Total bridges
171
Public highway bridges in Sanilac County
County profile · official public datasets
Sanilac County, MI
171 public highway bridges tracked in the FHWA National Bridge Inventory: 31.6% rated Good, 58.5% Fair, 9.9% Poor.
- 171
- Public bridges
- 31.6%
- Good condition
- 9.9%
- Poor condition
The verdict
According to the Federal Highway Administration's 2024 National Bridge Inventory.
Sanilac County posts a better-than-median Poor-condition share among rated counties in the state across mid-size county bridge inventory.
- Top 47%
- lowest Poor share in state
- 9.9%
- Poor-condition share
- 171
- public highway bridges
- 1978
- 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.
Sanilac County Bridge Snapshot
According to the Federal Highway Administration's 2024 National Bridge Inventory, Sanilac County ranks #39 of 83 Michigan counties with at least 5 public highway bridges on Poor-condition share (lower share ranks better; currently 9.9%). Sanilac County, Michigan contains 171 public highway bridges. Roughly 31.6% are rated “Good,” 58.5% “Fair,” and 9.9% “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
31.6%
54 of 171 rated 7-9
Fair condition
58.5%
100 of 171 rated 5-6
Poor condition
9.9%
17 of 171 rated 4 or below
In-state Poor-share rank
#39 of 83
Among Michigan counties with 5+ bridges, lower share ranks better
Condition distribution
Share of 171 NBI-tracked bridges by lowest applicable component rating.
Good 31.6% (54)
Fair 58.5% (100)
Poor 9.9% (17)
Sanilac County's Poor-condition bridges carry 20,523 vehicle crossings a day
That is 11.7% of the county's reported daily bridge traffic on 9.9% of its bridges: Poor-condition structures carry more traffic than their share of the inventory. Each Poor bridge averages 1,207 crossings a day against 1,529 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 171 of 171 bridges in this county that report an average daily traffic count. Source: FHWA National Bridge Inventory, 2024 release.
30.4% of Sanilac County's bridges have passed the 50-year mark
52 of the 171 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 31.6% 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 26.6% of the county's Poor-condition bridge traffic
M-46 over BLACK RIVER, built 1947, carries 5,462 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 17-bridge count understates how much of the daily burden sits on a single crossing.
Share is of the 20,523 daily crossings on Poor-rated bridges that report a traffic count. Source: FHWA National Bridge Inventory, 2024 release.
When Sanilac County's bridges were built
171 bridges with a recorded construction year, grouped by decade
- 1900s 2
1900–1909
2 bridges
- 1910s 1
1910–1919
1 bridges
- 1920s 3
1920–1929
3 bridges
- 1930s 15
1930–1939
15 bridges
- 1940s 5
1940–1949
5 bridges
- 1950s 9
1950–1959
9 bridges
- 1960s 7
1960–1969
7 bridges
- 1970s
1970–1979
21 bridges
- 1980s
1980–1989
52 bridges
- 1990s 19
1990–1999
19 bridges
- 2000s
2000–2009
28 bridges
- 2010s 6
2010–2019
6 bridges
- 2020s 3
2020–2029
3 bridges
What this shows Construction peaked in the 1980s, when 52 of the county's bridges still in the inventory were built, which is 30.4% of those with a recorded year. That cohort is now 35 to 44 years old in the 2024 inventory. Its average build year (1978) matches the Michigan average (1976).
How Sanilac County compares with Michigan's closest counties by inventory size
The 5 Michigan counties nearest Sanilac County in number of bridges, with their condition splits. Its 9.9% Poor share is the 3rd-lowest of these 6. Its average build year of 1978 against a peer-group mean of 1977 is in line with the group.
Showing the 5 closest of 82 Michigan counties eligible for comparison.
| County | Bridges | Good | Fair | Poor | Avg. built |
|---|---|---|---|---|---|
| Sanilac County (this page) | 171 | 31.6% | 58.5% | 9.9% | 1978 |
| Gratiot County | 167 | 40.7% | 47.3% | 12% | 1975 |
| Bay County | 166 | 30.1% | 53% | 16.9% | 1974 |
| Livingston County | 165 | 26.7% | 58.8% | 14.5% | 1974 |
| Lapeer County | 163 | 36.2% | 54.6% | 9.2% | 1982 |
| Shiawassee County | 163 | 45.4% | 45.4% | 9.2% | 1981 |
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 Sanilac 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 Sanilac County, both outside Michigan so the neighborhoods are not the same-state size table above.
Similar inventory size
Nearest county inventories outside MI (171 bridges here).
