County profile · official public datasets

Isabella County, MI

183 public highway bridges tracked in the FHWA National Bridge Inventory: 48.1% rated Good, 38.8% Fair, 13.1% Poor.

183
Public bridges
48.1%
Good condition
13.1%
Poor condition

The verdict

According to the Federal Highway Administration's 2024 National Bridge Inventory.

Isabella County pairs a higher-than-median Poor-condition share among rated counties in the state with a newer average build year than the state inventory.

51st
of 83 on Poor share
13.1%
Poor-condition share
183
public highway bridges
1983
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.

Isabella County Bridge Snapshot

According to the Federal Highway Administration's 2024 National Bridge Inventory, Isabella County ranks #51 of 83 Michigan counties with at least 5 public highway bridges on Poor-condition share (lower share ranks better; currently 13.1%). Isabella County, Michigan contains 183 public highway bridges. Roughly 48.1% are rated “Good,” 38.8% “Fair,” and 13.1% “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.

Total bridges

183

Public highway bridges in Isabella County

Good condition

48.1%

88 of 183 rated 7-9

Fair condition

38.8%

71 of 183 rated 5-6

Poor condition

13.1%

24 of 183 rated 4 or below

In-state Poor-share rank

#51 of 83

Among Michigan counties with 5+ bridges, lower share ranks better

Condition distribution

Share of 183 NBI-tracked bridges by lowest applicable component rating.

Good
48.1% (88)
Fair
38.8% (71)
Poor
13.1% (24)

Isabella County's Poor-condition bridges carry 41,369 vehicle crossings a day

That is 12.1% of the county's reported daily bridge traffic on 13.2% of its bridges: Poor-condition structures carry less traffic than their share of the inventory. Each Poor bridge averages 1,724 crossings a day against 1,314 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 182 of 183 bridges in this county that report an average daily traffic count. Source: FHWA National Bridge Inventory, 2024 release.

42.6% of Isabella County's bridges have passed the 50-year mark

78 of the 183 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 48.1% 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 20.9% of the county's Poor-condition bridge traffic

US-127 NB over CHIPPEWA RIVER, built 1961, carries 8,658 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 24-bridge count understates how much of the daily burden sits on a single crossing.

Share is of the 41,369 daily crossings on Poor-rated bridges that report a traffic count. Source: FHWA National Bridge Inventory, 2024 release.

When Isabella County's bridges were built

183 bridges with a recorded construction year, grouped by decade

bridges

What this shows Construction peaked in the 1960s, when 45 of the county's bridges still in the inventory were built, which is 24.6% of those with a recorded year. That cohort is now 55 to 64 years old in the 2024 inventory. Its average build year is 1983, 7 years newer than the Michigan average of 1976.

Source FHWA National Bridge Inventory (year built) As of 2024 NBI release

How Isabella County compares with Michigan's closest counties by inventory size

The 5 Michigan counties nearest Isabella County in number of bridges, with their condition splits. Its 13.1% Poor share is the 5th-lowest of these 6. Its average build year of 1983 against a peer-group mean of 1976 is 7 years newer.

Showing the 5 closest of 82 Michigan counties eligible for comparison.

Bridge inventory size and condition shares for Isabella County and the 5 Michigan counties closest to it in inventory size
County Bridges Poor
Eaton County 200 6.5%
Huron County 192 6.3%
Isabella County (this page) 183 13.1%
Sanilac County 171 9.9%
Gratiot County 167 12%
Bay County 166 16.9%

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 Isabella 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 Isabella County, both outside Michigan so the neighborhoods are not the same-state size table above.

Similar inventory size

Nearest county inventories outside MI (183 bridges here).

Similar average build year

Nearest mean year-built outside MI (1983 here).

Source: FHWA National Bridge Inventory, 2024 release. Peers floor at 10 bridges so stub inventories cannot own the match.

All 183 Good 88 Fair 71 Poor 24

All bridges (183)

