US Bridges

Capitol Avenue over Swauger Slough

FairPosted for load

Custer County, Idaho · In Mackay · Structure no. 000000000031815

Built
1940
85 years old, rebuilt 1999
Condition
Fair
inspected July 2023
Type
Stringer/Multi-beam or Girder
Steel
Length
23 ft
1 main span
Daily traffic
1,220
2023 count
Owner
City
City or Municipal Highway Agency

About this bridge

Capitol Avenue over Swauger Slough is a steel stringer/multi-beam or girder carrying Capitol Avenue over Swauger Slough in Custer County, Idaho. It was built in 1940 and reconstructed in 1999, so it is 85 years old, older than the Idaho average of 45.3 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. Its operating status is: posted for load restriction.

It carries about 1,220 vehicles a day, roughly 5% of them trucks, projected to reach 1,830 by 2039. The structure is 23 ft (7 m) long and 20 ft wide. If it were closed, the detour would be 98.8 mi (159 km).

Location

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CarriesCapitol Avenue
CrossesSwauger Slough
LocationIn Mackay
RouteCity Street 0
CountyCuster County
StateIdaho
Coordinates43.91136, -113.61878
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
Deck7 GoodSome minor problems.
Superstructure7 GoodSome minor problems.
Substructure6 SatisfactoryStructural elements show some minor deterioration.
Channel and channel protection6 SatisfactoryStructural elements show some minor deterioration.
Last inspectionJuly 2023
Inspection intervalevery 24 months
Operating statusPosted for load restriction
ScourUnknown foundation; not evaluated for scour
Structural evaluation2: Basically intolerable, requiring high priority of replacement
Deck geometry2: Basically intolerable, requiring high priority of replacement
Waterway adequacy7: Better than present minimum criteria
Approach roadway alignment8: Equal to present desirable criteria
Operating rating18 US tons
Inventory rating11 US tons

Structure

Structure typeStringer/Multi-beam or Girder
MaterialSteel
DeckCorrugated steel
Main spans1
Design loadH 10
Structure length23 ft (7 m)
Longest span22 ft (6.7 m)
Deck width20 ft (6.2 m)
Roadway width20 ft (6.2 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic1,220 (2023)
Projected traffic1,830 by 2039
Trucks5%
Lanes on structure1
Traffic directionOne-lane bridge for two-way traffic
CarriesHighway
CrossesWaterway
Detour if closed98.8 mi (159 km)
TollOn a free road
National Highway SystemNo

Ownership and planned work

OwnerCity or Municipal Highway Agency
Maintained byCity or Municipal Highway Agency
Historic statusHistorical significance not determinable at this time
Work proposedReplacement because of substandard load-carrying capacity or roadway geometry
Estimated improvement cost$451,000 (2019 estimate)
NavigationNo navigation control on waterway

Frequently asked questions

When was Capitol Avenue over Swauger Slough built?

It was built in 1940, making it 85 years old in 2025. It was reconstructed in 1999.

What condition is Capitol Avenue over Swauger Slough 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 July 2023.

How much traffic does Capitol Avenue over Swauger Slough carry?

About 1,220 vehicles per day (2023 count), of which roughly 5% are trucks.

How long is Capitol Avenue over Swauger Slough?

The structure is 23 ft (7 m) long with a longest span of 22 ft (6.7 m) and a deck 20 ft wide.

Who owns Capitol Avenue over Swauger Slough?

It is owned by the City or Municipal Highway Agency.