County profile · official public datasets

Lyon County, IA

276 public highway bridges tracked in the FHWA National Bridge Inventory: 38.8% rated Good, 38.4% Fair, 22.8% Poor.

276
Public bridges: 38.8%
Good condition: 22.8%
Poor condition

The verdict

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

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

62nd
of 99 on Poor share: 22.8%
Poor-condition share: 276
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.

Lyon County Bridge Snapshot

According to the Federal Highway Administration's 2024 National Bridge Inventory, Lyon County ranks #62 of 99 Iowa counties with at least 5 public highway bridges on Poor-condition share (lower share ranks better; currently 22.8%). Lyon County, Iowa contains 276 public highway bridges. Roughly 38.8% are rated “Good,” 38.4% “Fair,” and 22.8% “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

276

Public highway bridges in Lyon County

Good condition

38.8%

107 of 276 rated 7-9

Fair condition

38.4%

106 of 276 rated 5-6

Poor condition

22.8%

63 of 276 rated 4 or below

In-state Poor-share rank

#62 of 99

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

Condition distribution

Share of 276 NBI-tracked bridges by lowest applicable component rating.

Good

38.8% (107)

Fair

38.4% (106)

Poor

22.8% (63)

Lyon County's Poor-condition bridges carry 14,300 vehicle crossings a day

That is 13.5% of the county's reported daily bridge traffic on 22.8% of its bridges: Poor-condition structures carry less traffic than their share of the inventory. Each Poor bridge averages 227 crossings a day against 198 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 276 of 276 bridges in this county that report an average daily traffic count. Source: FHWA National Bridge Inventory, 2024 release.

44.2% of Lyon County's bridges have passed the 50-year mark

122 of the 276 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 38.8% 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 7.1% of the county's Poor-condition bridge traffic

A26 (180TH ST) over BIG SIOUX RIVER, built 1977, carries 1,017 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 63-bridge count understates how much of the daily burden sits on a single crossing.

Share is of the 14,300 daily crossings on Poor-rated bridges that report a traffic count. Source: FHWA National Bridge Inventory, 2024 release.

1900s

44
1920s

1
1930s

1
1940s

5
1950s

14
1960s

31
1970s

56
1980s

21
1990s

19
2000s

20
2010s

54
2020s

10

What this shows Construction peaked in the 1970s, when 56 of the county's bridges still in the inventory were built, which is 20.3% of those with a recorded year. That cohort is now 45 to 54 years old in the 2024 inventory. Its average build year is 1974, 5 years older than the Iowa average of 1979.

How Lyon County compares with Iowa's closest counties by inventory size

The 5 Iowa counties nearest Lyon County in number of bridges, with their condition splits. Its 22.8% Poor share is the 6th-lowest of these 6. Its average build year of 1974 against a peer-group mean of 1983 is 9 years older.

Showing the 5 closest of 98 Iowa counties eligible for comparison.

Bridge inventory size and condition shares for Lyon County and the 5 Iowa counties closest to it in inventory size
County	Bridges	Good	Fair	Poor	Avg. built
Butler County	289	58.1%	26.6%	15.2%	1985
Lyon County (this page)	276	38.8%	38.4%	22.8%	1974
Kossuth County	267	44.6%	39%	16.5%	1987
Bremer County	266	51.9%	36.1%	12%	1990
Cerro Gordo County	266	44%	51.1%	4.9%	1975
O'Brien County	264	51.9%	43.2%	4.9%	1976

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

Similar inventory size

Nearest county inventories outside IA (276 bridges here).

Hardin County, OH · 276 bridges
Navajo County, AZ · 277 bridges
Delaware County, IN · 277 bridges
Porter County, IN · 277 bridges

Similar average build year

Nearest mean year-built outside IA (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 276 Good 107 Fair 106 Poor 63

Fair-condition bridges (106)

Sort:

Lyon County Bridge Snapshot

Condition distribution

Lyon County's Poor-condition bridges carry 14,300 vehicle crossings a day

44.2% of Lyon County's bridges have passed the 50-year mark

One structure carries 7.1% of the county's Poor-condition bridge traffic

How Lyon County compares with Iowa's closest counties by inventory size

Nationwide counties with similar inventory size or average build year

Similar inventory size

Similar average build year

Fair-condition bridges (106)

US 18

LOCAL ROAD

FM

FM

A50 (BRIDGE ST)

LOCAL ROAD

FM

FM

LOCAL ROAD

US 18

IBEX AVE

LOCAL ROAD

VIRGINIA ST

FM

LOCAL ROAD

FM

LOCAL ROAD

FM

FM

FM

IA 9

LOCAL

FM

FM

K60(INDIAN AVE)

LOCAL ROAD

LOCAL

FM

FM

LOCAL

LOCAL

FM

FM

LOCAL ROAD

LOCAL RD

FM

FM

FM

170TH ST

JEFFERSON ST

US 75 & IA 9

FM

FM

IA 9

US 18

FM

FM

FM

FM

IA 182

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