County profile · official public datasets

Sierra County, CA

65 public highway bridges tracked in the FHWA National Bridge Inventory: 40% rated Good, 52.3% Fair, 7.7% Poor.

65
Public bridges: 40%
Good condition: 7.7%
Poor condition

The verdict

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

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

36th
of 58 on Poor share: 7.7%
Poor-condition share: 65
public highway bridges: 1972
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.

Sierra County Bridge Snapshot

According to the Federal Highway Administration's 2024 National Bridge Inventory, Sierra County ranks #36 of 58 California counties with at least 5 public highway bridges on Poor-condition share (lower share ranks better; currently 7.7%). Sierra County, California contains 65 public highway bridges. Roughly 40% are rated “Good,” 52.3% “Fair,” and 7.7% “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

Public highway bridges in Sierra County

Good condition

40%

26 of 65 rated 7-9

Fair condition

52.3%

34 of 65 rated 5-6

Poor condition

7.7%

5 of 65 rated 4 or below

In-state Poor-share rank

#36 of 58

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

Condition distribution

Share of 65 NBI-tracked bridges by lowest applicable component rating.

Good

40% (26)

Fair

52.3% (34)

Poor

7.7% (5)

Sierra County's Poor-condition bridges carry 3,340 vehicle crossings a day

That is 9.6% of the county's reported daily bridge traffic on 7.7% of its bridges: Poor-condition structures carry more traffic than their share of the inventory. Each Poor bridge averages 668 crossings a day against 926 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 65 of 65 bridges in this county that report an average daily traffic count. Source: FHWA National Bridge Inventory, 2024 release.

58.5% of Sierra County's bridges have passed the 50-year mark

38 of the 65 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 40% 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 29.9% of the county's Poor-condition bridge traffic

RAILROAD AVENUE over EAST BRANCH SMITHNECK CR, built 1987, carries 1,000 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 5-bridge count understates how much of the daily burden sits on a single crossing.

Share is of the 3,340 daily crossings on Poor-rated bridges that report a traffic count. Source: FHWA National Bridge Inventory, 2024 release.

1930s

6
1940s

2
1950s

8
1960s

19
1970s

10
1980s

9
1990s

1
2000s

4
2010s

2
2020s

4

What this shows Construction peaked in the 1960s, when 19 of the county's bridges still in the inventory were built, which is 29.2% of those with a recorded year. That cohort is now 55 to 64 years old in the 2024 inventory. Its average build year (1972) matches the California average (1970).

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

The 5 California counties nearest Sierra County in number of bridges, with their condition splits. Its 7.7% Poor share is the 3rd-lowest of these 6. Its average build year of 1972 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 Sierra County and the 5 California counties closest to it in inventory size
County	Bridges	Good	Fair	Poor	Avg. built
Modoc County	87	49.4%	49.4%	1.1%	1969
San Benito County	76	46.1%	43.4%	10.5%	1971
Inyo County	66	63.6%	31.8%	4.5%	1972
Sierra County (this page)	65	40%	52.3%	7.7%	1972
Amador County	61	37.7%	37.7%	24.6%	1966
Mono County	49	63.3%	24.5%	12.2%	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 Sierra 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 Sierra County, both outside California so the neighborhoods are not the same-state size table above.

Similar inventory size

Nearest county inventories outside CA (65 bridges here).

Marion County, AR · 65 bridges
Newton County, AR · 65 bridges
Searcy County, AR · 65 bridges
Pierce County, GA · 65 bridges

Similar average build year

Nearest mean year-built outside CA (1972 here).

Madison County, AL · avg 1972 · 710 bridges
York County, PA · avg 1972 · 569 bridges
Middlesex County, NJ · avg 1972 · 563 bridges
Saunders County, NE · avg 1972 · 506 bridges

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

All 65 Good 26 Fair 34 Poor 5

All bridges (65)

Sort:

Sierra County Bridge Snapshot

Condition distribution

Sierra County's Poor-condition bridges carry 3,340 vehicle crossings a day

58.5% of Sierra County's bridges have passed the 50-year mark

One structure carries 29.9% of the county's Poor-condition bridge traffic

How Sierra 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

All bridges (65)

ROAD 20N06

FDR 524-1-2

FDR 39

C 843

JIM CROW ROAD

MOUNTIAN HOUSE RD

SALMON LAKE ROAD

WILD PLUM ROAD

NEVADA STREET

PEARL STREET

PLUMBAGO ROAD

MOUNTAIN HOUSE RD

POST OFFICE SPUR

MOUNTAIN HOUSE RD

WESTSIDE RD

PORT WINE RIDGE RD

LEMON CANYON ROAD

PORT WINE RIDGE RD

PORT WINE RIDGE RD

PORT WINE RIDGE RD

FDR 524-01

STATE ROUTE 49

STATE ROUTE 49

STATE ROUTE 49

STATE ROUTE 89

GOODYEARS CREEK RD

MAIN ST CR S500

GOLD LAKE ROAD

CROW CITY ROAD

MOUNTAIN HOUSE RD

BRANDY CITY ROAD

STATE ROUTE 49

BRANDY CITY ROAD

LAVEZZOLA ROAD

STATE ROUTE 49

NO DATA ENTERED

STATE ROUTE 89

STATE ROUTE 89

STATE ROUTE 49

STATE ROUTE 49

SR 49

STATE ROUTE 49

STATE ROUTE 49

STATE ROUTE 49

STATE ROUTE 49

HENNESS PASS ROAD

SIERRA BUTTE ROAD

OLD FIBREBOARD RD

STATE ROUTE 49

STATE ROUTE 49

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