US Bridges

NB I-29 over Robinson Ditch

Good

Monona County, Iowa · 4.1 Mi. S of Jct. Ia 141 · Structure no. 000000000037351

Built
2011
14 years old
Condition
Good
inspected April 2024
Type
Slab
Concrete Continuous
Length
103 ft
3 main spans
Daily traffic
7,800
2022 count
Owner
State
State Highway Agency

About this bridge

NB I-29 over Robinson Ditch is a concrete continuous slab carrying NB I-29 over Robinson Ditch in Monona County, Iowa. It was built in 2011, so it is 14 years old, younger than the Iowa average of 45.5 years.

The most recent inspection reported to the Federal Highway Administration rates it in good condition with a lowest component rating of 8 out of 9. All primary components (deck, superstructure, substructure, or culvert) are rated 7 or higher. No significant problems were noted.

It carries about 7,800 vehicles a day, roughly 31% of them trucks, projected to reach 7,800 by 2044. The structure is 103 ft (31.4 m) long and 43 ft wide. If it were closed, the detour would be 1.2 mi (2 km).

Location

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CarriesNB I-29
CrossesRobinson Ditch
Location4.1 Mi. S of Jct. Ia 141
RouteInterstate 29
CountyMonona County
StateIowa
Coordinates42.17105, -96.22962
Functional classRural Principal Arterial - Interstate

Condition and inspection

Good

All primary components (deck, superstructure, substructure, or culvert) are rated 7 or higher. No significant problems were noted.

ComponentRatingMeaning
Deck8 Very GoodNo problems noted.
Superstructure8 Very GoodNo problems noted.
Substructure8 Very GoodNo problems noted.
Channel and channel protection8 Very GoodNo problems noted.
Last inspectionApril 2024
Inspection intervalevery 24 months
Operating statusOpen, no restriction
ScourFoundations stable; scour above top of footing
Structural evaluation8: Equal to present desirable criteria
Deck geometry7: Better than present minimum criteria
Waterway adequacy9: Superior to present desirable criteria
Approach roadway alignment8: Equal to present desirable criteria
Operating rating46.4 US tons
Inventory rating35.7 US tons

Structure

Structure typeSlab
MaterialConcrete Continuous
DeckConcrete, cast-in-place
Main spans3
Design loadHL 93
Structure length103 ft (31.4 m)
Longest span39 ft (11.9 m)
Deck width43 ft (13.2 m)
Roadway width40 ft (12.2 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic7,800 (2022)
Projected traffic7,800 by 2044
Trucks31%
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 Robinson Ditch built?

It was built in 2011, making it 14 years old in 2025.

What condition is NB I-29 over Robinson Ditch in?

The National Bridge Inventory rates it in good condition. All primary components (deck, superstructure, substructure, or culvert) are rated 7 or higher. No significant problems were noted. The last reported inspection was in April 2024.

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

About 7,800 vehicles per day (2022 count), of which roughly 31% are trucks.

How long is NB I-29 over Robinson Ditch?

The structure is 103 ft (31.4 m) long with a longest span of 39 ft (11.9 m) and a deck 43 ft wide.

Who owns NB I-29 over Robinson Ditch?

It is owned by the State Highway Agency.