US Bridges

SH 21 over Clear Creek;at Lowman

Fair

Boise County, Idaho · At Lowman · Structure no. 000000000012890

Built
1939
86 years old
Condition
Fair
inspected October 2024
Type
Stringer/Multi-beam or Girder
Steel Continuous
Length
150 ft
3 main spans
Daily traffic
1,200
2023 count
Owner
State
State Highway Agency

About this bridge

SH 21 over Clear Creek;at Lowman is a steel continuous stringer/multi-beam or girder carrying SH 21 over Clear Creek;at Lowman in Boise County, Idaho. It was built in 1939, so it is 86 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 1,200 vehicles a day, roughly 9% of them trucks, projected to reach 1,800 by 2042. The structure is 150 ft (45.7 m) long and 31 ft wide. If it were closed, the detour would be 98.8 mi (159 km).

Location

Open in Google Maps
CarriesSH 21
CrossesClear Creek;at Lowman
LocationAt Lowman
RouteState Highway 21
CountyBoise County
StateIdaho
Coordinates44.08248, -115.61271
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 protection8 Very GoodNo problems noted.
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 adequacy8: Equal to present desirable criteria
Approach roadway alignment8: Equal to present desirable criteria
Operating rating46 US tons
Inventory rating27 US tons

Structure

Structure typeStringer/Multi-beam or Girder
MaterialSteel Continuous
DeckConcrete, cast-in-place
Main spans3
Design loadH 15
Structure length150 ft (45.7 m)
Longest span60 ft (18.3 m)
Deck width31 ft (9.4 m)
Roadway width24 ft (7.3 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic1,200 (2023)
Projected traffic1,800 by 2042
Trucks9%
Lanes on structure2
Traffic directionTwo-way traffic
CarriesHighway and pedestrian
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$2.4 million (2020 estimate)
NavigationNo navigation control on waterway

Frequently asked questions

When was SH 21 over Clear Creek;at Lowman built?

It was built in 1939, making it 86 years old in 2025.

What condition is SH 21 over Clear Creek;at Lowman 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 21 over Clear Creek;at Lowman carry?

About 1,200 vehicles per day (2023 count), of which roughly 9% are trucks.

How long is SH 21 over Clear Creek;at Lowman?

The structure is 150 ft (45.7 m) long with a longest span of 60 ft (18.3 m) and a deck 31 ft wide.

Who owns SH 21 over Clear Creek;at Lowman?

It is owned by the State Highway Agency.