US Bridges

SH 21 over Mores Cr.;spencers Cabin

Good

Boise County, Idaho · 10.5 S. Idaho City · Structure no. 000000000012831

Built
1995
30 years old
Condition
Good
inspected October 2023
Type
Stringer/Multi-beam or Girder
Prestressed Concrete
Length
92 ft
1 main span
Daily traffic
2,900
2023 count
Owner
State
State Highway Agency

About this bridge

SH 21 over Mores Cr.;spencers Cabin is a prestressed concrete stringer/multi-beam or girder carrying SH 21 over Mores Cr.;spencers Cabin in Boise County, Idaho. It was built in 1995, so it is 30 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 2,900 vehicles a day, roughly 5% of them trucks, projected to reach 4,350 by 2042. The structure is 92 ft (28 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.;spencers Cabin
Location10.5 S. Idaho City
RouteState Highway 21
CountyBoise County
StateIdaho
Coordinates43.70722, -115.94808
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.
Superstructure7 GoodSome minor problems.
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 geometry5: Somewhat better than minimum adequacy to tolerate being left in place as is
Waterway adequacy8: Equal to present desirable criteria
Approach roadway alignment5: Somewhat better than minimum adequacy to tolerate being left in place as is
Operating rating88 US tons
Inventory rating53 US tons

Structure

Structure typeStringer/Multi-beam or Girder
MaterialPrestressed Concrete
DeckConcrete, cast-in-place
Main spans1
Design loadHS 25 or greater
Structure length92 ft (28 m)
Longest span90 ft (27.4 m)
Deck width40 ft (12.2 m)
Roadway width37 ft (11.4 m)
Vertical clearance over deckUnrestricted

Traffic and service

Average daily traffic2,900 (2023)
Projected traffic4,350 by 2042
Trucks5%
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.;spencers Cabin built?

It was built in 1995, making it 30 years old in 2025.

What condition is SH 21 over Mores Cr.;spencers Cabin 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.;spencers Cabin carry?

About 2,900 vehicles per day (2023 count), of which roughly 5% are trucks.

How long is SH 21 over Mores Cr.;spencers Cabin?

The structure is 92 ft (28 m) long with a longest span of 90 ft (27.4 m) and a deck 40 ft wide.

Who owns SH 21 over Mores Cr.;spencers Cabin?

It is owned by the State Highway Agency.