County profile · official public datasets

Humboldt County, CA

396 public highway bridges tracked in the FHWA National Bridge Inventory: 38.9% rated Good, 54.3% Fair, 6.8% Poor.

396
Public bridges: 38.9%
Good condition: 6.8%
Poor condition

The verdict

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

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

Top 50%
lowest Poor share in state: 6.8%
Poor-condition share: 396
public highway bridges: 1968
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.

Humboldt County Bridge Snapshot

According to the Federal Highway Administration's 2024 National Bridge Inventory, Humboldt County ranks #29 of 58 California counties with at least 5 public highway bridges on Poor-condition share (lower share ranks better; currently 6.8%). Humboldt County, California contains 396 public highway bridges. Roughly 38.9% are rated “Good,” 54.3% “Fair,” and 6.8% “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

396

Public highway bridges in Humboldt County

Good condition

38.9%

154 of 396 rated 7-9

Fair condition

54.3%

215 of 396 rated 5-6

Poor condition

6.8%

27 of 396 rated 4 or below

In-state Poor-share rank

#29 of 58

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

Condition distribution

Share of 396 NBI-tracked bridges by lowest applicable component rating.

Good

38.9% (154)

Fair

54.3% (215)

Poor

6.8% (27)

Humboldt County's Poor-condition bridges carry 42,605 vehicle crossings a day

That is 3% of the county's reported daily bridge traffic on 6.8% of its bridges: Poor-condition structures carry less traffic than their share of the inventory. Each Poor bridge averages 1,578 crossings a day against 4,152 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 396 of 396 bridges in this county that report an average daily traffic count. Source: FHWA National Bridge Inventory, 2024 release.

69.2% of Humboldt County's bridges have passed the 50-year mark

274 of the 396 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 38.9% 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 41.1% of the county's Poor-condition bridge traffic

US HIGHWAY 101 NB over WEST END RD CREEK NCRRA, built 1929, carries 17,500 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 27-bridge count understates how much of the daily burden sits on a single crossing.

Share is of the 42,605 daily crossings on Poor-rated bridges that report a traffic count. Source: FHWA National Bridge Inventory, 2024 release.

1910s

3
1920s

16
1930s

17
1940s

13
1950s

63
1960s

135
1970s

52
1980s

46
1990s

25
2000s

9
2010s

13
2020s

4

What this shows Construction peaked in the 1960s, when 135 of the county's bridges still in the inventory were built, which is 34.1% of those with a recorded year. That cohort is now 55 to 64 years old in the 2024 inventory. Its average build year (1968) matches the California average (1970).

How Humboldt County compares with California's closest counties by inventory size

The 5 California counties nearest Humboldt County in number of bridges, with their condition splits. Its 6.8% Poor share is the 3rd-lowest of these 6. Its average build year of 1968 against a peer-group mean of 1969 is in line with the group.

Showing the 5 closest of 57 California counties eligible for comparison.

Bridge inventory size and condition shares for Humboldt County and the 5 California counties closest to it in inventory size
County	Bridges	Good	Fair	Poor	Avg. built
Santa Barbara County	418	51.4%	42.8%	5.7%	1975
San Luis Obispo County	401	47.6%	46.6%	5.7%	1970
Humboldt County (this page)	396	38.9%	54.3%	6.8%	1968
Stanislaus County	386	30.8%	55.7%	13.5%	1956
Monterey County	377	56.8%	35.5%	7.7%	1970
Solano County	373	44.8%	47.5%	7.8%	1975

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

Similar inventory size

Nearest county inventories outside CA (396 bridges here).

Nodaway County, MO · 396 bridges
Somerset County, NJ · 397 bridges
Essex County, MA · 395 bridges
Creek County, OK · 395 bridges

Similar average build year

Nearest mean year-built outside CA (1968 here).

Montgomery County, PA · avg 1968 · 828 bridges
Providence County, RI · avg 1968 · 476 bridges
Delaware County, PA · avg 1968 · 387 bridges
Genesee County, MI · avg 1968 · 371 bridges

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

All 396 Good 154 Fair 215 Poor 27

Fair-condition bridges (215)

Sort:

Humboldt County Bridge Snapshot

Condition distribution

Humboldt County's Poor-condition bridges carry 42,605 vehicle crossings a day

69.2% of Humboldt County's bridges have passed the 50-year mark

One structure carries 41.1% of the county's Poor-condition bridge traffic

How Humboldt County compares with California'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 (215)

US HIGHWAY 101 SB

STATE ROUTE 96

CANNIBAL ROAD

PORT KENYON ROAD

DAVISON ROAD

STATE ROUTE 96

TWELFTH ST

BRICELAND-THORNE

STATE ROUTE 96

STATE ROUTE 299

SR 255

U.S. HIGHWAY 101

U.S. HIGHWAY 101

BRICELAND THORN RD

U.S. HIGHWAY 101

U.S. HIGHWAY 101

MAPLE HILLS RD

U.S. HIGHWAY 101

SMITH POINT

BAIR ROAD

REDWOOD DR

PAINTER ST

STEELHEAD RD

WILLIAMS CREEK RD

BRICELAND-THORNE

U.S. HIGHWAY 101

ISHI PISHI RD

STATE ROUTE 211

U.S. HIGHWAY 101

STATE ROUTE 36

STATE ROUTE 299

WILDER RIDGE ROAD

U.S. HIGHWAY 101

S QUARRY ROAD

U.S. HIGHWAY 101

SHIVELEY ROAD

11TH ST

FORT SEWARD ROAD

CENTERVILLE ROAD

STATE ROUTE 211

UPPER BEAR RIV RD

REDWOOD DR

SEVENTH ST

MATTOLE ROAD

MATTOLE ROAD

U. BEAR RIVER ROAD

US HIGHWAY 101 SB

US HIGHWAY 101 NB

SPROWEL CREEK ROAD

MATTOLE ROAD

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