I-5 - SR 18 to S. 288th Street Seismic Retrofit - Completed February 2015


Contractor crews seismically retrofitted four bridged sections of Interstate 5 from State Route 18 in Federal Way to South 288th Street in Kent.

The retrofitting is necessary because I-5 was built more than 50 years to seismic standards that are out of date. As a result, sections of I-5 are vulnerable to earthquake damage.

Retrofitting consists of fitting large steel sheets, called jackets, around the existing columns that support the overpasses. This helps prevent the columns from collapsing in the event of an earthquake. 

Crews also added supports and stops to the crossbeams to provide a wider base for the bridge girders and prevent them from sliding.  
The overpasses retrofitted are located at:

  • SR 18/I-5 interchange
  • South 336th Street
  • Military Road South
  • South 288th Street

Learn more about how a seismic retrofit is completed.


How you benefit

Improves safety
This project helped reduce potential damage to I-5 bridges in the event of an earthquake by strengthening the columns and crossbeams that support the bridged sections.

Economic incentive
This project is part of our seismic retrofit program established in 1991 to help make bridges safer. I-5 is the backbone of the Washington economy. Ensuring that the bridges on I-5 are seismically retrofitted reduces the risk that portions of I-5 will collapse in an earthquake, allowing freight and people to keep moving.


Pre-Existing Funds (PEF): $6,344,000
Total: $6,344,000


Contact us
WSDOT communications
15700 Dayton Avenue North
Seattle, WA 98133


Project map of the work area.
View larger map

Bridge columns at S. 288th St. to be retrofitted.
Four overpasses similar to this one at S. 288th Street were retrofitted.