US Bridges

NB I-29 over Big Sioux River

Fair

Woodbury County, Iowa · South Dakota State Line · Structure no. 000000000053930

Built
1963
62 years old
Condition
Fair
inspected April 2023
Type
Stringer/Multi-beam or Girder
Steel Continuous
Length
560 ft
3 main spans
Daily traffic
17,650
2022 count
Owner
State
State Highway Agency

About this bridge

NB I-29 over Big Sioux River is a steel continuous stringer/multi-beam or girder carrying NB I-29 over Big Sioux River in Woodbury County, Iowa. It was built in 1963, so it is 62 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 6 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 17,650 vehicles a day, roughly 17% of them trucks, projected to reach 17,650 by 2043. The structure is 560 ft (170.7 m) long and 36 ft wide. If it were closed, the detour would be 1.2 mi (2 km).

Location

Open in Google Maps
CarriesNB I-29
CrossesBig Sioux River
LocationSouth Dakota State Line
RouteInterstate 29
CountyWoodbury County
StateIowa
Coordinates42.49507, -96.47609
Functional classUrban 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
Deck6 SatisfactoryStructural elements show some minor deterioration.
Superstructure7 GoodSome minor problems.
Substructure6 SatisfactoryStructural elements show some minor deterioration.
Channel and channel protection8 Very GoodNo problems noted.
Last inspectionApril 2023
Inspection intervalevery 24 months
Operating statusOpen, no restriction
ScourFoundations stable; scour within limits of footing or piles
Structural evaluation6: Equal to present minimum criteria
Deck geometry4: Meets minimum tolerable limits to be left in place as is
Waterway adequacy8: Equal to present desirable criteria
Approach roadway alignment8: Equal to present desirable criteria
Operating rating61 US tons
Inventory rating36 US tons

Structure

Structure typeStringer/Multi-beam or Girder
MaterialSteel Continuous
DeckConcrete, cast-in-place
Main spans3
Design loadHS 20 + Mod
Structure length560 ft (170.7 m)
Longest span225 ft (68.6 m)
Deck width36 ft (11 m)
Roadway width30 ft (9.1 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic17,650 (2022)
Projected traffic17,650 by 2043
Trucks17%
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 Big Sioux River built?

It was built in 1963, making it 62 years old in 2025.

What condition is NB I-29 over Big Sioux River 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 2023.

How much traffic does NB I-29 over Big Sioux River carry?

About 17,650 vehicles per day (2022 count), of which roughly 17% are trucks.

How long is NB I-29 over Big Sioux River?

The structure is 560 ft (170.7 m) long with a longest span of 225 ft (68.6 m) and a deck 36 ft wide.

Who owns NB I-29 over Big Sioux River?

It is owned by the State Highway Agency.