US Bridges

W Blackrock Road over Portneuf R;nw.Inkom Br

Fair

Bannock County, Idaho · 0.2 N. 4.0 W. Inkom · Structure no. 000000000021940

Built
1948
77 years old
Condition
Fair
inspected September 2024
Type
Culvert
Steel
Length
42 ft
2 main spans
Daily traffic
100
2023 count
Owner
County
County Highway Agency

About this bridge

W Blackrock Road over Portneuf R;nw.Inkom Br is a steel culvert carrying W Blackrock Road over Portneuf R;nw.Inkom Br in Bannock County, Idaho. It was built in 1948, so it is 77 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 100 vehicles a day, roughly 10% of them trucks, projected to reach 150 by 2039. The structure is 42 ft (12.8 m) long and 31 ft wide. If it were closed, the detour would be 3.7 mi (6 km).

Location

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CarriesW Blackrock Road
CrossesPortneuf R;nw.Inkom Br
Location0.2 N. 4.0 W. Inkom
RouteCounty Highway 0
CountyBannock County
StateIdaho
Coordinates42.79519, -112.32942
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
Channel and channel protection6 SatisfactoryStructural elements show some minor deterioration.
Culvert6 SatisfactoryStructural elements show some minor deterioration.
Last inspectionSeptember 2024
Inspection intervalevery 48 months
Operating statusOpen, no restriction
ScourFoundations stable; scour above top of footing
Structural evaluation6: Equal to present minimum criteria
Deck geometry6: Equal to present minimum criteria
Waterway adequacy7: Better than present minimum criteria
Approach roadway alignment8: Equal to present desirable criteria
Operating rating54.6 US tons
Inventory rating35.7 US tons

Structure

Structure typeCulvert
MaterialSteel
DeckNot applicable
Main spans2
Design loadHS 20
Structure length42 ft (12.8 m)
Longest span20 ft (6.1 m)
Deck width31 ft (9.4 m)
Roadway width25 ft (7.5 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic100 (2023)
Projected traffic150 by 2039
Trucks10%
Lanes on structure2
Traffic directionTwo-way traffic
CarriesHighway
CrossesWaterway
Detour if closed3.7 mi (6 km)
TollOn a free road
National Highway SystemNo

Ownership and planned work

OwnerCounty Highway Agency
Maintained byCounty 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 W Blackrock Road over Portneuf R;nw.Inkom Br built?

It was built in 1948, making it 77 years old in 2025.

What condition is W Blackrock Road over Portneuf R;nw.Inkom Br 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 September 2024.

How much traffic does W Blackrock Road over Portneuf R;nw.Inkom Br carry?

About 100 vehicles per day (2023 count), of which roughly 10% are trucks.

How long is W Blackrock Road over Portneuf R;nw.Inkom Br?

The structure is 42 ft (12.8 m) long with a longest span of 20 ft (6.1 m) and a deck 31 ft wide.

Who owns W Blackrock Road over Portneuf R;nw.Inkom Br?

It is owned by the County Highway Agency.