US 18 over Big Sioux River
FairLyon County, Iowa · At S.Dakota Border · Structure no. 000000000034481
- Built
- 1978
- 47 years old
- Condition
- Fair
- inspected March 2024
- Type
- Stringer/Multi-beam or Girder
- Steel Continuous
- Length
- 580 ft
- 4 main spans
- Daily traffic
- 2,130
- 2022 count
- Owner
- State
- State Highway Agency
About this bridge
US 18 over Big Sioux River is a steel continuous stringer/multi-beam or girder carrying US 18 over Big Sioux River in Lyon County, Iowa. It was built in 1978, so it is 47 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.
It carries about 2,130 vehicles a day, roughly 20% of them trucks, projected to reach 2,130 by 2044. The structure is 580 ft (176.8 m) long and 47 ft wide. If it were closed, the detour would be 24.2 mi (39 km).
Location
Open in Google MapsCondition and inspection
The lowest-rated primary component is rated 5 or 6. Minor deterioration is present but the structure is sound.
| Component | Rating | Meaning |
|---|---|---|
| Deck | 5 Fair | All primary structural elements are sound but may have minor section loss, cracking, spalling or scour. |
| Superstructure | 6 Satisfactory | Structural elements show some minor deterioration. |
| Substructure | 7 Good | Some minor problems. |
| Channel and channel protection | 7 Good | Some minor problems. |
Structure
Traffic and service
Ownership and planned work
Frequently asked questions
When was US 18 over Big Sioux River built?
It was built in 1978, making it 47 years old in 2025.
What condition is US 18 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 March 2024.
How much traffic does US 18 over Big Sioux River carry?
About 2,130 vehicles per day (2022 count), of which roughly 20% are trucks.
How long is US 18 over Big Sioux River?
The structure is 580 ft (176.8 m) long with a longest span of 162 ft (49.4 m) and a deck 47 ft wide.
Who owns US 18 over Big Sioux River?
It is owned by the State Highway Agency.