County profile · official public datasets

Rock County, WI

304 public highway bridges tracked in the FHWA National Bridge Inventory: 61.2% rated Good, 35.2% Fair, 3.6% Poor.

304
Public bridges: 61.2%
Good condition: 3.6%
Poor condition

The verdict

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

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

Top 18%
lowest Poor share in state: 3.6%
Poor-condition share: 304
public highway bridges: 1994
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.

Rock County Bridge Snapshot

According to the Federal Highway Administration's 2024 National Bridge Inventory, Rock County ranks #13 of 72 Wisconsin counties with at least 5 public highway bridges on Poor-condition share (lower share ranks better; currently 3.6%). Rock County, Wisconsin contains 304 public highway bridges. Roughly 61.2% are rated “Good,” 35.2% “Fair,” and 3.6% “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

304

Public highway bridges in Rock County

Good condition

61.2%

186 of 304 rated 7-9

Fair condition

35.2%

107 of 304 rated 5-6

Poor condition

3.6%

11 of 304 rated 4 or below

In-state Poor-share rank

#13 of 72

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

Condition distribution

Share of 304 NBI-tracked bridges by lowest applicable component rating.

Good

61.2% (186)

Fair

35.2% (107)

Poor

3.6% (11)

Rock County's Poor-condition bridges carry 23,461 vehicle crossings a day

That is 1% of the county's reported daily bridge traffic on 3.6% of its bridges: Poor-condition structures carry less traffic than their share of the inventory. Each Poor bridge averages 2,133 crossings a day against 9,870 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 304 of 304 bridges in this county that report an average daily traffic count. Source: FHWA National Bridge Inventory, 2024 release.

18.1% of Rock County's bridges have passed the 50-year mark

55 of the 304 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 61.2% 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 62.2% of the county's Poor-condition bridge traffic

USH 51-CENTER AVE over CNW RR, built 1982, carries 14,600 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 11-bridge count understates how much of the daily burden sits on a single crossing.

Share is of the 23,461 daily crossings on Poor-rated bridges that report a traffic count. Source: FHWA National Bridge Inventory, 2024 release.

pre-1900

1
1910s

1
1920s

1
1930s

2
1940s

5
1950s

17
1960s

17
1970s

38
1980s

28
1990s

49
2000s

45
2010s

65
2020s

35

What this shows Construction peaked in the 2010s, when 65 of the county's bridges still in the inventory were built, which is 21.4% of those with a recorded year. That cohort is now 5 to 14 years old in the 2024 inventory. Its average build year is 1994, 10 years newer than the Wisconsin average of 1984.

How Rock County compares with Wisconsin's closest counties by inventory size

The 5 Wisconsin counties nearest Rock County in number of bridges, with their condition splits. Its 3.6% Poor share is the 2nd-lowest of these 6. Its average build year of 1994 against a peer-group mean of 1983 is 11 years newer.

Showing the 5 closest of 71 Wisconsin counties eligible for comparison.

Bridge inventory size and condition shares for Rock County and the 5 Wisconsin counties closest to it in inventory size
County	Bridges	Good	Fair	Poor	Avg. built
Barron County	319	48.6%	45.8%	5.6%	1978
Rock County (this page)	304	61.2%	35.2%	3.6%	1994
Richland County	298	54%	41.9%	4%	1986
St. Croix County	298	68.1%	28.9%	3%	1986
Clark County	296	54.4%	33.4%	12.2%	1983
Outagamie County	290	49.7%	46.2%	4.1%	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 Rock 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 Rock County, both outside Wisconsin so the neighborhoods are not the same-state size table above.

Similar inventory size

Nearest county inventories outside WI (304 bridges here).

Coles County, IL · 304 bridges
Knox County, IL · 304 bridges
Marshall County, IA · 304 bridges
Osage County, KS · 304 bridges

Similar average build year

Nearest mean year-built outside WI (1994 here).

Denton County, TX · avg 1994 · 991 bridges
St. Charles County, MO · avg 1994 · 417 bridges
Pitt County, NC · avg 1994 · 228 bridges
Columbus County, NC · avg 1994 · 226 bridges

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

All 304 Good 186 Fair 107 Poor 11

Good-condition bridges (186)

Sort:

Rock County Bridge Snapshot

Condition distribution

Rock County's Poor-condition bridges carry 23,461 vehicle crossings a day

18.1% of Rock County's bridges have passed the 50-year mark

One structure carries 62.2% of the county's Poor-condition bridge traffic

How Rock County compares with Wisconsin'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 (186)

LRD MARSH RD

LRD BELOIT-NEWARK

LRD ST LAWRENCE RD

LRD CRANSTON RD

STH 26 NB

STH 26 SB

LRD HAYNER RD

LRD SKINNER RD

IH 39 SB TO IH 43

LRD EMERALD GROVE

LRD 4TH ST

STH 59 EB

STH 59 WB

CTH S (SHOPIERE RD

STH 138

LRD RILEY RD

IH 39 NB/ IH 90 WB

STH 11 WB

STH 140

LRD JOHNSON DR

IH 39 SB / IH 90 E

IH 39 NB / IH 90 W

IH 43 SB

LRD SOUTH MAIN STR

STH 81-PORTLAND AV

STH EB STH 11

LRD CALEDONIA RD

STH 11

IH 39 SB / IH 90 E

IH 39 NB/90 WB

LRD DICKEY RD

LRD ORFORDVILLE-HA

CTH H

IH 39 SB / IH 90 E

IH 39 NB / IH 90 W

LRD EMERALD GROVE

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