King County Bridge Report Card
King County scores 83 out of 100 on BridgeLookup's Bridge Condition Exposure Score, based on FHWA National Bridge Inventory records.
King County, Washington
King County has 1,250 bridges in the National Bridge Inventory, with 50 rated poor and 43 rated scour-critical. Its poor-condition share of 4.0% is at or below the 5.6% statewide average. Poor-condition bridges carry about 920,598 daily vehicle crossings.
Quote-Ready Local Facts
Copyable Facts for Reporters
BridgeLookup.com gives King County a Bridge Condition Exposure Score of 83/100 (B). The county has 1,250 bridges in the National Bridge Inventory, including 50 in poor condition and 43 rated scour-critical. Poor-condition bridges carry about 920,598 daily vehicle crossings. Poor condition does not mean unsafe; bridges judged unsafe are closed or restricted by transportation agencies.
How the Score Breaks Down
| Factor | Weight | County Value | Penalty |
|---|---|---|---|
| Poor-condition bridge share | 40 | 4.0% | 8.0 |
| Poor-condition traffic exposure | 25 | 3.4% of measured traffic | 2.5 |
| Scour-critical bridge share | 20 | 3.4% | 6.9 |
| Average age vs national baseline | 10 | 48 years vs 48 nationally | 0.0 |
| Traffic-data completeness | 5 | 27,432,019 measured daily crossings | 0.0 |
Score = 100 minus weighted penalties. The score is a comparative research signal, not an official safety rating. Read the full methodology.
County Comparisons
| County Poor-Condition Share | 4.0% |
| State Poor-Condition Share | 5.6% |
| National Poor-Condition Share | 6.7% |
| County Scour-Critical Share | 3.4% |
| Average Bridge Age | 48 years |
| Poor-Condition Traffic Exposure | 920,598 vehicles/day |
Bridges to Watch
Top Bridges to Watch in King County
| Bridge | Reason | Condition | Daily Traffic | Year Built |
|---|---|---|---|---|
| SR 202 over Snoqualmie River | Poor condition + traffic exposure | Poor | 9,740 | 1931 |
| US 2 over Anthracite Creek | Poor condition + traffic exposure | Poor | 5,782 | 1940 |
| 428th AVE SE over N Fk Snoqualmie R | Poor condition + traffic exposure | Poor | 1,200 | 1951 |
| SE Mud Mt RD over Boise Creek | Poor condition + traffic exposure | Poor | 947 | 1956 |
| Homestead Vlly RD over S Fk Snoqualmie River | Poor condition + traffic exposure | Poor | 200 | 1974 |
| NE Index Ck RD over Skykomish River-s Fork | Poor condition + traffic exposure | Poor | 80 | 1930 |
| I-5 over Lucile ST | Poor condition + traffic exposure | Poor | 96,847 | 1966 |
| I-90 over Mercer Slough | Poor condition + traffic exposure | Poor | 74,410 | 1940 |
| I-90 over Mercer Sl | Poor condition + traffic exposure | Poor | 74,410 | 1970 |
| I-90 over Lake Washington | Poor condition + traffic exposure | Poor | 68,544 | 1940 |
Important safety note
Poor condition does not mean a bridge is unsafe. It means at least one major component has significant deterioration and the bridge is a priority for maintenance, repair, or replacement. Bridges judged unsafe are closed or restricted by transportation agencies.