- Crenshaw County, AL · 171 bridges
- Miami County, IN · 171 bridges
- Lincoln County, LA · 171 bridges
- Pine County, MN · 171 bridges
Similar average build year
Nearest mean year-built outside MI (1978 here).
- Orange County, CA · avg 1978 · 1,164 bridges
- Sumner County, KS · avg 1978 · 659 bridges
- Allen County, IN · avg 1978 · 613 bridges
- Livingston County, IL · avg 1978 · 579 bridges
Source: FHWA National Bridge Inventory, 2024 release. Peers floor at 10 bridges so stub inventories cannot own the match.
All bridges (171)
PECK ROAD
GoodOver: ELK CREEK DRAIN
SEC 30-31 ELK TWP, Sanilac, MI
Built 2023 Load: 97.2 t ADT: 1,538
MARLETTE ROAD
GoodOver: POTTS DRAIN
SEC 31 WASHINGTON TWP, Sanilac, MI
Built 1996 Load: 97.2 t ADT: 840
FRENCH LINE ROAD
GoodOver: CARTER DRAIN
SEC 20-29 ELMER TWP, Sanilac, MI
Built 1994 Load: 97.2 t ADT: 314
FISHER RD
GoodOver: SANILAC & ST CLAIR DRAIN
SEC 34 SPEAKER TWP, Sanilac, MI
Built 2016 Load: 97.2 t ADT: 200
BAD AXE ROAD
PoorOver: S FORK OF N BR CASS RIV
SEC 18 AUSTIN TWP, Sanilac, MI
Built 1990 Load: 13.3 t ADT: 150
SANBORN STREET
PoorOver: BLACK RIVER
CITY OF CROSWELL, Sanilac, MI
Built 1974 Load: 15.6 t ADT: 850
MARLETTE ROAD
PoorOver: S BR CASS RIVER I/C DRN
SEC 36 MARLETTE TWP, Sanilac, MI
Built 1930 Load: 18.1 t ADT: 2,754
MUSHROOM ROAD
PoorOver: MIDDLE BR DRAIN
SEC 2-11 MOORE TWP, Sanilac, MI
Built 1984 Load: 18.1 t ADT: 150
SHELDEN ROAD
PoorOver: BRICE DRAIN
SEC 1-2 MOORE TWP, Sanilac, MI
Built 1930 Load: 23.7 t ADT: 150
RANGE LINE ROAD
PoorOver: FYE DRAIN
SEC 19 BRIDGEHAMPTON TWP, Sanilac, MI
Built 1982 Load: 25.9 t ADT: 225
SNOVER ROAD
PoorOver: MIDDLE BR DRAIN
SEC 14-23 MOORE TWP, Sanilac, MI
Built 1930 Load: 26.9 t ADT: 742
FREIBERGER ROAD
PoorOver: S FORK OF N BR CASS RIV
SEC 10-11 AUSTIN TWP, Sanilac, MI
Built 1985 Load: 31.1 t ADT: 160
CUSTER ROAD
PoorOver: BLACK RIVER I/C DRAIN
SEC 19-30 BRIDGEHAMPTON, Sanilac, MI
Built 1996 Load: 33.0 t ADT: 225
M-53
PoorOver: GREENMAN CREEK
5.8 MI S OF HURON CO LINE, Sanilac, MI
Built 1927 Load: 34.7 t ADT: 3,600
M-46
PoorOver: BLACK RIVER
5.6 MI E OF M-19, Sanilac, MI
Built 1947 Load: 34.7 t ADT: 5,462
GALBRAITH LINE RD
PoorOver: BLACK RIVER
SEC 20-29 WORTH TWP, Sanilac, MI
Built 1985 Load: 35.3 t ADT: 1,630
RICHMONDVILLE ROAD
PoorOver: BLACK RIVER I/C DRAIN
SEC 10-15 WHEATLAND TWP, Sanilac, MI
Built 1981 Load: 35.6 t ADT: 200
MOWERSON ROAD
PoorOver: ELK CREEK DRAIN
SEC 31 ELK TWP, Sanilac, MI
Built 1980 Load: 38.2 t ADT: 150
M-19
PoorOver: S FORK CASS RIVER
2.2 MI S OF HURON CO LINE, Sanilac, MI
Built 1957 Load: 43.4 t ADT: 1,600
BLACK RIVER ROAD
PoorOver: BLACK CREEK
SEC 17-18 WORTH TWP, Sanilac, MI
Built 1962 Load: 43.7 t ADT: 919
MARLETTE ROAD
PoorOver: BR #1 CARTER DRAIN
SEC 33 ELMER TWP, Sanilac, MI
Built 1984 Load: 97.2 t ADT: 1,556
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.