County profile · official public datasets

San Mateo County, CA

361 public highway bridges tracked in the FHWA National Bridge Inventory: 26% rated Good, 64% Fair, 10% Poor.

361
Public bridges: 26%
Good condition: 10%
Poor condition

The verdict

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

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

45th
of 58 on Poor share: 10%
Poor-condition share: 361
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.

San Mateo County Bridge Snapshot

According to the Federal Highway Administration's 2024 National Bridge Inventory, San Mateo County ranks #45 of 58 California counties with at least 5 public highway bridges on Poor-condition share (lower share ranks better; currently 10%). San Mateo County, California contains 361 public highway bridges. Roughly 26% are rated “Good,” 64% “Fair,” and 10% “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

361

Public highway bridges in San Mateo County

Good condition

26%

94 of 361 rated 7-9

Fair condition

64%

231 of 361 rated 5-6

Poor condition

10%

36 of 361 rated 4 or below

In-state Poor-share rank

#45 of 58

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

Condition distribution

Share of 361 NBI-tracked bridges by lowest applicable component rating.

Good

26% (94)

Fair

64% (231)

Poor

10% (36)

San Mateo County's Poor-condition bridges carry 1,452,025 vehicle crossings a day

That is 11.8% of the county's reported daily bridge traffic on 10% of its bridges: Poor-condition structures carry more traffic than their share of the inventory. Each Poor bridge averages 40,334 crossings a day against 38,111 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 361 of 361 bridges in this county that report an average daily traffic count. Source: FHWA National Bridge Inventory, 2024 release.

70.6% of San Mateo County's bridges have passed the 50-year mark

255 of the 361 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 26% 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

U.S. HIGHWAY 101 over CORDILLERAS CREEK, built 1930, carries 195,000 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 36-bridge count understates how much of the daily burden sits on a single crossing.

Share is of the 1,452,025 daily crossings on Poor-rated bridges that report a traffic count. Source: FHWA National Bridge Inventory, 2024 release.

1900s

11
1910s

7
1920s

11
1930s

13
1940s

15
1950s

38
1960s

108
1970s

76
1980s

32
1990s

23
2000s

20
2010s

7

What this shows Construction peaked in the 1960s, when 108 of the county's bridges still in the inventory were built, which is 29.9% 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 San Mateo County compares with California's closest counties by inventory size

The 5 California counties nearest San Mateo County in number of bridges, with their condition splits. Its 10% Poor share is the 5th-lowest of these 6. Its average build year of 1967 against a peer-group mean of 1969 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 Mateo County and the 5 California counties closest to it in inventory size
County	Bridges	Good	Fair	Poor	Avg. built
Stanislaus County	386	30.8%	55.7%	13.5%	1956
Monterey County	377	56.8%	35.5%	7.7%	1970
Solano County	373	44.8%	47.5%	7.8%	1975
San Mateo County (this page)	361	26%	64%	10%	1967
Mendocino County	357	34.7%	57.7%	7.6%	1969
Placer County	337	44.2%	51.6%	4.2%	1976

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

Similar inventory size

Nearest county inventories outside CA (361 bridges here).

Washita County, OK · 361 bridges
Richland County, SC · 361 bridges
Gibson County, IN · 362 bridges
Fayette County, IA · 362 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 361 Good 94 Fair 231 Poor 36

Good-condition bridges (94)

Sort:

San Mateo County Bridge Snapshot

Condition distribution

San Mateo County's Poor-condition bridges carry 1,452,025 vehicle crossings a day

70.6% of San Mateo County's bridges have passed the 50-year mark

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

How San Mateo 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 (94)

NORTH B STREET

CRYSTAL SPRINGS RD

DELAWARE ST

N CLAREMONT

OLD COUNTY RD

FREMONT ST

SIERRA DRIVE

KINGS MOUNTAIN RD

CANYON ROAD

NIMITZ DRIVE

STATE ROUTE 92

STATE ROUTE 84

WHIPPLE AVENUE

U.S. HIGHWAY 101

U.S. HIGHWAY 101

INDUSTRIAL WAY

MARINE PKWY

DELAWARE ST

MARSH RD

ROAD-1 SOUTH

STATE PARK RD

UNIVERSITY AVE

STATE ROUTE 84

I-280 SB ONRAMP

STATE ROUTE 92

STAGE RD

WILLOWBROOK DR

STATE ROUTE 1

STATE ROUTE 84

3RD AVE-N101 ON RP

N101-3RD AV OFFRMP

FASHION ISLAND BL

U.S. HIGHWAY 101

SR 84 (MARSH RD)

U.S. HIGHWAY 101

MAPLE STREET

S101-3RD AVE OFFRP

STATE ROUTE 1 SB

STATE ROUTE 1 NB

STATE ROUTE 1

RALSTON POLHEMUS R

SB STATE RTE 280

S280-SAN BRUNO OFF

INTERSTATE 280 SB

U.S. HIGHWAY 101

MARINERS ISLAND BL

STATE ROUTE 84

U.S. HIGHWAY 101

OYSTER POINT BLVD

S101-OYSTER POINT

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