Structure 629 · Bay County, MI

I-75 SB over M-13 Conn

Carries I-75 SB over M-13 Conn, 2.5 Mi S Of Kawkawlin.

Overall conditionFair

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

How ratings work
Deck7/9 · Good
Superstructuresets the rating5/9 · Fair
Substructure7/9 · Good
0 failed4 poor6 fair9 excellent

Elevation

Side view, colored by inspection rating
SEMI-TRUCK · 72 FT160 FT OVERALL25 FT0ELEVATION · LENGTHS TO SCALE
Deck 7/9Superstructure 5/9 · sets the ratingSubstructure 7/9

160 ft end to end, longest span 68 ft: about 2 semi-trucks nose to tail. Lengths and the semi-truck 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.

Built196858 years old
Length159.8 ft48.7 m
Daily traffic11,225counted 2019
Last inspectedAugust 2024every 24 months

Location

StateMichigan
CountyBay
Location2.5 Mi S Of Kawkawlin
CarriesI-75 SB
CrossesM-13 Conn
Coordinates43.61863, -83.94879

Physical Characteristics

MaterialSteel
DesignStringer/Multi-beam
Total Length159.8 ft (48.7 m)
Max Span67.9 ft (20.7 m)
Deck Width42.0 ft (12.8 m)
Deck Area623.4 sq m
Main Spans3
Year Built1968

Traffic

Avg Daily Traffic11,225 (2019)
Truck Traffic9%
Lanes On Bridge2
Lanes Under Bridge2

Inspection & Ownership

Last InspectionAugust 2024
Inspection FrequencyEvery 24 months
OwnerState Highway Agency
Historical SignificanceBridge is not eligible for the National Register
Scour CriticalNot applicable
Structure Number000000000000629

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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