LOOMIS RD

Good

Over: MCKAY DRAIN

0.15 MI S OF WEIDMAN RD, Isabella, MI

Built 2022 Load: 61.9 t ADT: 50

ROLLAND ROAD

Good

Over: CHIPPEWA RIVER

SEC 27-28 SHERMAN TWP, Isabella, MI

Built 2019 Load: 62.2 t ADT: 284

SUMMERTON ROAD

Good

Over: LEWIS DRAIN

0.6 MI S OF WEIDMAN ROAD, Isabella, MI

Built 2014 Load: 62.9 t ADT: 185

LOOMIS ROAD

Good

Over: LOOMIS DRAIN

0.1 M S NE COR SEC 28 T16, Isabella, MI

Built 2010 Load: 64.7 t ADT: 654

TTP BIA 1011

Good

Over: ONION CREEK

SAGINAW CHIPPEWA RES., Isabella, MI

Built 2021 Load: 66.7 t

RIVER ROAD

Good

Over: NORTH BR CHIPPEWA RIVER

0.7 M W SE COR SEC 2 T14N, Isabella, MI

Built 2011 Load: 68.0 t ADT: 2,151

WOODRUFF ROAD

Good

Over: COLDWATER RIVER

0.2 M S NW COR SEC 7 T15N, Isabella, MI

Built 2010 Load: 76.2 t ADT: 1,189

WOODRUFF ROAD

Good

Over: COLDWATER RIVER

0.4 M N SW COR SEC 7 T15N, Isabella, MI

Built 2022 Load: 79.4 t ADT: 1,237

MISSION ROAD

Good

Over: NORTH BR CHIPPEWA RIVER

0.1 M S NE COR SEC 10 T14, Isabella, MI

Built 2008 Load: 87.0 t ADT: 9,019

US-127 SB

Poor

Over: EAST RIVER RD

0.1 MI N OF US-127 BR, Isabella, MI

Built 1961 Load: 0.0 t ADT: 8,625

WALTON ROAD

Poor

Over: LITTLE SALT RIVER

SEC 2-11 COE TWP, Isabella, MI

Built 1980 Load: 5.8 t ADT: 198

VERNON RD

Poor

Over: SHARPS CREEK

0.88 MI W OF N LOOMIS RD, Isabella, MI

Built 1969 Load: 6.5 t ADT: 85

E COUNTY LINE ROAD

Poor

Over: POTTER CREEK

0.1 M S NE COR SEC 36 T14, Isabella, MI

Built 1979 Load: 12.0 t ADT: 220

SHEPHERD RD

Poor

Over: SHARPS CREEK

50 FT N OF VERNON RD, Isabella, MI

Built 1969 Load: 12.3 t ADT: 85

DENVER ROAD

Poor

Over: NORTH BR SALT RIVER

SEC 4-9 DENVER TWP, Isabella, MI

Built 1937 Load: 15.1 t ADT: 185

SUMMERTON ROAD

Poor

Over: CONTRIB S BR SALT RIVER

SEC 18 W DENVER TWP, Isabella, MI

Built 1937 Load: 17.5 t ADT: 185

LOOMIS ROAD

Poor

Over: CHIPPEWA RIVER

.2 M S NW COR SEC 10 T14N, Isabella, MI

Built 1974 Load: 18.1 t ADT: 441

AIRLINE ROAD

Poor

Over: SOUTH BR CHIPPEWA RIVER

0.45M W NE COR SEC 17 T15, Isabella, MI

Built 1974 Load: 20.4 t ADT: 788

MILLBROOK ROAD

Poor

Over: PONY CREEK

0.4 M W SE COR SEC 35 T14, Isabella, MI

Built 1939 Load: 21.1 t ADT: 56

WYMAN ROAD

Poor

Over: SOUTH BR CHIPPEWA RIVER

SEC 20-21 SHERMAN TWP, Isabella, MI

Built 1941 Load: 22.8 t ADT: 233

DENVER ROAD

Poor

Over: NORTH BR CHIPPEWA RIVER

SEC 1-12 NOTTAWA TWP, Isabella, MI

Built 1937 Load: 22.9 t ADT: 123

ROSEBUSH ROAD

Poor

Over: NORTH BR SALT RIVER

0.1 M E NW COR SEC 14 DEN, Isabella, MI

Built 1971 Load: 24.5 t ADT: 1,740

MISSION ROAD

Poor

Over: SPRING CREEK

0.1M S NW COR SEC 11 T15N, Isabella, MI

Built 1935 Load: 28.2 t ADT: 5,200

MISSION ROAD

Poor

Over: LEWIS DRAIN

0.2M S NE COR SEC 22 T15N, Isabella, MI

Built 1930 Load: 28.8 t ADT: 6,140

WEIDMAN ROAD

Poor

Over: SPRING CREEK

SEC 17-20 DENVER TWP, Isabella, MI

Built 1981 Load: 29.8 t ADT: 196

VERNON RD

Poor

Over: US-127

6.1 MI S OF US-10, Isabella, MI

Built 1965 Load: 33.7 t ADT: 443

US-127 NB

Poor

Over: CHIPPEWA RIVER

1.9 MI NW OF M-20, Isabella, MI

Built 1961 Load: 34.7 t ADT: 8,658

WEIDMAN ROAD

Poor

Over: COLDWATER RIVER

0.1 M E SW COR SEC 18 T15, Isabella, MI

Built 1966 Load: 39.9 t ADT: 3,604

US-127 BR NB

Poor

Over: US-127 SB

@ US-127 BR, Isabella, MI

Built 1961 Load: 41.1 t ADT: 2,953

BECKLEY ROAD

Poor

Over: PINE RIVER

SEC 23C ROLLAND TWP, Isabella, MI

Built 1969 Load: 46.4 t ADT: 121

BASELINE ROAD

Poor

Over: COLDWATER RIVER

.35 M W SE COR SEC 31 T15, Isabella, MI

Built 1903 Load: 50.3 t ADT: 192

LEATON ROAD

Poor

Over: JORDAN CREEK

0.37 MI S BEAL CITY ROAD, Isabella, MI

Built 1970 Load: 53.1 t ADT: 100

ROSEBUSH ROAD

Poor

Over: NORTH BRANCH SALT RIVER

0.4 MI W OF LOOMIS ROAD, Isabella, MI

Built 1966 Load: 63.5 t ADT: 798

Read our methodology - how this data is sourced, computed, and verified.

Related

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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.