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

Good-condition bridges (88)

COLDWATER ROAD

Good

Over: SOUTH BR CHIPPEWA RIVER

0.2 M S NE COR SEC 35 T15, Isabella, MI

Built 1958 Load: 25.6 t ADT: 3,870

WEIDMAN ROAD

Good

Over: MCKAY DRAIN

0.3 MI W OF LOOMIS RD, Isabella, MI

Built 2015 Load: 28.5 t ADT: 196

BATTLE ROAD

Good

Over: N BR SALT RIVER

650 FT E LOOMIS ROAD, Isabella, MI

Built 2021 Load: 29.5 t ADT: 50

COE ROAD

Good

Over: LITTLE SALT RIVER

SEC 30-31 COE TWP, Isabella, MI

Built 1980 Load: 31.0 t ADT: 196

E COUNTY LINE ROAD

Good

Over: LITTLE SALT RIVER

SEC 1E COE TWP, Isabella, MI

Built 1983 Load: 31.0 t ADT: 196

SCHOOL ROAD

Good

Over: SOUTH BR CHIPPEWA RIVER

SEC 36C SHERMAN TWP, Isabella, MI

Built 1989 Load: 31.3 t ADT: 77

CHIPPEWA ROAD

Good

Over: POTTER CREEK

SEC 35-36 CHIPPEWA TWP, Isabella, MI

Built 1994 Load: 32.4 t ADT: 137

SUMMERTON ROAD

Good

Over: JORDAN CREEK

SEC 30W DENVER TWP, Isabella, MI

Built 1994 Load: 32.4 t ADT: 113

E COUNTY LINE ROAD

Good

Over: ONION CREEK

SEC 25 E CHIPPEWA TWP, Isabella, MI

Built 1990 Load: 32.6 t ADT: 336

SHEPHERD RD

Good

Over: CHILDS CREEK

SEC 16 & 17 COE TWP, Isabella, MI

Built 2007 Load: 32.6 t ADT: 1,742

BLANCHARD ROAD

Good

Over: BACHELDER DRAIN

SEC 12 FREMONT TWP, Isabella, MI

Built 1994 Load: 32.7 t ADT: 2,855

BASE LINE ROAD

Good

Over: JOHN NEFF DRAIN

50 FT E OF MISSION RD, Isabella, MI

Built 2009 Load: 32.7 t ADT: 427

ROSEBUSH ROAD

Good

Over: SPRING CREEK

0.3 M W NE COR SEC 14 T15, Isabella, MI

Built 1999 Load: 32.7 t ADT: 1,860

VERNON ROAD

Good

Over: WALKER CREEK

0.2M E SW COR SEC 35 T16N, Isabella, MI

Built 1995 Load: 32.7 t ADT: 120

WINN ROAD

Good

Over: CEDAR CREEK

100 FT S NW COR SEC 27 T1, Isabella, MI

Built 2003 Load: 32.7 t ADT: 1,650

DEERFIELD ROAD

Good

Over: POTTER CREEK

NW COR SEC 33 CHIPPEWA, Isabella, MI

Built 1993 Load: 32.7 t ADT: 1,930

WING ROAD

Good

Over: CEDAR CREEK

SEC 34C DEERFIELD TWP, Isabella, MI

Built 1992 Load: 32.7 t ADT: 137

SOUTH COUNTY LINE

Good

Over: CEDAR DRAIN

SEC 35 S FREMONT TWP, Isabella, MI

Built 2004 Load: 32.7 t ADT: 47

VANDECAR ROAD

Good

Over: THATCHER CREEK

SEC 26-27 FREMONT TWP, Isabella, MI

Built 1997 Load: 32.7 t ADT: 74

ISABELLA ROAD

Good

Over: SOUTH BR SALT RIVER

SEC 13-14 ISABELLA TWP, Isabella, MI

Built 2006 Load: 32.7 t ADT: 185

WALTON ROAD

Good

Over: PONY CREEK

ROLLAND TWP SEC 3/10, Isabella, MI

Built 2002 Load: 32.7 t ADT: 199

MISSION ROAD

Good

Over: LITTLE SALT RIVER

LINCOLN TWP SEC 22-23, Isabella, MI

Built 2003 Load: 32.7 t ADT: 150

LEATON ROAD

Good

Over: MCDONALD DRAIN

WISE TWP SEC 19-20, Isabella, MI

Built 2003 Load: 32.7 t ADT: 500

COLEMAN ROAD

Good

Over: CURTIS DRAIN

WISE TWP SEC 22, Isabella, MI

Built 2005 Load: 32.7 t ADT: 828

COLEMAN RD

Good

Over: LOOMIS DRAIN

600 W OF LOOMIS RD, Isabella, MI

Built 2009 Load: 32.7 t ADT: 1,145

