US Bridges

SH 75 over Salmon River

Fair

Custer County, Idaho · 7.9 S. Challis · Structure no. 000000000017815

Built
1954
71 years old
Condition
Fair
inspected October 2024
Type
Tee Beam
Concrete Continuous
Length
320 ft
5 main spans
Daily traffic
1,100
2023 count
Owner
State
State Highway Agency

About this bridge

SH 75 over Salmon River is a concrete continuous tee beam carrying SH 75 over Salmon River in Custer County, Idaho. It was built in 1954, so it is 71 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 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 1,100 vehicles a day, roughly 15% of them trucks, projected to reach 1,650 by 2042. The structure is 320 ft (97.5 m) long and 32 ft wide. If it were closed, the detour would be 98.8 mi (159 km).

Location

Open in Google Maps
CarriesSH 75
CrossesSalmon River
Location7.9 S. Challis
RouteState Highway 75
CountyCuster County
StateIdaho
Coordinates44.40744, -114.25153
Functional classRural Minor Arterial

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.
Substructure5 FairAll primary structural elements are sound but may have minor section loss, cracking, spalling or scour.
Channel and channel protection7 GoodSome minor problems.
Last inspectionOctober 2024
Inspection intervalevery 24 months
Operating statusOpen, no restriction
ScourScour critical; foundations unstable for calculated scour conditions
Structural evaluation5: Somewhat better than minimum adequacy to tolerate being left in place as is
Deck geometry4: Meets minimum tolerable limits to be left in place as is
Waterway adequacy9: Superior to present desirable criteria
Approach roadway alignment8: Equal to present desirable criteria
Operating rating61 US tons
Inventory rating37 US tons

Structure

Structure typeTee Beam
MaterialConcrete Continuous
DeckConcrete, cast-in-place
Main spans5
Design loadHS 20
Structure length320 ft (97.5 m)
Longest span100 ft (30.5 m)
Deck width32 ft (9.7 m)
Roadway width26 ft (7.9 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic1,100 (2023)
Projected traffic1,650 by 2042
Trucks15%
Lanes on structure2
Traffic directionTwo-way traffic
CarriesHighway
CrossesWaterway
Detour if closed98.8 mi (159 km)
TollOn a free road
National Highway SystemNo

Ownership and planned work

OwnerState Highway Agency
Maintained byState Highway Agency
Historic statusHistorical significance not determinable at this time
Work proposedReplacement because of substandard load-carrying capacity or roadway geometry
Estimated improvement cost$3.5 million (2020 estimate)
NavigationNo navigation control on waterway

Frequently asked questions

When was SH 75 over Salmon River built?

It was built in 1954, making it 71 years old in 2025.

What condition is SH 75 over Salmon 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 October 2024.

How much traffic does SH 75 over Salmon River carry?

About 1,100 vehicles per day (2023 count), of which roughly 15% are trucks.

How long is SH 75 over Salmon River?

The structure is 320 ft (97.5 m) long with a longest span of 100 ft (30.5 m) and a deck 32 ft wide.

Who owns SH 75 over Salmon River?

It is owned by the State Highway Agency.