County profile · official public datasets

Napa County, CA

158 public highway bridges tracked in the FHWA National Bridge Inventory: 45.6% rated Good, 50% Fair, 4.4% Poor.

158
Public bridges: 45.6%
Good condition: 4.4%
Poor condition

The verdict

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

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

Top 24%
lowest Poor share in state: 4.4%
Poor-condition share: 158
public highway bridges: 1961
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.

Napa County Bridge Snapshot

According to the Federal Highway Administration's 2024 National Bridge Inventory, Napa County ranks #14 of 58 California counties with at least 5 public highway bridges on Poor-condition share (lower share ranks better; currently 4.4%). Napa County, California contains 158 public highway bridges. Roughly 45.6% are rated “Good,” 50% “Fair,” and 4.4% “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

158

Public highway bridges in Napa County

Good condition

45.6%

72 of 158 rated 7-9

Fair condition

50%

79 of 158 rated 5-6

Poor condition

4.4%

7 of 158 rated 4 or below

In-state Poor-share rank

#14 of 58

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

Condition distribution

Share of 158 NBI-tracked bridges by lowest applicable component rating.

Good

45.6% (72)

Fair

50% (79)

Poor

4.4% (7)

Napa County's Poor-condition bridges carry 71,412 vehicle crossings a day

That is 5.5% of the county's reported daily bridge traffic on 4.4% of its bridges: Poor-condition structures carry more traffic than their share of the inventory. Each Poor bridge averages 10,202 crossings a day against 8,868 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 158 of 158 bridges in this county that report an average daily traffic count. Source: FHWA National Bridge Inventory, 2024 release.

63.9% of Napa County's bridges have passed the 50-year mark

101 of the 158 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 45.6% 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 67.2% of the county's Poor-condition bridge traffic

STATE ROUTE 29 over NVRR NAPA RIVER STANLY, built 1977, carries 48,000 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 7-bridge count understates how much of the daily burden sits on a single crossing.

Share is of the 71,412 daily crossings on Poor-rated bridges that report a traffic count. Source: FHWA National Bridge Inventory, 2024 release.

pre-1900

3
1900s

11
1910s

7
1920s

12
1930s

17
1940s

7
1950s

13
1960s

18
1970s

18
1980s

18
1990s

7
2000s

11
2010s

11
2020s

5

What this shows Construction peaked in the 1960s, when 18 of the county's bridges still in the inventory were built, which is 11.4% of those with a recorded year. That cohort is now 55 to 64 years old in the 2024 inventory. Its average build year is 1961, 9 years older than the California average of 1970.

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

The 5 California counties nearest Napa County in number of bridges, with their condition splits. Its 4.4% Poor share is the 2nd-lowest of these 6. Its average build year of 1961 against a peer-group mean of 1969 is 8 years older.

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

Bridge inventory size and condition shares for Napa County and the 5 California counties closest to it in inventory size
County	Bridges	Good	Fair	Poor	Avg. built
Kings County	168	40.5%	53.6%	6%	1968
Plumas County	165	26.7%	69.1%	4.2%	1965
Napa County (this page)	158	45.6%	50%	4.4%	1961
San Francisco County	143	34.3%	51%	14.7%	1969
Nevada County	135	45.2%	40.7%	14.1%	1972
Lake County	129	30.2%	62%	7.8%	1970

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

Similar inventory size

Nearest county inventories outside CA (158 bridges here).

Wells County, IN · 158 bridges
Jackson County, MI · 158 bridges
Yalobusha County, MS · 158 bridges
Fergus County, MT · 158 bridges

Similar average build year

Nearest mean year-built outside CA (1961 here).

Westchester County, NY · avg 1961 · 774 bridges
Berkshire County, MA · avg 1961 · 450 bridges
Schuylkill County, PA · avg 1961 · 368 bridges
Columbiana County, OH · avg 1961 · 321 bridges

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

All 158 Good 72 Fair 79 Poor 7

Fair-condition bridges (79)

Sort:

Napa County Bridge Snapshot

Condition distribution

Napa County's Poor-condition bridges carry 71,412 vehicle crossings a day

63.9% of Napa County's bridges have passed the 50-year mark

One structure carries 67.2% of the county's Poor-condition bridge traffic

How Napa 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 (79)

SR 121 EB IMOLA AV

COOK ROAD

SILVERADO TRAIL

SILVERADO TRAIL

SOSCOL AVE

REDWOOD ROAD

LAS AMIGAS RD

POPE CANYON RD

YOUNTVILLE CROSS R

POPE CANYON ROAD

FOURTH AVE

SOSCOL AVE

FIRST STREET

DEVLIN ROAD

POPE CANYON ROAD (

ATLAS PEAK ROAD

BUTTS CANYON RD

OAKVILLE CROSS RD

BIG RANCH ROAD

LOMA VISTA DR

HARDMAN AVENUE

LINCOLN AVENUE

STATE ROUTE 29 SB

STATE ROUTE 121

STATE ROUTE 29 NB

KNOXV-BERRYESSA RD

STATE ROUTE 29 NB

TRANCAS ST

REDWOOD ROAD

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