County profile · official public datasets

Polk County, IA

545 public highway bridges tracked in the FHWA National Bridge Inventory: 57.8% rated Good, 35.8% Fair, 6.4% Poor.

545
Public bridges: 57.8%
Good condition: 6.4%
Poor condition

The verdict

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

Polk County pairs a top-10% lowest Poor-condition share among rated counties in the state with a newer average build year than the state inventory.

Top 7%
lowest Poor share in state: 6.4%
Poor-condition share: 545
public highway bridges: 1986
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.

Polk County Bridge Snapshot

According to the Federal Highway Administration's 2024 National Bridge Inventory, Polk County ranks #7 of 99 Iowa counties with at least 5 public highway bridges on Poor-condition share (lower share ranks better; currently 6.4%). Polk County, Iowa contains 545 public highway bridges. Roughly 57.8% are rated “Good,” 35.8% “Fair,” and 6.4% “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

545

Public highway bridges in Polk County

Good condition

57.8%

315 of 545 rated 7-9

Fair condition

35.8%

195 of 545 rated 5-6

Poor condition

6.4%

35 of 545 rated 4 or below

In-state Poor-share rank

#7 of 99

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

Condition distribution

Share of 545 NBI-tracked bridges by lowest applicable component rating.

Good

57.8% (315)

Fair

35.8% (195)

Poor

6.4% (35)

Polk County's Poor-condition bridges carry 81,796 vehicle crossings a day

That is 1.2% of the county's reported daily bridge traffic on 6.3% of its bridges: Poor-condition structures carry less traffic than their share of the inventory. Each Poor bridge averages 2,406 crossings a day against 11,988 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 542 of 545 bridges in this county that report an average daily traffic count. Source: FHWA National Bridge Inventory, 2024 release.

29.9% of Polk County's bridges have passed the 50-year mark

163 of the 545 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 57.8% 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 19.1% of the county's Poor-condition bridge traffic

FLEUR DR over OLD UP RR & SW 22ND, built 1936, carries 15,634 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 35-bridge count understates how much of the daily burden sits on a single crossing.

Share is of the 81,796 daily crossings on Poor-rated bridges that report a traffic count. Source: FHWA National Bridge Inventory, 2024 release.

1900s

4
1910s

8
1920s

9
1930s

14
1940s

5
1950s

43
1960s

58
1970s

44
1980s

39
1990s

103
2000s

142
2010s

64
2020s

12

What this shows Construction peaked in the 2000s, when 142 of the county's bridges still in the inventory were built, which is 26.1% of those with a recorded year. That cohort is now 15 to 24 years old in the 2024 inventory. Its average build year is 1986, 7 years newer than the Iowa average of 1979.

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

The 5 Iowa counties nearest Polk County in number of bridges, with their condition splits. Its 6.4% Poor share is the 3rd-lowest of these 6. Its average build year of 1986 against a peer-group mean of 1984 is in line with the group.

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

Bridge inventory size and condition shares for Polk County and the 5 Iowa counties closest to it in inventory size
County	Bridges	Good	Fair	Poor	Avg. built
Pottawattamie County	557	38.8%	51.9%	9.3%	1981
Polk County (this page)	545	57.8%	35.8%	6.4%	1986
Linn County	506	46.4%	47.2%	6.3%	1987
Black Hawk County	489	52.8%	40.7%	6.5%	1983
Woodbury County	455	39.3%	39.6%	21.1%	1985
Sioux County	449	62.4%	34.7%	2.9%	1982

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

Similar inventory size

Nearest county inventories outside IA (545 bridges here).

Grafton County, NH · 544 bridges
Yavapai County, AZ · 543 bridges
East Baton Rouge County, LA · 548 bridges
Kanawha County, WV · 554 bridges

Similar average build year

Nearest mean year-built outside IA (1986 here).

El Paso County, TX · avg 1986 · 783 bridges
Caddo County, LA · avg 1986 · 682 bridges
Weld County, CO · avg 1986 · 614 bridges
Canadian County, OK · avg 1986 · 493 bridges

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

All 545 Good 315 Fair 195 Poor 35

All bridges (545)

Sort:

Polk County Bridge Snapshot

Condition distribution

Polk County's Poor-condition bridges carry 81,796 vehicle crossings a day

29.9% of Polk County's bridges have passed the 50-year mark

One structure carries 19.1% of the county's Poor-condition bridge traffic

How Polk 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

All bridges (545)

NB I 35 EB I 80

I 80 WB I 35 SB

NW 72ND PLACE

SBI35 TO EBI80

NB I-35 EB I-80

WB IA 141

S.W.3RD ST

EBI235 TO WBI80

UNI AVE WB ENTR

73RD ST

28TH ST

FM

E MLK JR PKWY

E MLK JR PKWY

MLK EB

MLK WB

W UNIVERSITY

LOCAL ROAD

GRAND AVE

E 14TH ST-US 69 SB

LOCAL ROAD

FM

WB I-235

SW 9TH ST

2ND AVE EB RAMP

EB I-235

MLK JR PKWY E/W

MLK JR PKWY N

MLK JR PKWY S

NB US 65

NB US 65

EB I-235

LOCAL

FM

FM

WB I-235

I 35 NB I 80 EB

SB I-35 WB I-80

SE 6TH AVE

NB I-35 EB I-80

UNIVERSITY AVE

OLD IA 950 FM

NB(WB) POLK BLV

32ND ST SE

SB US 65

E 15TH RAMP D

I-235 WB

60TH ST

I 235 EB

I 235 EB OFF RAMP

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