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Annual county bridge report outlines needs

King County’s annual report on the condition of its 185 bridges shows the county continues to make major strides toward improving the overall safety and condition of its bridges. Construction of 17 new bridges in the last decade and near-completion of a 14-year earthquake retrofit program have helped increase the reliability of the county’s bridges. However, several aging spans continue to be of concern – including the South Park Bridge over the Duwamish River.

photo: South Park Bridge
South Park Bridge.

The 2006 King County Annual Bridge Report was recently finalized and published. The purpose of the yearly report is to give the county executive, county council, and residents a snapshot of the health of the county’s bridge system. Overall, the news is very good.

The report details an ambitious era of bridge construction. Over the past decade, the county made major improvements to a number of spans including the Elliott, Novelty, Preston, York, Cedar Mountain, Northeast 124th Street, and Duvall bridges. Currently, the county is replacing Mt. Si, Tolt and Wagners bridges in East King County. Those projects will be finished in 2008.

As a result, the county has seen the average sufficiency rating of its bridges climb from 64.1 to 68.3 on a scale of 100 over the past five years. The federal government uses the 0-100 sufficiency scale to rate bridges on structural adequacy, serviceability, and essentiality for public use.

The 76-year-old South Park Bridge, one of two county steel deck truss bridges, remains a concern. A recent inspection found that while it is safe, the South Park Bridge is reaching the end of its useful life and the sufficiency rating was only 4 on the 0-100 scale. Engineers say close monitoring should continue, but that the bridge needs to be replaced or torn down by the end of this decade. Replacement is estimated at $150 million, $110 of which is included in a fall ballot measure.

photo: bridge inspection.
County engineers inspecting a bridge.

Other aging bridges in need of replacement in the coming years include: Alvord T. Bridge spanning the Green River Near Kent; Berrydale Overcrossing on Kent-Black Diamond Road; and Patterson Creek Bridge on Duthie Hill Road near Sammamish.

Sims’ 2007 budget, which emphasized the importance of investing in infrastructure, included acceleration of an aggressive Short Span Bridge Program aimed at replacing 57 bridges that are less than 20-feet long. County engineers are aiming to replace 24 of the county’s short span bridges over the next six years at a cost of $17 million.

The county is also nearing completion of a major 14-year seismic retrofit program. By the end of 2008, the King County Road Services Division expects to strengthen the remaining five bridges needing retrofitting. Similar projects have already been completed on 110 county spans. That work will help prevent bridge collapses during an earthquake.

The 2006 Annual Bridge Report is available online.

 
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Updated:  August 27, 2007

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