Floorbeam System
MaterialSteel Continuous
DeckConcrete, cast-in-place
Main spans3
Design loadHS 20
Structure length316 ft (96.3 m)
Longest span121 ft (36.9 m)
Deck width33 ft (10.2 m)
Roadway width30 ft (9.1 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic7,250 (2022)
Projected traffic7,250 by 2042
Trucks32%
Lanes on structure2
Traffic directionOne-way traffic
CarriesHighway
CrossesWaterway
Detour if closed1.2 mi (2 km)
TollOn a free road
National Highway SystemYes
Strategic Highway NetworkInterstate STRAHNET route

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—
NavigationNo navigation control on waterway

Frequently asked questions

When was NB I-29 over Drainage Ditch built?

It was built in 1966, making it 59 years old in 2025.

What condition is NB I-29 over Drainage Ditch 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 April 2022.

How much traffic does NB I-29 over Drainage Ditch carry?

About 7,250 vehicles per day (2022 count), of which roughly 32% are trucks.

How long is NB I-29 over Drainage Ditch?

The structure is 316 ft (96.3 m) long with a longest span of 121 ft (36.9 m) and a deck 33 ft wide.

Who owns NB I-29 over Drainage Ditch?

It is owned by the State Highway Agency.