US Bridges

21st St. over Butte Arm Canal

Fair

Bonneville County, Idaho · In Idaho FALLS;21st St. · Structure no. 000000000031320

Built
1955
70 years old
Condition
Fair
inspected March 2023
Type
Stringer/Multi-beam or Girder
Concrete
Length
35 ft
1 main span
Daily traffic
2,025
2023 count
Owner
City
City or Municipal Highway Agency

About this bridge

21st St. over Butte Arm Canal is a concrete stringer/multi-beam or girder carrying 21st St. over Butte Arm Canal in Bonneville County, Idaho. It was built in 1955, so it is 70 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.

It carries about 2,025 vehicles a day, roughly 10% of them trucks, projected to reach 3,038 by 2039. The structure is 35 ft (10.7 m) long and 70 ft wide. If it were closed, the detour would be 1.2 mi (2 km).

Location

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Carries21st St.
CrossesButte Arm Canal
LocationIn Idaho FALLS;21st St.
RouteCity Street 0
CountyBonneville County
StateIdaho
Coordinates43.47906, -112.03706
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.
Superstructure7 GoodSome minor problems.
Substructure7 GoodSome minor problems.
Channel and channel protection7 GoodSome minor problems.
Last inspectionMarch 2023
Inspection intervalevery 24 months
Operating statusOpen, no restriction
ScourFoundations stable; scour above top of footing
Structural evaluation5: Somewhat better than minimum adequacy to tolerate being left in place as is
Deck geometry5: Somewhat better than minimum adequacy to tolerate being left in place as is
Waterway adequacy8: Equal to present desirable criteria
Approach roadway alignment7: Better than present minimum criteria
Operating rating38 US tons
Inventory rating23 US tons

Structure

Structure typeStringer/Multi-beam or Girder
MaterialConcrete
DeckConcrete, cast-in-place
Main spans1
Design loadHS 20
Structure length35 ft (10.7 m)
Longest span34 ft (10.4 m)
Deck width70 ft (21.4 m)
Roadway width36 ft (11 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic2,025 (2023)
Projected traffic3,038 by 2039
Trucks10%
Lanes on structure2
Traffic directionTwo-way traffic
CarriesHighway and pedestrian
CrossesWaterway
Detour if closed1.2 mi (2 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 proposedNone recorded
Estimated improvement cost—
NavigationNo navigation control on waterway

Frequently asked questions

When was 21st St. over Butte Arm Canal built?

It was built in 1955, making it 70 years old in 2025.

What condition is 21st St. over Butte Arm Canal 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 21st St. over Butte Arm Canal carry?

About 2,025 vehicles per day (2023 count), of which roughly 10% are trucks.

How long is 21st St. over Butte Arm Canal?

The structure is 35 ft (10.7 m) long with a longest span of 34 ft (10.4 m) and a deck 70 ft wide.

Who owns 21st St. over Butte Arm Canal?

It is owned by the City or Municipal Highway Agency.