Total bridges
327
Public highway bridges in St. Clair County
County profile · official public datasets
St. Clair County, MI
327 public highway bridges tracked in the FHWA National Bridge Inventory: 41.3% rated Good, 50.5% Fair, 8.3% Poor.
- 327
- Public bridges
- 41.3%
- Good condition
- 8.3%
- Poor condition
The verdict
According to the Federal Highway Administration's 2024 National Bridge Inventory.
St. Clair County pairs a better-than-median Poor-condition share among rated counties in the state with a newer average build year than the state inventory.
- Top 39%
- lowest Poor share in state
- 8.3%
- Poor-condition share
- 327
- public highway bridges
- 1985
- avg year built
Poor is an FHWA condition category from the lowest applicable component rating (4 or below), not a live crossing-safety or closure decision. Rankings cover counties with at least five public highway bridges.
St. Clair County Bridge Snapshot
According to the Federal Highway Administration's 2024 National Bridge Inventory, St. Clair County ranks #32 of 83 Michigan counties with at least 5 public highway bridges on Poor-condition share (lower share ranks better; currently 8.3%). St. Clair County, Michigan contains 327 public highway bridges. Roughly 41.3% are rated “Good,” 50.5% “Fair,” and 8.3% “Poor.” Poor means the lowest applicable deck, superstructure, substructure, or culvert rating is 4 or below on the 0–9 NBI scale. It is a condition category, not a live safety or closure decision.
Responsible agencies inspect covered bridges on risk-based intervals under current NBIS rules and submit inventory data to FHWA annually. The list below shows every NBI-tracked bridge in the county. Use the “Sort by” controls to change the ordering, and click any row for its reported inspection date, traffic count, and condition fields.
Source: FHWA National Bridge Inventory. See methodology for full definitions.
Good condition
41.3%
135 of 327 rated 7-9
Fair condition
50.5%
165 of 327 rated 5-6
Poor condition
8.3%
27 of 327 rated 4 or below
In-state Poor-share rank
#32 of 83
Among Michigan counties with 5+ bridges, lower share ranks better
Condition distribution
Share of 327 NBI-tracked bridges by lowest applicable component rating.
Good 41.3% (135)
Fair 50.5% (165)
Poor 8.3% (27)
St. Clair County's Poor-condition bridges carry 38,796 vehicle crossings a day
That is 3% of the county's reported daily bridge traffic on 8.3% of its bridges: Poor-condition structures carry less traffic than their share of the inventory. Each Poor bridge averages 1,437 crossings a day against 4,382 for a Good-condition one. A Poor rating is a condition category, not a closure or a live safety judgement; it means the lowest applicable component rating is 4 or below.
Computed over the 326 of 327 bridges in this county that report an average daily traffic count. Source: FHWA National Bridge Inventory, 2024 release.
26.9% of St. Clair County's bridges have passed the 50-year mark
88 of the 327 bridges with a recorded construction year were built in 1974 or earlier. Age alone is not a defect: a well-maintained older bridge can rate Good, and 41.3% of this county's inventory does. Even so, this older cohort is the population from which future Poor ratings are drawn, which is why the age profile below matters alongside the condition split above.
Cutoff derives from the 2024 release year minus a 50-year design life. Source: FHWA National Bridge Inventory, 2024 release.
One structure carries 55.7% of the county's Poor-condition bridge traffic
I-94 WB over M-25 CONN, built 1964, carries 21,619 vehicles a day, the most of any Poor-rated structure here. The county's Poor-condition exposure is concentrated rather than evenly spread, so the 27-bridge count understates how much of the daily burden sits on a single crossing.
Share is of the 38,796 daily crossings on Poor-rated bridges that report a traffic count. Source: FHWA National Bridge Inventory, 2024 release.
When St. Clair County's bridges were built
327 bridges with a recorded construction year, grouped by decade
- 1910s 2
1910–1919
2 bridges
- 1920s 9
1920–1929
9 bridges
- 1930s 17
1930–1939
17 bridges
- 1940s 14
1940–1949
14 bridges
- 1950s 8
1950–1959
8 bridges
- 1960s
1960–1969
31 bridges
- 1970s 25
1970–1979
25 bridges
- 1980s
1980–1989
77 bridges
- 1990s
1990–1999
34 bridges
- 2000s 28
2000–2009
28 bridges
- 2010s
2010–2019
69 bridges
- 2020s 13
2020–2029
13 bridges
What this shows Construction peaked in the 1980s, when 77 of the county's bridges still in the inventory were built, which is 23.5% of those with a recorded year. That cohort is now 35 to 44 years old in the 2024 inventory. Its average build year is 1985, 9 years newer than the Michigan average of 1976.
How St. Clair County compares with Michigan's closest counties by inventory size
The 5 Michigan counties nearest St. Clair County in number of bridges, with their condition splits. Its 8.3% Poor share is the 2nd-lowest of these 6. Its average build year of 1985 against a peer-group mean of 1975 is 10 years newer.
