County profile · official public datasets

Trinity County, CA

194 public highway bridges tracked in the FHWA National Bridge Inventory: 56.2% rated Good, 39.7% Fair, 4.1% Poor.

194
Public bridges: 56.2%
Good condition: 4.1%
Poor condition

The verdict

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

Trinity 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 17%
lowest Poor share in state: 4.1%
Poor-condition share: 194
public highway bridges: 1977
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.

Trinity County Bridge Snapshot

According to the Federal Highway Administration's 2024 National Bridge Inventory, Trinity County ranks #10 of 58 California counties with at least 5 public highway bridges on Poor-condition share (lower share ranks better; currently 4.1%). Trinity County, California contains 194 public highway bridges. Roughly 56.2% are rated “Good,” 39.7% “Fair,” and 4.1% “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

194

Public highway bridges in Trinity County

Good condition

56.2%

109 of 194 rated 7-9

Fair condition

39.7%

77 of 194 rated 5-6

Poor condition

4.1%

8 of 194 rated 4 or below

In-state Poor-share rank

#10 of 58

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

Condition distribution

Share of 194 NBI-tracked bridges by lowest applicable component rating.

Good

56.2% (109)

Fair

39.7% (77)

Poor

4.1% (8)

Trinity County's Poor-condition bridges carry 1,130 vehicle crossings a day

That is 1% of the county's reported daily bridge traffic on 4.1% of its bridges: Poor-condition structures carry less traffic than their share of the inventory. Each Poor bridge averages 141 crossings a day against 529 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 194 of 194 bridges in this county that report an average daily traffic count. Source: FHWA National Bridge Inventory, 2024 release.

53.6% of Trinity County's bridges have passed the 50-year mark

104 of the 194 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 56.2% 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 29.2% of the county's Poor-condition bridge traffic

HYAMPOM ROAD over LITTLE CREEK, built 1955, carries 330 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 8-bridge count understates how much of the daily burden sits on a single crossing.

Share is of the 1,130 daily crossings on Poor-rated bridges that report a traffic count. Source: FHWA National Bridge Inventory, 2024 release.

1900s

1
1920s

1
1930s

4
1940s

9
1950s

25
1960s

43
1970s

40
1980s

18
1990s

8
2000s

25
2010s

18
2020s

2

What this shows Construction peaked in the 1960s, when 43 of the county's bridges still in the inventory were built, which is 22.2% of those with a recorded year. That cohort is now 55 to 64 years old in the 2024 inventory. Its average build year is 1977, 7 years newer than the California average of 1970.

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

The 5 California counties nearest Trinity County in number of bridges, with their condition splits. Its 4.1% Poor share is the 1st-lowest of these 6. Its average build year of 1977 against a peer-group mean of 1966 is 11 years newer.

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

Bridge inventory size and condition shares for Trinity County and the 5 California counties closest to it in inventory size
County	Bridges	Good	Fair	Poor	Avg. built
Colusa County	211	40.8%	52.1%	7.1%	1968
Marin County	207	43.5%	46.9%	9.7%	1958
Trinity County (this page)	194	56.2%	39.7%	4.1%	1977
El Dorado County	192	46.9%	46.9%	6.3%	1975
Santa Cruz County	192	40.1%	42.2%	17.7%	1963
Kings County	168	40.5%	53.6%	6%	1968

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

Similar inventory size

Nearest county inventories outside CA (194 bridges here).

Franklin County, AL · 194 bridges
Poinsett County, AR · 194 bridges
Colquitt County, GA · 194 bridges
Adams County, IN · 194 bridges

Similar average build year

Nearest mean year-built outside CA (1977 here).

King County, WA · avg 1977 · 1,238 bridges
Shelby County, TN · avg 1977 · 1,077 bridges
Chautauqua County, NY · avg 1977 · 559 bridges
St. Clair County, IL · avg 1977 · 486 bridges

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

All 194 Good 109 Fair 77 Poor 8

Good-condition bridges (109)

Sort:

Trinity County Bridge Snapshot

Condition distribution

Trinity County's Poor-condition bridges carry 1,130 vehicle crossings a day

53.6% of Trinity County's bridges have passed the 50-year mark

One structure carries 29.2% of the county's Poor-condition bridge traffic

How Trinity 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

Good-condition bridges (109)

STATE ROUTE 3

STATE ROUTE 3

STATE ROUTE 299

STATE ROUTE 299

STATE ROUTE 36

STATE ROUTE 3

EAGLE CRK LOOP RD

RAMSHORN ROAD

RUTH-ZENIA ROAD

MILL STREET

COFFEE CREEK ROAD

COFFEE CREEK ROAD

OREGON STREET

RUTH-ZENIA ROAD

HOAGLIN ROAD

DEERLICK SPRING RD

MAD RIVER ROAD

MAD RIVER ROAD

EVANS BAR ROAD

DUTCH CREEK ROAD

EAST FORK ROAD

ROUNDY ROAD

BIG CREEK ROAD

UPPER MAD RIVER RD

LANCE GULCH ROAD

UPPER MAD RIVER RD

WEST VAN DUZEN RD

COFFEE CREEK ROAD

RAMSHORN ROAD

JORDAN ROAD

COFFEE CREEK ROAD

E. FORK HAYFORK RD

NO DATA ENTERED

BROWNS RANCH ROAD

STATE ROUTE 3

STATE ROUTE 3

EAST FORK ROAD

COFFEE CREEK ROAD

STATE ROUTE 3

RUTH-ZENIA ROAD

ST. JOHN LOOP ROAD

BARKER CR.

STATE ROUTE 3

STATE ROUTE 36

STATE ROUTE 299

CORRAL BOTTOM ROAD

ZENIA BLUFF RD

STATE ROUTE 299

NO DATA ENTERED

STATE ROUTE 36

Related