Structure 12835 · Boise County, ID

SH 21 over Mores Cr.;grimes Cr.road

Carries SH 21 over Mores Cr.;grimes Cr.road, 9.5 S. Idaho City.

Overall conditionFair

Set by its lowest-rated component: Deck at 5 of 9.

How ratings work
Decksets the rating5/9 · Fair
Superstructure6/9 · Satisfactory
Substructure6/9 · Satisfactory
Channelnot part of overall6/9 · Satisfactory
0 failed4 poor6 fair9 excellent

Elevation

Side view, colored by inspection rating
CAR · 15 FT40 FT OVERALL25 FT0ELEVATION · LENGTHS TO SCALE
Deck 5/9 · sets the ratingSuperstructure 6/9Substructure 6/9

40 ft end to end. Lengths and the car on the deck are drawn to the same scale. Each part is colored by its latest inspection rating. The inventory records lengths but not heights or the layout of the shorter spans, so those are drawn as typical for a multi-beam bridge.

Built195868 years old
Length40.0 ft12.2 m
Daily traffic2,900counted 2023
Last inspectedOctober 2023every 24 months

Location

StateIdaho
CountyBoise
Location9.5 S. Idaho City
CarriesSH 21
CrossesMores Cr.;grimes Cr.road
Coordinates43.72567, -115.95147

Physical Characteristics

MaterialConcrete
DesignStringer/Multi-beam
Total Length40.0 ft (12.2 m)
Max Span38.7 ft (11.8 m)
Deck Width36.1 ft (11 m)
Deck Area134.2 sq m
Main Spans1
Year Built1958

Traffic

Avg Daily Traffic2,900 (2023)
Truck Traffic5%
Lanes On Bridge2

Inspection & Ownership

Last InspectionOctober 2023
Inspection FrequencyEvery 24 months
OwnerState Highway Agency
Historical SignificanceHistorical significance is not determined
Scour Critical5 — Stable for scour
Structure Number000000000012835

How Bridge Ratings Work

Inspectors rate each major part of a bridge (the deck you drive on, the superstructure of beams that holds it up, and the substructure of piers and abutments beneath) on a 0–9 scale. A bridge's overall condition is its lowest of those ratings, so one deteriorated component makes the whole bridge "poor."

0Failed
1Imminent failure
2Critical
3Serious
4Poor
5Fair
6Satisfactory
7Good
8Very good
9Excellent
Good · lowest component 7–9
Fair · lowest component 5–6
Poor · lowest component 0–4

A poor rating is not a closure. It means the bridge is flagged for priority repair or replacement; bridges judged unsafe are closed or posted with weight limits. The waterway (channel) rating is reported, but it does not count toward the overall classification.

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