County profile · official public datasets

King County, WA

1,238 public highway bridges tracked in the FHWA National Bridge Inventory: 46.5% rated Good, 49.2% Fair, 4.3% Poor.

1,238
Public bridges: 46.5%
Good condition: 4.3%
Poor condition

The verdict

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

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

Top 38%
lowest Poor share in state: 4.3%
Poor-condition share: 1,238
public highway bridges: 1977
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.

King County Bridge Snapshot

According to the Federal Highway Administration's 2024 National Bridge Inventory, King County ranks #15 of 39 Washington counties with at least 5 public highway bridges on Poor-condition share (lower share ranks better; currently 4.3%). King County, Washington contains 1,238 public highway bridges. Roughly 46.5% are rated “Good,” 49.2% “Fair,” and 4.3% “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

1,238

Public highway bridges in King County

Good condition

46.5%

576 of 1,238 rated 7-9

Fair condition

49.2%

609 of 1,238 rated 5-6

Poor condition

4.3%

53 of 1,238 rated 4 or below

In-state Poor-share rank

#15 of 39

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

Condition distribution

Share of 1,238 NBI-tracked bridges by lowest applicable component rating.

Good

46.5% (576)

Fair

49.2% (609)

Poor

4.3% (53)

King County's Poor-condition bridges carry 905,838 vehicle crossings a day

That is 3.2% of the county's reported daily bridge traffic on 4.2% of its bridges: Poor-condition structures carry less traffic than their share of the inventory. Each Poor bridge averages 17,420 crossings a day against 19,020 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 1,235 of 1,238 bridges in this county that report an average daily traffic count. Source: FHWA National Bridge Inventory, 2024 release.

53.6% of King County's bridges have passed the 50-year mark

664 of the 1,238 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 46.5% 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 10.5% of the county's Poor-condition bridge traffic

I-5 over LUCILE ST, built 1966, carries 95,134 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 53-bridge count understates how much of the daily burden sits on a single crossing.

Share is of the 905,838 daily crossings on Poor-rated bridges that report a traffic count. Source: FHWA National Bridge Inventory, 2024 release.

1900s

3
1910s

17
1920s

24
1930s

43
1940s

62
1950s

78
1960s

317
1970s

183
1980s

95
1990s

142
2000s

139
2010s

110
2020s

25

What this shows Construction peaked in the 1960s, when 317 of the county's bridges still in the inventory were built, which is 25.6% of those with a recorded year. That cohort is now 55 to 64 years old in the 2024 inventory. Its average build year (1977) matches the Washington average (1975).

How King County compares with Washington's closest counties by inventory size

The 5 Washington counties nearest King County in number of bridges, with their condition splits. Its 4.3% Poor share is the 4th-lowest of these 6. Its average build year of 1977 against a peer-group mean of 1975 is in line with the group.

Showing the 5 closest of 38 Washington counties eligible for comparison.

Bridge inventory size and condition shares for King County and the 5 Washington counties closest to it in inventory size
County	Bridges	Good	Fair	Poor	Avg. built
King County (this page)	1,238	46.5%	49.2%	4.3%	1977
Yakima County	558	58.2%	36.7%	5%	1973
Snohomish County	500	49%	47%	4%	1980
Pierce County	472	55.3%	40.5%	4.2%	1974
Lewis County	419	39.4%	56.8%	3.8%	1969
Grays Harbor County	363	48.8%	41.9%	9.4%	1978

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

Similar inventory size

Nearest county inventories outside WA (1,238 bridges here).

Oklahoma County, OK · 1,216 bridges
Allegheny County, PA · 1,294 bridges
Williamson County, TX · 1,170 bridges
Orange County, CA · 1,164 bridges

Similar average build year

Nearest mean year-built outside WA (1977 here).

San Diego County, CA · avg 1977 · 1,632 bridges
Riverside County, CA · avg 1977 · 1,117 bridges
Shelby County, TN · avg 1977 · 1,077 bridges
Contra Costa County, CA · avg 1977 · 618 bridges

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

All 1,238 Good 576 Fair 609 Poor 53

Good-condition bridges (576)

Sort:

King County Bridge Snapshot

Condition distribution

King County's Poor-condition bridges carry 905,838 vehicle crossings a day

53.6% of King County's bridges have passed the 50-year mark

One structure carries 10.5% of the county's Poor-condition bridge traffic

How King County compares with Washington'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 (576)

I-90

I-90

US 2

US 2

SR 18 WESTBOUND

E-N RAMP

SR 18

SR 518 EB OFF RAMP

SR 522

ROAD

S 277TH ST

S 156TH WAY

310TH AVE SE

308TH AVE SE

195TH AVE. NE

135TH AVE NE

NE 31ST STREET

I-405 S-W RAMP

SR 522

SR 18

SE 248TH ST

73RD AVE NE

LAKEMONT BLVD

TIBBETTS CK LN NW

N 40TH PLACE

SE 424TH ST

WESTBOUND I-90

SR 167 SB OFF-RAMP

E-N RAMP SR 520

SR 516

I-405 RAMP

SR 18

SR 18

WB I-90

EB I-90

NORTH MERCER WAY

405 N-E RAMP

E LAKE SAMMAMISH

I-405

KELLY RD NE

Riverview Blvd. S

108TH AVE NE

SE 416th ST

72ND AVENUE SOUTH

NB RAMP

I-5 NB HOV

I-405

I-405

SB I-405 RAMP

ROAD

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