US Bridges

Linn-Johnson RD over Knapp Creek

Fair

Johnson County, Iowa · 081080601 · Structure no. 000000000205741

Built
1984
41 years old
Condition
Fair
inspected March 2023
Type
Slab
Concrete Continuous
Length
127 ft
3 main spans
Daily traffic
46
2021 count
Owner
County
County Highway Agency

About this bridge

Linn-Johnson RD over Knapp Creek is a concrete continuous slab carrying Linn-Johnson RD over Knapp Creek in Johnson County, Iowa. It was built in 1984, so it is 41 years old, younger 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 46 vehicles a day, roughly 28% of them trucks, projected to reach 46 by 2043. The structure is 127 ft (38.7 m) long and 33 ft wide. If it were closed, the detour would be 3.1 mi (5 km).

Location

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CarriesLinn-Johnson RD
CrossesKnapp Creek
Location081080601
RouteCounty Highway 0
CountyJohnson County
StateIowa
Coordinates41.86185, -91.82729
Functional classUrban Local

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.
Superstructure6 SatisfactoryStructural elements show some minor deterioration.
Substructure7 GoodSome minor problems.
Channel and channel protection6 SatisfactoryStructural elements show some minor deterioration.
Last inspectionMarch 2023
Inspection intervalevery 24 months
Operating statusOpen, no restriction
ScourFoundations stable; scour above top of footing
Structural evaluation6: Equal to present minimum criteria
Deck geometry7: Better than present minimum criteria
Waterway adequacy8: Equal to present desirable criteria
Approach roadway alignment8: Equal to present desirable criteria
Operating rating59.5 US tons
Inventory rating35.6 US tons

Structure

Structure typeSlab
MaterialConcrete Continuous
DeckConcrete, cast-in-place
Main spans3
Design loadHS 20
Structure length127 ft (38.7 m)
Longest span46 ft (14 m)
Deck width33 ft (10.1 m)
Roadway width30 ft (9.1 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic46 (2021)
Projected traffic46 by 2043
Trucks28%
Lanes on structure2
Traffic directionTwo-way traffic
CarriesHighway
CrossesWaterway
Detour if closed3.1 mi (5 km)
TollOn a free road
National Highway SystemNo

Ownership and planned work

OwnerCounty Highway Agency
Maintained byCounty 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 Linn-Johnson RD over Knapp Creek built?

It was built in 1984, making it 41 years old in 2025.

What condition is Linn-Johnson RD over Knapp Creek 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 March 2023.

How much traffic does Linn-Johnson RD over Knapp Creek carry?

About 46 vehicles per day (2021 count), of which roughly 28% are trucks.

How long is Linn-Johnson RD over Knapp Creek?

The structure is 127 ft (38.7 m) long with a longest span of 46 ft (14 m) and a deck 33 ft wide.

Who owns Linn-Johnson RD over Knapp Creek?

It is owned by the County Highway Agency.