County profile · official public datasets

San Luis Obispo County, CA

401 public highway bridges tracked in the FHWA National Bridge Inventory: 47.6% rated Good, 46.6% Fair, 5.7% Poor.

401
Public bridges: 47.6%
Good condition: 5.7%
Poor condition

The verdict

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

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

Top 33%
lowest Poor share in state: 5.7%
Poor-condition share: 401
public highway bridges: 1970
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.

San Luis Obispo County Bridge Snapshot

According to the Federal Highway Administration's 2024 National Bridge Inventory, San Luis Obispo County ranks #19 of 58 California counties with at least 5 public highway bridges on Poor-condition share (lower share ranks better; currently 5.7%). San Luis Obispo County, California contains 401 public highway bridges. Roughly 47.6% are rated “Good,” 46.6% “Fair,” and 5.7% “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

401

Public highway bridges in San Luis Obispo County

Good condition

47.6%

191 of 401 rated 7-9

Fair condition

46.6%

187 of 401 rated 5-6

Poor condition

5.7%

23 of 401 rated 4 or below

In-state Poor-share rank

#19 of 58

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

Condition distribution

Share of 401 NBI-tracked bridges by lowest applicable component rating.

Good

47.6% (191)

Fair

46.6% (187)

Poor

5.7% (23)

San Luis Obispo County's Poor-condition bridges carry 228,907 vehicle crossings a day

That is 6.4% of the county's reported daily bridge traffic on 5.7% of its bridges: Poor-condition structures carry more traffic than their share of the inventory. Each Poor bridge averages 9,952 crossings a day against 12,256 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 401 of 401 bridges in this county that report an average daily traffic count. Source: FHWA National Bridge Inventory, 2024 release.

64.1% of San Luis Obispo County's bridges have passed the 50-year mark

257 of the 401 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 47.6% 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 13.1% of the county's Poor-condition bridge traffic

NIBLICK ROAD over US HIGHWAY 101, built 1987, carries 30,055 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 23-bridge count understates how much of the daily burden sits on a single crossing.

Share is of the 228,907 daily crossings on Poor-rated bridges that report a traffic count. Source: FHWA National Bridge Inventory, 2024 release.

1900s

2
1910s

9
1920s

16
1930s

12
1940s

29
1950s

89
1960s

85
1970s

31
1980s

19
1990s

46
2000s

25
2010s

26
2020s

12

What this shows Construction peaked in the 1950s, when 89 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 65 to 74 years old in the 2024 inventory. Its average build year (1970) matches the California average (1970).

How San Luis Obispo County compares with California's closest counties by inventory size

The 5 California counties nearest San Luis Obispo County in number of bridges, with their condition splits. Its 5.7% Poor share is the 2nd-lowest of these 6. Its average build year of 1970 against a peer-group mean of 1968 is in line with the group.

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

Bridge inventory size and condition shares for San Luis Obispo County and the 5 California counties closest to it in inventory size
County	Bridges	Good	Fair	Poor	Avg. built
Siskiyou County	421	39%	55.6%	5.5%	1971
Santa Barbara County	418	51.4%	42.8%	5.7%	1975
San Luis Obispo County (this page)	401	47.6%	46.6%	5.7%	1970
Humboldt County	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

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

Similar inventory size

Nearest county inventories outside CA (401 bridges here).

Vernon County, MO · 401 bridges
Randolph County, NC · 401 bridges
Jackson County, OR · 401 bridges
Marshall County, KS · 402 bridges

Similar average build year

Nearest mean year-built outside CA (1970 here).

Hamilton County, OH · avg 1970 · 783 bridges
Yavapai County, AZ · avg 1970 · 543 bridges
Garfield County, OK · avg 1970 · 504 bridges
Somerset County, NJ · avg 1970 · 397 bridges

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

All 401 Good 191 Fair 187 Poor 23

Good-condition bridges (191)

Sort:

San Luis Obispo County Bridge Snapshot

Condition distribution

San Luis Obispo County's Poor-condition bridges carry 228,907 vehicle crossings a day

64.1% of San Luis Obispo County's bridges have passed the 50-year mark

One structure carries 13.1% of the county's Poor-condition bridge traffic

How San Luis Obispo 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 (191)

QUAILWOOD LANE

MAIN ST

MAIN ST

ADOBE ROAD

US HIGHWAY 101 SB

SAN LUIS BAY DR

US HIGHWAY 101 NB

US HIGHWAY 101 NB

STATE ROUTE 46

STATE ROUTE 46

MORRO BAY BLVD

HINDS AVE

SANTA ROSA CR RD

US HIGHWAY 101 NB

US HIGHWAY 101 SB

US HIGHWAY 101 SB

SANTA ROSA CR RD

US HIGHWAY 101 NB

LAS PILITAS RD

U.S. HIGHWAY 101

I STREET

ESTRELLA RD

PREFUMO CANYON RD

EL CAMINO REAL

US HIGHWAY 101 NB

ATASCADERO ROAD

US HIGHWAY 101 NB

STATE ROUTE 1

US HIGHWAY 101 NB

STATE ROUTE 1

US HIGHWAY 101 SB

MAIN STREET

WINDSOR BLVD

FERROCARRIL RD

EL CAMINO REAL

US HIGHWAY 101 SB

US HIGHWAY 101 NB

SAN LUIS BAY DR

US HIGHWAY 101 SB

US HIGHWAY 101 NB

LAKEVIEW DR

US HIGHWAY 101 NB

STATE ROUTE 227

STATE ROUTE 227

US HIGHWAY 101 SB

US HIGHWAY 101 SB

LOS OSOS VALLEY RD

US HIGHWAY 101 NB

STATE ROUTE 1

STATE ROUTE 1

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