VERNON ROAD

Good

Over: NORTH BR CHIPPEWA RIVER

0.3M W SE COR SEC 36 T16N, Isabella, MI

Built 1972 Load: 33.3 t ADT: 660

BASELINE ROAD

Good

Over: JOHN NEFF DRAIN

SEC 3 UNION TWP, Isabella, MI

Built 2004 Load: 33.3 t ADT: 144

WEIDMAN ROAD

Good

Over: LEWIS DRAIN

0.9 MI W OF MISSION ROAD, Isabella, MI

Built 2014 Load: 33.4 t ADT: 3,530

WINN ROAD

Good

Over: SOUTH BR CHIPPEWA RIVER

0.7 M S NE COR SEC 28 T14, Isabella, MI

Built 2002 Load: 34.7 t ADT: 3,408

WEIDMAN ROAD

Good

Over: LEWIS DRAIN

0.6 MI W OF MISSION ROAD, Isabella, MI

Built 2014 Load: 34.7 t ADT: 3,530

ISABELLA ROAD

Good

Over: LITTLE SALT RIVER

0.6 M S NE COR SEC 35 T13, Isabella, MI

Built 1993 Load: 34.8 t ADT: 686

REMICK ROAD

Good

Over: PINE RIVER

SEC 36C ROLLAND TWP, Isabella, MI

Built 1985 Load: 35.8 t ADT: 120

MISSION ROAD

Good

Over: ANN ARBOR RAILROAD

0.1M N SE COR SEC 27 T14N, Isabella, MI

Built 2005 Load: 37.8 t ADT: 9,200

COE RD

Good

Over: US-127

1.0 MI N OF GRATIOT COL, Isabella, MI

Built 1965 Load: 40.5 t ADT: 300

PLEASANT VALLEY RD

Good

Over: LITTLE SALT RIVER

SEC 16-21 COE TWP, Isabella, MI

Built 1989 Load: 41.3 t ADT: 511

ROSEBUSH ROAD

Good

Over: NORTH BR SALT RIVER

0.5M E NWCOR SEC15 DENV, Isabella, MI

Built 2017 Load: 42.1 t ADT: 885

SHEPHERD ROAD

Good

Over: POTTER CREEK

0.02M S NE COR SEC 32 T14, Isabella, MI

Built 1998 Load: 42.5 t ADT: 2,402

ISABELLA ROAD

Good

Over: SPRING CREEK

.28 M S NE COR SEC 14 T15, Isabella, MI

Built 1978 Load: 42.8 t ADT: 192

US-127 SB

Good

Over: US-10 BR

@ US-10, Isabella, MI

Built 2006 Load: 43.4 t ADT: 6,302

BROOMFIELD ROAD

Good

Over: ONION CREEK

SEC 23-26 CHIPPEWA TWP, Isabella, MI

Built 1992 Load: 43.6 t ADT: 236

BEAL CITY ROAD

Good

Over: JORDAN CREEK

0.5 MILE E OF LEATON RD, Isabella, MI

Built 1978 Load: 43.6 t ADT: 210

SHEPHERD ROAD

Good

Over: CHIPPEWA RIVER

.35 M S NE COR SEC 8 T14N, Isabella, MI

Built 1993 Load: 43.7 t ADT: 826

US-127 NB

Good

Over: US-10 BR

@ US-10, Isabella, MI

Built 2006 Load: 44.4 t ADT: 6,302

LOOMIS RD

Good

Over: N BR SALT RIVER

900 FT S OF BATTLE RD, Isabella, MI

Built 2021 Load: 44.4 t ADT: 423

WEIDMAN ROAD

Good

Over: LEWIS DRAIN

0.2 MI E OF MISSION ROAD, Isabella, MI

Built 2019 Load: 44.7 t ADT: 198

WEIDMAN ROAD

Good

Over: LEWIS DRAIN

0.1 MI E OF ISABELLA ROAD, Isabella, MI

Built 2014 Load: 44.7 t ADT: 196

M-20

Good

Over: CHIPPEWA RIVER

IN MT PLEASANT, Isabella, MI

Built 1996 Load: 45.0 t ADT: 10,842

WISE ROAD

Good

Over: LITTLE SALT RIVER

0.2 M N SE COR SEC 10 T13, Isabella, MI

Built 2010 Load: 47.2 t ADT: 1,548

JORDAN ROAD

Good

Over: COLDWATER RIVER

SEC 30-31 NOTTAWA TWP, Isabella, MI

Built 2013 Load: 47.3 t ADT: 614

BEAL CITY ROAD

Good

Over: NORTH BR CHIPPEWA RIVER

.15 M E NW COR SEC 25 T15, Isabella, MI

Built 2013 Load: 47.3 t ADT: 645

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.