Total bridges
401
Public highway bridges in San Luis Obispo County
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.
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.
When San Luis Obispo County's bridges were built
401 bridges with a recorded construction year, grouped by decade
- 1900s 2
1900–1909
2 bridges
- 1910s 9
1910–1919
9 bridges
- 1920s 16
1920–1929
16 bridges
- 1930s 12
1930–1939
12 bridges
- 1940s 29
1940–1949
29 bridges
- 1950s
1950–1959
89 bridges
- 1960s
1960–1969
85 bridges
- 1970s 31
1970–1979
31 bridges
- 1980s 19
1980–1989
19 bridges
- 1990s
1990–1999
46 bridges
- 2000s 25
2000–2009
25 bridges
- 2010s 26
2010–2019
26 bridges
- 2020s 12
2020–2029
12 bridges
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.
| 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 bridges (401)
Read our methodology - how this data is sourced, computed, and verified.
Related
Data sourced from official public datasets. See our methodology for details. Retrieved and formatted by PlainBridges
Every figure on PlainBridges is rendered directly from federal source data, no number is typed in by an editor. This page draws directly on federal source data, no figure is typed in by an editor. See our editorial standards & corrections policy, the methodology behind these numbers, or report a data error. NBI condition categories reflect the latest reported inventory record, not a live safety, closure, or travel decision.