US Bridges

R38/500th Ave over Onion Creek

Fair

Story County, Iowa · 084243002 · Structure no. 000000000315640

Built
1970
55 years old
Condition
Fair
inspected December 2022
Type
Slab
Concrete Continuous
Length
100 ft
3 main spans
Daily traffic
2,404
2022 count
Owner
County
County Highway Agency

About this bridge

R38/500th Ave over Onion Creek is a concrete continuous slab carrying R38/500th Ave over Onion Creek in Story County, Iowa. It was built in 1970, so it is 55 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 2,404 vehicles a day, roughly 9% of them trucks, projected to reach 2,404 by 2043. The structure is 100 ft (30.5 m) long and 36 ft wide. If it were closed, the detour would be 3.7 mi (6 km).

Location

Open in Google Maps
CarriesR38/500th Ave
CrossesOnion Creek
Location084243002
RouteCounty Highway 0
CountyStory County
StateIowa
Coordinates42.05338, -93.6987
Functional classRural Major Collector

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.
Substructure6 SatisfactoryStructural elements show some minor deterioration.
Channel and channel protection7 GoodSome minor problems.
Last inspectionDecember 2022
Inspection intervalevery 24 months
Operating statusOpen, no restriction
ScourFoundations stable; scour above top of footing
Structural evaluation6: Equal to present minimum criteria
Deck geometry5: Somewhat better than minimum adequacy to tolerate being left in place as is
Waterway adequacy8: Equal to present desirable criteria
Approach roadway alignment8: Equal to present desirable criteria
Operating rating51.7 US tons
Inventory rating31 US tons

Structure

Structure typeSlab
MaterialConcrete Continuous
DeckConcrete, cast-in-place
Main spans3
Design loadH 20
Structure length100 ft (30.5 m)
Longest span39 ft (11.9 m)
Deck width36 ft (11 m)
Roadway width34 ft (10.4 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic2,404 (2022)
Projected traffic2,404 by 2043
Trucks9%
Lanes on structure2
Traffic directionTwo-way traffic
CarriesHighway
CrossesWaterway
Detour if closed3.7 mi (6 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 proposedReplacement because of substandard load-carrying capacity or roadway geometry
Estimated improvement cost—
NavigationNo navigation control on waterway

Frequently asked questions

When was R38/500th Ave over Onion Creek built?

It was built in 1970, making it 55 years old in 2025.

What condition is R38/500th Ave over Onion 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 December 2022.

How much traffic does R38/500th Ave over Onion Creek carry?

About 2,404 vehicles per day (2022 count), of which roughly 9% are trucks.

How long is R38/500th Ave over Onion Creek?

The structure is 100 ft (30.5 m) long with a longest span of 39 ft (11.9 m) and a deck 36 ft wide.

Who owns R38/500th Ave over Onion Creek?

It is owned by the County Highway Agency.