Bridge & structure preservation
Learn how we preserve, inspect and rate the condition of Washington state bridges.
We inspect the approximately 7,300 bridges on state, city and county road systems. Most are inspected every two years. Bridges are inspected to ensure they are in good working order and to help prioritize maintenance and preservation work.
Our engineers and technicians perform bridge inspections, and have several teams for specialty work including:
- A dive team that performs work under water.
- Aerial inspections using an under-bridge-inspection-truck (UBIT).
- Mechanical and electrical inspectors that inspect moveable parts of a bridge.
We also conduct field reviews and provide training and technical assistance to Washington cities and counties for inspecting bridges on local roads.
Bridge preservation programs
Bridge preservation work includes bridge seismic retrofit, repairs and rehabilitation, steel bridge painting, concrete deck rehabilitation, scour mitigation and bridge replacement. These programs combine cost effective actions and strategies to maximize the useful life of bridges.
Seismic retrofit program
The Seismic retrofit program works to minimize and avoid catastrophic bridge failures by strengthening bridges and structures to better withstand earthquakes.
The most common type of retrofit adds steel jackets around the columns and additional concrete-and-steel reinforcing to the pier caps (also known as a “bolster”).
More than 900 bridges are part of the bridge seismic retrofit program. Retrofit priorities are based on seismic risk of a site, structural detail deficiencies and route importance.
We work with the Washington State Department of Emergency Management, local emergency planners and freight advocates to identify a network of essential state highways in the areas of Puget Sound with the largest predicted ground motion and the highest density of population. Focusing limited resources on these routes further reduces the risk of major damage. This network of state highways is identified as the Seismic Lifeline Routes. The Seismic Lifeline program tracks the status of seismic retrofits made to high and moderate-risk bridges in the Puget Sound area which has the highest risk of acceleration. Further prioritization will occur as the bridges on this network are retrofitted.
Bridge scour mitigation program
Scour is the removal of soil from around bridge piers and abutments. Flowing water transports soils from around bridge piers and abutments and moves it down stream, leaving the bridge foundations exposed and in some cases undermined. Undermined bridge foundations can compromise the integrity of the structure and in some cases cause collapse. Scour is the leading cause of bridge failures in Washington state and nationwide.
Monitoring and response efforts ensure bridges are safe and haven’t been damage by scour. During routine inspections, the bridge inspectors observe conditions at the bridge piers and abutments as well as the waterway upstream and downstream of the bridge. Bridge scour conditions are recorded in the bridge inspection report. If significant scour is observed, the bridge inspector will call for a repair.
Scour critical bridges are monitored by our staff during flood events. The monitoring is conducted in accordance with a “Scour Plan of Action”, which is a documented plan that has been prepared ahead of time.
If scour has occurred but the damage does not compromise the integrity of the bridge, we will take action to repair the damage. If scour damage compromises the integrity of a bridge, the bridge is closed to traffic until repairs are made.
Rating the condition of bridges
We regularly inspects bridges and categorizes them by condition. The condition scale is good, fair and poor.
- Good: A range from no problems to some minor deterioration of structural elements.
- Fair: All primary structural elements are sound but may have deficiencies such as minor section loss, deterioration, cracking, spalling or scour.
- Poor: Advanced deficiencies such as section loss, deterioration, cracking, spalling, scour, or seriously affected primary structural components. Bridges rated in poor condition may be posted with truck weight restrictions. Poor is the Federal Highway Administration's new rating term for bridges previously described as "structurally deficient."
A bridge in "Poor" condition does not mean the bridge is unsafe for travelers or in danger of collapse. Bridge inspectors have authority to close or restrict any bridge deemed unsafe at any point during an inspection.
The actual number of bridges in "Poor" condition varies as work is completed and bridges are inspected. Depending on inspection schedule timing, a bridge with completed work may remain on the list until the next inspection is completed. The list is updated twice a year, in January and July.