US Bridges

170th ST over Skunk River

FairPosted for load

Story County, Iowa · 084230703 · Structure no. 000000000315280

Built
1939
86 years old
Condition
Fair
inspected December 2022
Type
Truss - Thru
Steel
Length
152 ft
1 main span
Daily traffic
139
2022 count
Owner
County
County Highway Agency

About this bridge

170th ST over Skunk River is a steel truss - thru carrying 170th ST over Skunk River in Story County, Iowa. It was built in 1939, so it is 86 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. Its operating status is: posted for other load-capacity restriction.

It carries about 139 vehicles a day, projected to reach 139 by 2043. The structure is 152 ft (46.3 m) long and 21 ft wide. If it were closed, the detour would be 6.2 mi (10 km).

Location

Open in Google Maps
Carries170th ST
CrossesSkunk River
Location084230703
RouteCounty Highway 0
CountyStory County
StateIowa
Coordinates42.10619, -93.57086
Functional classRural 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
Deck5 FairAll primary structural elements are sound but may have minor section loss, cracking, spalling or scour.
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 inspectionDecember 2022
Inspection intervalevery 24 months
Operating statusPosted for other load-capacity restriction
ScourFoundations stable; scour above top of footing
Structural evaluation5: Somewhat better than minimum adequacy to tolerate being left in place as is
Deck geometry2: Basically intolerable, requiring high priority of replacement
Waterway adequacy7: Better than present minimum criteria
Approach roadway alignment2: Basically intolerable, requiring high priority of replacement
Operating rating46 US tons
Inventory rating31 US tons

Structure

Structure typeTruss - Thru
MaterialSteel
DeckConcrete, cast-in-place
Main spans1
Design loadUnknown
Structure length152 ft (46.3 m)
Longest span150 ft (45.7 m)
Deck width21 ft (6.5 m)
Roadway width20 ft (6.1 m)
Vertical clearance over deck12 ft (3.6 m)

Traffic and service

Average daily traffic139 (2022)
Projected traffic139 by 2043
Trucks0%
Lanes on structure2
Traffic directionTwo-way traffic
CarriesHighway
CrossesWaterway
Detour if closed6.2 mi (10 km)
TollOn a free road
National Highway SystemNo

Ownership and planned work

OwnerCounty Highway Agency
Maintained byCounty Highway Agency
Historic statusPossibly eligible for the National Register; requires further investigation
Work proposedReplacement because of substandard load-carrying capacity or roadway geometry
Estimated improvement cost—
NavigationNo navigation control on waterway

Frequently asked questions

When was 170th ST over Skunk River built?

It was built in 1939, making it 86 years old in 2025.

What condition is 170th ST over Skunk 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 December 2022.

How much traffic does 170th ST over Skunk River carry?

About 139 vehicles per day (2022 count).

How long is 170th ST over Skunk River?

The structure is 152 ft (46.3 m) long with a longest span of 150 ft (45.7 m) and a deck 21 ft wide.

Who owns 170th ST over Skunk River?

It is owned by the County Highway Agency.