County profile · official public datasets

Bay County, MI

166 public highway bridges tracked in the FHWA National Bridge Inventory: 30.1% rated Good, 53% Fair, 16.9% Poor.

166
Public bridges: 30.1%
Good condition: 16.9%
Poor condition

The verdict

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

Bay County posts a higher-than-median Poor-condition share among rated counties in the state across mid-size county bridge inventory.

66th
of 83 on Poor share: 16.9%
Poor-condition share: 166
public highway bridges: 1974
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.

Bay County Bridge Snapshot

According to the Federal Highway Administration's 2024 National Bridge Inventory, Bay County ranks #66 of 83 Michigan counties with at least 5 public highway bridges on Poor-condition share (lower share ranks better; currently 16.9%). Bay County, Michigan contains 166 public highway bridges. Roughly 30.1% are rated “Good,” 53% “Fair,” and 16.9% “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.

Total bridges

166

Public highway bridges in Bay County

Good condition

30.1%

50 of 166 rated 7-9

Fair condition

53%

88 of 166 rated 5-6

Poor condition

16.9%

28 of 166 rated 4 or below

In-state Poor-share rank

#66 of 83

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

Condition distribution

Share of 166 NBI-tracked bridges by lowest applicable component rating.

Good

30.1% (50)

Fair

53% (88)

Poor

16.9% (28)

Bay County's Poor-condition bridges carry 64,301 vehicle crossings a day

That is 5.9% of the county's reported daily bridge traffic on 16.9% of its bridges: Poor-condition structures carry less traffic than their share of the inventory. Each Poor bridge averages 2,296 crossings a day against 8,156 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 166 of 166 bridges in this county that report an average daily traffic count. Source: FHWA National Bridge Inventory, 2024 release.

60.8% of Bay County's bridges have passed the 50-year mark

101 of the 166 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 30.1% 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 28.9% of the county's Poor-condition bridge traffic

I-75 NB over HESR, built 1960, carries 18,568 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 28-bridge count understates how much of the daily burden sits on a single crossing.

Share is of the 64,301 daily crossings on Poor-rated bridges that report a traffic count. Source: FHWA National Bridge Inventory, 2024 release.

1920s

3
1930s

18
1940s

5
1950s

16
1960s

47
1970s

18
1980s

11
1990s

14
2000s

13
2010s

13
2020s

8

What this shows Construction peaked in the 1960s, when 47 of the county's bridges still in the inventory were built, which is 28.3% of those with a recorded year. That cohort is now 55 to 64 years old in the 2024 inventory. Its average build year (1974) matches the Michigan average (1976).

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

The 5 Michigan counties nearest Bay County in number of bridges, with their condition splits. Its 16.9% Poor share is the 6th-lowest of these 6. Its average build year of 1974 against a peer-group mean of 1978 is in line with the group.

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

Bridge inventory size and condition shares for Bay County and the 5 Michigan counties closest to it in inventory size
County	Bridges	Good	Fair	Poor	Avg. built
Sanilac County	171	31.6%	58.5%	9.9%	1978
Gratiot County	167	40.7%	47.3%	12%	1975
Bay County (this page)	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 Bay 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 Bay County, both outside Michigan so the neighborhoods are not the same-state size table above.

Similar inventory size

Nearest county inventories outside MI (166 bridges here).

Clay County, IL · 166 bridges
Trego County, KS · 166 bridges
Pontotoc County, MS · 166 bridges
Barry County, MO · 166 bridges

Similar average build year

Nearest mean year-built outside MI (1974 here).

Knox County, TN · avg 1974 · 588 bridges
Summit County, OH · avg 1974 · 563 bridges
Onondaga County, NY · avg 1974 · 472 bridges
Orange County, NY · avg 1974 · 472 bridges

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

All 166 Good 50 Fair 88 Poor 28

Good-condition bridges (50)

Sort:

Bay County Bridge Snapshot

Condition distribution

Bay County's Poor-condition bridges carry 64,301 vehicle crossings a day

60.8% of Bay County's bridges have passed the 50-year mark

One structure carries 28.9% of the county's Poor-condition bridge traffic

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

Nationwide counties with similar inventory size or average build year

Similar inventory size

Similar average build year

Good-condition bridges (50)

ERICKSON ROAD

THREE MILE RD

PINCONNING ROAD

BEAVER ROAD

PINCONNING ROAD

ELEVEN MILE ROAD

NORTH UNION ROAD

11 MILE ROAD

FOUR MILE ROAD

TOWNLINE 16 ROAD

KAISER ROAD

PARISH ROAD

I-75 SB

I-75 SB

I-75 NB

WILDER RD

I-75 SB

I-75 NB

KINNEY ROAD

US-10 EB

US-10 WB & M-25 NB

M-13

M-47

WILDER RD

ELEVEN MILE ROAD

WHEELER RD

M-84

PINCONNING RD

I-75 NB

M-13

I-75 NB

I-75 SB

I-75 NB

TRUMAN PARKWAY

MIDLAND ROAD

WATER STREET

OLD BEAVER RD

MID-BAY CO LINE RD

TWO MILE ROAD

MACKINAW ROAD

GARFIELD ROAD

I-75

GARFIELD RD

MACKINAW RD

KAISER TOWER ROAD

GARFIELD ROAD

SEVEN MILE ROAD

M-84

I-75 SB

I-75 NB

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