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By the Numbers

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Interstate 90 Floating Bridge on
Lake Washington

There are roughly 7,000 bridges on the state, city and county road systems and most are inspected every two years.

When a bridge is built, it is given a design life of 75 years. The average age of state-owned vehicular bridges is now 41 years. WSDOT built a significant number of bridges during the Interstate Program in the 1950s and 1960s. There are now 232 WSDOT bridges that are 75 years old or older.

Most of these bridges are in good to fair condition which is a testimony to sound engineering practices and durable materials; however, age alone is not an indicator of overall bridge condition.


Vehicular Bridges (over 20 ft. long) 3,039
Structures less than 20 ft. long 351
Border Bridges (maintained by border state)* 6
Floating Bridges 4
Culverts greater than 20 feet in width 111
Pedestrian Structures 72
Tunnels and Lids 41
Ferry Terminal Structures 69
Railroad Bridges 5

Every July, we summarize the numbers of state-owned bridges and provide an annual assessment of their condition to the Governor. We also provide a summary in the department's Gray Notebook.

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Barrier separated bicycle and pedestrian
trail on the I-90 Floating Bridge

WSDOT has built 133 vehicular bridges greater than 20 feet in length from 2005 to 2010, that’s an average of nearly 26 bridges per year.

Since June 2007, the number of vehicular bridges has increased from 2,990 to 3,039. This increase is due to new bridges being built and older bridges being replaced within the highway system.

Concrete structures
represent approximately 78% of all WSDOT bridges, as compared to steel (21%) and wood (1%). Over the past ten years, seven out of ten bridges built have been prestressed or post-tensioned concrete structures.

WSDOT owns 275 existing painted steel bridges that require routine painting. There are also eight steel painted bridges that cross a river into a border state for which WSDOT shares the cost of repainting with the border state. Steel bridges typically need to be repainted every 15 to 20 years.

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SR 433 Columbia River Lewis and
Clark Bridge

There are 48 steel deck truss bridges in Washington, 26 state-owned and 22 owned by cities and counties.

There are 15 movable bridges on state highways owned and operated by WSDOT. The department also shares funding responsibility for the maintenance and operations of three additional movable span bridges with Oregon and Idaho. Most of these structures are over 50 years old and have obsolete mechanical and electrical systems. Over the past 10 years, we have been upgrading these bridges to ensure that the lift spans do not fail and impede either roadway or waterway traffic. Sixteen movable bridges have been overhauled with one remaining.

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Galer Street pedestrian overpass over
SR 99 in Seattle

I-82 Selah Creek Fred G. Redmon Bridge