County profile · official public datasets

Sonoma County, CA

609 public highway bridges tracked in the FHWA National Bridge Inventory: 24.1% rated Good, 69% Fair, 6.9% Poor.

609
Public bridges: 24.1%
Good condition: 6.9%
Poor condition

The verdict

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

Sonoma County posts a higher-than-median Poor-condition share among rated counties in the state across large county bridge inventory.

31st
of 58 on Poor share: 6.9%
Poor-condition share: 609
public highway bridges: 1967
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.

Sonoma County Bridge Snapshot

According to the Federal Highway Administration's 2024 National Bridge Inventory, Sonoma County ranks #31 of 58 California counties with at least 5 public highway bridges on Poor-condition share (lower share ranks better; currently 6.9%). Sonoma County, California contains 609 public highway bridges. Roughly 24.1% are rated “Good,” 69% “Fair,” and 6.9% “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

609

Public highway bridges in Sonoma County

Good condition

24.1%

147 of 609 rated 7-9

Fair condition

69%

420 of 609 rated 5-6

Poor condition

6.9%

42 of 609 rated 4 or below

In-state Poor-share rank

#31 of 58

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

Condition distribution

Share of 609 NBI-tracked bridges by lowest applicable component rating.

Good

24.1% (147)

Fair

69% (420)

Poor

6.9% (42)

Sonoma County's Poor-condition bridges carry 340,018 vehicle crossings a day

That is 5.3% of the county's reported daily bridge traffic on 6.9% of its bridges: Poor-condition structures carry less traffic than their share of the inventory. Each Poor bridge averages 8,096 crossings a day against 11,374 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 609 of 609 bridges in this county that report an average daily traffic count. Source: FHWA National Bridge Inventory, 2024 release.

67.2% of Sonoma County's bridges have passed the 50-year mark

409 of the 609 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 24.1% 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 13.4% of the county's Poor-condition bridge traffic

US HIGHWAY 101 over DRY CREEK ROAD, built 1960, carries 45,500 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 42-bridge count understates how much of the daily burden sits on a single crossing.

Share is of the 340,018 daily crossings on Poor-rated bridges that report a traffic count. Source: FHWA National Bridge Inventory, 2024 release.

1900s

6
1910s

14
1920s

46
1930s

29
1940s

12
1950s

69
1960s

160
1970s

113
1980s

42
1990s

49
2000s

31
2010s

30
2020s

8

What this shows Construction peaked in the 1960s, when 160 of the county's bridges still in the inventory were built, which is 26.3% of those with a recorded year. That cohort is now 55 to 64 years old in the 2024 inventory. Its average build year (1967) matches the California average (1970).

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

The 5 California counties nearest Sonoma County in number of bridges, with their condition splits. Its 6.9% Poor share is the 3rd-lowest of these 6. Its average build year of 1967 against a peer-group mean of 1970 is in line with the group.

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

Bridge inventory size and condition shares for Sonoma County and the 5 California counties closest to it in inventory size
County	Bridges	Good	Fair	Poor	Avg. built
Kern County	668	50.1%	43.3%	6.6%	1972
Alameda County	658	35.3%	55.2%	9.6%	1973
San Joaquin County	644	33.7%	57.1%	9.2%	1968
Contra Costa County	618	42.6%	46.9%	10.5%	1977
Sonoma County (this page)	609	24.1%	69%	6.9%	1967
Tulare County	589	42.4%	54.2%	3.4%	1959

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

Similar inventory size

Nearest county inventories outside CA (609 bridges here).

Palm Beach County, FL · 610 bridges
Mobile County, AL · 612 bridges
Allen County, IN · 613 bridges
Weld County, CO · 614 bridges

Similar average build year

Nearest mean year-built outside CA (1967 here).

Allegheny County, PA · avg 1967 · 1,294 bridges
Suffolk County, MA · avg 1967 · 489 bridges
Multnomah County, OR · avg 1967 · 473 bridges
Le Flore County, OK · avg 1967 · 469 bridges

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

All 609 Good 147 Fair 420 Poor 42

Fair-condition bridges (420)

Sort:

Sonoma County Bridge Snapshot

Condition distribution

Sonoma County's Poor-condition bridges carry 340,018 vehicle crossings a day

67.2% of Sonoma County's bridges have passed the 50-year mark

One structure carries 13.4% of the county's Poor-condition bridge traffic

How Sonoma 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 (420)

US HIGHWAY 101 SB

US HIGHWAY 101 NB

MOSCOW RD

MARTINELLI RD

STARRETT HILL DR

SUMMERHOME PARK RD

MARK WEST STA RD

MOSCOW ROAD

US HIGHWAY 101 SB

US HIGHWAY 101 NB

RIVER ROAD

US HIGHWAY 101 SB

US HIGHWAY 101 NB

KING RIDGE RD

STWRT PT-SKGG SPRG

NORTH REDWOOD HWY

STATE ROUTE 128

STATE ROUTE 128

STATE ROUTE 128

STATE ROUTE 116

U.S. HIGHWAY 101

STATE ROUTE 116

STATE ROUTE 128

US HIGHWAY 101

BAKER AVENUE

US HIGHWAY 101

US HIGHWAY 101

STATE ROUTE 1

STATE ROUTE 1

SR 1

US HIGHWAY 101

RAMP/CONNECTOR 101

STATE ROUTE 1

ROHNERT PARK EXPWY

US HIGHWAY 101 NB

E WASHINGTON ST

S CLOVERDALE BLVD

BICENTENNIAL WAY

U.S. HIGHWAY 101

U.S. HIGHWAY 101

SR 12 WB

SR 12 WB

STATE ROUTE 12 EB

STONY POINT RD

HOEN AV-W12 ON RMP

US HIGHWAY 101 SB

US HIGHWAY 101 NB

NB101-ROBERTS LAKE

U.S. HIGHWAY 101

S101-E&W12 CONNCTR

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