US Bridges

SH 21 over Mores Cr;thorn Creek

Good

Boise County, Idaho · 7.5 S. Idaho City · Structure no. 000000000012856

Built
2001
24 years old
Condition
Good
inspected October 2023
Type
Box Beam or Girders - Multiple
Prestressed Concrete
Length
82 ft
1 main span
Daily traffic
2,000
2023 count
Owner
State
State Highway Agency

About this bridge

SH 21 over Mores Cr;thorn Creek is a prestressed concrete box beam or girders - multiple carrying SH 21 over Mores Cr;thorn Creek in Boise County, Idaho. It was built in 2001, so it is 24 years old, younger than the Idaho average of 45.3 years.

The most recent inspection reported to the Federal Highway Administration rates it in good condition with a lowest component rating of 7 out of 9. All primary components (deck, superstructure, substructure, or culvert) are rated 7 or higher. No significant problems were noted.

It carries about 2,000 vehicles a day, roughly 18% of them trucks, projected to reach 3,000 by 2042. The structure is 82 ft (25 m) long and 40 ft wide. If it were closed, the detour would be 29.8 mi (48 km).

Location

Open in Google Maps
CarriesSH 21
CrossesMores Cr;thorn Creek
Location7.5 S. Idaho City
RouteState Highway 21
CountyBoise County
StateIdaho
Coordinates43.74683, -115.92314
Functional classRural Minor Arterial

Condition and inspection

Good

All primary components (deck, superstructure, substructure, or culvert) are rated 7 or higher. No significant problems were noted.

ComponentRatingMeaning
Deck7 GoodSome minor problems.
Superstructure8 Very GoodNo problems noted.
Substructure7 GoodSome minor problems.
Channel and channel protection8 Very GoodNo problems noted.
Last inspectionOctober 2023
Inspection intervalevery 48 months
Operating statusOpen, no restriction
ScourFoundations stable; scour above top of footing
Structural evaluation7: Better than present minimum criteria
Deck geometry6: Equal to present minimum criteria
Waterway adequacy6: Equal to present minimum criteria
Approach roadway alignment8: Equal to present desirable criteria
Operating rating91.1 US tons
Inventory rating55 US tons

Structure

Structure typeBox Beam or Girders - Multiple
MaterialPrestressed Concrete
DeckConcrete, cast-in-place
Main spans1
Design loadHS 25 or greater
Structure length82 ft (25 m)
Longest span79 ft (24.2 m)
Deck width40 ft (12.2 m)
Roadway width37 ft (11.4 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic2,000 (2023)
Projected traffic3,000 by 2042
Trucks18%
Lanes on structure2
Traffic directionTwo-way traffic
CarriesHighway
CrossesWaterway
Detour if closed29.8 mi (48 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 proposedNone recorded
Estimated improvement cost—
NavigationNo navigation control on waterway

Frequently asked questions

When was SH 21 over Mores Cr;thorn Creek built?

It was built in 2001, making it 24 years old in 2025.

What condition is SH 21 over Mores Cr;thorn Creek in?

The National Bridge Inventory rates it in good condition. All primary components (deck, superstructure, substructure, or culvert) are rated 7 or higher. No significant problems were noted. The last reported inspection was in October 2023.

How much traffic does SH 21 over Mores Cr;thorn Creek carry?

About 2,000 vehicles per day (2023 count), of which roughly 18% are trucks.

How long is SH 21 over Mores Cr;thorn Creek?

The structure is 82 ft (25 m) long with a longest span of 79 ft (24.2 m) and a deck 40 ft wide.

Who owns SH 21 over Mores Cr;thorn Creek?

It is owned by the State Highway Agency.