Local Information

Replacement bridge opens on SR 508 near Onalaska

Tuesday, April 2, 2019 - 08:37

Tamara Greenwell, communications, 360-905-2056

Historic pony truss bridge to be relocated in Washington state

ONALASKA – Single-lane travel across the State Route 508 South Fork Newaukum River Bridge, east of Onalaska in Lewis County, will soon be a thing of the past.

A new two-lane replacement bridge is scheduled to open to travelers on Friday, April 5, paving the way to improved safety and mobility for all users of the highway.

In July 2012, the Washington State Department of Transportation put a 7-ton weight restriction and detour in place, in an effort to extend the usable life of the structure by limiting heavy loads from crossing the bridge. A routine inspection in January 2015, determined that overweight loads had continued to cross the aging bridge, accelerating the deterioration of the vulnerable structure.

For the safety of the traveling public and to keep this important travel connection open, a temporary single-lane Bailey bridge was installed across the aging structure in 2015, and was kept in place until the replacement bridge could be built.

"The opening of the replacement SR 508 South Fork Newaukum River Bridge is a win/win for Washington's future and our past," said Project Engineer Joanna Lowrey. "The new structure is more functional, meeting current engineering and safety standards, while the old bridge will be preserved, maintaining a piece of Washington state's transportation history."

Preserving Washington's historic bridge

  • Built in 1930, the original 197-foot South Fork Newaukum River Bridge is one of only 13 pony truss bridges over 50 years old that remain in use on public roadways or recreation trails in Washington.
  • A pony truss bridge allows traffic through the truss, but the top of the bridge is not joined together with cross braces. During the first half of the 20th century, pony truss bridges like the SR 508 South Fork Newaukum River Bridge were often used to span short distances. As concrete girder bridges gained in popularity, pony trusses have become relatively rare.
  • WSDOT conducted a nationwide search and identified a new owner who is committed to preserving the historic nature of the structure, which has served the community for nearly 90 years. The individual plans to keep the bridge in the Evergreen State.

Next Steps

  • On Wednesday, April 3, crews will pave the westbound lanes of the new bridge, and install guardrail and pavement markers.
  • The morning of Friday, April 5, crews will fully open the new bridge to travel in both directions. Paving work is weather dependent and the bridge opening could be delayed if it rains.
  • In April, WSDOT maintenance crews will remove the temporary single-lane Bailey bridge.
  • Later in April, crews will carefully dismantle the historic steel structure for relocation to private property.

Crews will work through fall 2019, doing landscaping work to complete this $8.5 million project.

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