Showing the 5 closest of 82 Michigan counties eligible for comparison.
| County | Bridges | Good | Fair | Poor | Avg. built |
|---|---|---|---|---|---|
| Genesee County | 371 | 22.9% | 61.7% | 15.4% | 1968 |
| St. Clair County (this page) | 327 | 41.3% | 50.5% | 8.3% | 1985 |
| Saginaw County | 315 | 28.9% | 52.7% | 18.4% | 1979 |
| Monroe County | 297 | 30% | 54.5% | 15.5% | 1974 |
| Berrien County | 272 | 27.6% | 66.5% | 5.9% | 1979 |
| Washtenaw County | 262 | 23.3% | 56.5% | 20.2% | 1975 |
Each share is of that county's own total tracked bridges; peers are the counties with 5 or more bridges whose inventory size is closest to St. Clair County's. Source: FHWA National Bridge Inventory, 2024 release.
Nationwide counties with similar inventory size or average build year
Two NBI-derived peer sets for St. Clair County, both outside Michigan so the neighborhoods are not the same-state size table above.
Similar inventory size
Nearest county inventories outside MI (327 bridges here).
- Henry County, IL · 328 bridges
- Nassau County, NY · 328 bridges
- Miami County, KS · 326 bridges
- Montgomery County, KS · 326 bridges
Similar average build year
Nearest mean year-built outside MI (1985 here).
- Hillsborough County, FL · avg 1985 · 840 bridges
- Lancaster County, NE · avg 1985 · 661 bridges
- Nueces County, TX · avg 1985 · 528 bridges
- Grayson County, TX · avg 1985 · 513 bridges
Source: FHWA National Bridge Inventory, 2024 release. Peers floor at 10 bridges so stub inventories cannot own the match.
Fair-condition bridges (165)
RILEY CENTER RD
FairOver: I-69
7.0 MI SE OF CAPAC, St. Clair, MI
Built 1982 Load: 56.1 t ADT: 1,030
METCALF ROAD
FairOver: GALBRAITH DRAIN
SEC. 31 BURTCHVILLE TWP., St. Clair, MI
Built 1985 Load: 56.1 t ADT: 165
PHELPS ROAD
FairOver: SWARTOUT DRAIN
PC 198-309 CLAY TWP, St. Clair, MI
Built 1996 Load: 56.1 t ADT: 465
M-19
FairOver: COWHY DRAIN
N END OF M-19/I-69 INTRCH, St. Clair, MI
Built 1981 Load: 56.1 t ADT: 6,607
I-94 EB
FairOver: GTW RR
0.6 MI W OF M-21, St. Clair, MI
Built 2003 Load: 56.7 t ADT: 14,887
LAPEER RD (M-21)
FairOver: COWHEY CR
1.3 MI E OF M-19, St. Clair, MI
Built 1953 Load: 58.3 t ADT: 2,514
BRIDGE STREET
FairOver: BELLE RIVER
BRIDGE ST S OF MAIN ST, St. Clair, MI
Built 2013 Load: 60.9 t ADT: 11,000
COMSTOCK ROAD
FairOver: BLACK RIVER
SEC 17 GRANT TWP, St. Clair, MI
Built 1996 Load: 61.6 t ADT: 1,025
STERLING ROAD
FairOver: S. BR. MILL CREEK DRAIN
SEC. 23 LYNN TWP., St. Clair, MI
Built 1985 Load: 68.7 t ADT: 1,110
JEDDO ROAD
FairOver: BURTCH CREEK
SEC. 6-7 BURCTHVILLE TWP., St. Clair, MI
Built 1957 Load: 69.0 t ADT: 450
INDIAN TRAIL ROAD
FairOver: BELLE RIVER
SEC 15 CHINA TWP, St. Clair, MI
Built 2007 Load: 82.3 t ADT: 2,104
I-94
FairOver: STOCKS CREEK
430 FT N OF LAPEER RD, St. Clair, MI
Built 1964 Load: 97.2 t ADT: 29,650
MARINE CITY HWY
FairOver: BEAUBIEN CREEK DRAIN
SEC. 32 CHINA TWP., St. Clair, MI
Built 1946 Load: 97.2 t ADT: 8,050
COVE ROAD
FairOver: UNNAMED CREEK
SEC. 17 WALES TWP., St. Clair, MI
Built 1921 Load: 97.2 t ADT: 188
DOVE ROAD
FairOver: UNNAMED CREEK
SEC. 15-22 KIMBALL TWP., St. Clair, MI
Built 1962 Load: 97.2 t ADT: 752
Read our methodology - how this data is sourced, computed, and verified.
Related
Data sourced from official public datasets. See our methodology for details. Retrieved and formatted by PlainBridges
Every figure on PlainBridges is rendered directly from federal source data, no number is typed in by an editor. This page draws directly on federal source data, no figure is typed in by an editor. See our editorial standards & corrections policy, the methodology behind these numbers, or report a data error. NBI condition categories reflect the latest reported inventory record, not a live safety, closure, or travel decision.