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Bridges - By the Numbers

see caption below photo
Interstate 90 Floating Bridge on
Lake Washington

There are roughly 7,300 bridges (61.8M SF) on the state, City and county road systems that are over 20 feet in length and carry vehicular traffic.

A bridge is expected to have a service life of 75 years based on current standards. The average age of state owned vehicular bridges is 45 years.

The Interstate program in the 1950s and 1960s included a significant number of new bridges.  There are 310 WSDOT bridges (1.6M SF) that are 75 years old or older.

Bridge age alone is not an indicator of an overall bridge’s condition.  Bridges are thoroughly inspected based on national FHWA standards to access and rate their condition. Currently, nearly 92% of WSDOT owned bridges are in Good or Fair condition.

WSDOT Bridge Inventory

Vehicular Bridges (over 20 feet in length) 3,093
Structures less than 20 feet in length 402
Culverts (over 20 feet in length) 131
Pedestrian Structures 76
Ferry terminal structures 68
Tunnels and lids 43
Border bridges maintained by border state 6
Border bridges maintained by WSDOT 5
Railroad bridges 5

Every July, we summarize the numbers of state-owned bridges and provide an annual assessment of their condition to the Governor. See the GNB54 - Bridge Assessment for more information. We also provide a summary of past bridge subjects in the department's Gray Notebook.

see caption below photo
Barrier separated bicycle and pedestrian
trail on the I-90 Floating Bridge

WSDOT has built 226 vehicular bridges greater than 20 feet in length from 2005 to 2015, that’s an average of nearly 22 bridges per year.

WSDOT bridges have been constructed using three primary materials: concrete, steel or timber. Concrete structures represent approximately 74% of all WSDOT bridges (by deck area), as compared to steel (25%) and timber (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 20 to 25 years.

see caption below photo
SR 433 Columbia River Lewis and
Clark Bridge

WSDOT has 99 Thru type steel trusses and 48 steel deck truss bridges in it inventory. These bridges receive special inspections due to their fracture critical designation by the FHWA.

There are 13 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 mechanical and electrical systems that require periodic maintenance and upgrades.

There are nearly 100 WSDOT owned bridges with timber spans. The average age of these bridges is 69 years with the oldest being 94 years old. Timber bridges are being continually repaired by state maintenance forces. These bridges will be replaced as conditions warrant and funding allows.

US 101 Bone River

US 101 Bone River - old and new bridge