Sound Transit: Public can view plans for new rail trestle

Sound Transit will hold an open house Thursday to show early conceptual plans for replacing a 100-year-old railroad trestle east of Freighthouse Square.

The old creosoted-timber trestle, 30 feet high and about one-third of a mile long, has been in continuous service since the Milwaukee Railroad built it early in the 20th century.

The wooden structure now carries Sounder commuter trains and Tacoma Rail freight trains across an industrial area between the Thea Foss Waterway and the Puyallup River.

Replacing the old, single-track trestle with a concrete, double-track structure was part of the Sound Transit 2 ballot measure that voters passed in 2008. The replacement project is budgeted at $59 million and is to be completed in 2017.

The project includes upgrading railroad signals, reinforcing embankment, making minor street repairs and relocating some utilities.

Planning and engineering are in preliminary stages, with construction scheduled to begin in 2015.

Thursday’s open house is to gather public input on design options.

“We’ll be showing examples only,” Sound Transit spokeswoman Kimberly Reason said. “It’s too early in the planning to have actual designs. Our purpose in having the open house is to share some of these conceptual elements with the public and get their feedback to help us identify what could work best.”

The trestle project will enable Sound Transit to handle planned increases in passenger rail traffic. Amtrak intends to begin using the tracks for seven round trips a day in 2017.

The main technical challenge in construction will be keeping the rail line open while the new trestle is built, said Eric Beckman, Sound Transit’s deputy executive director of business and construction services.

“What we’re looking at now is how to build it one half at a time,” Beckman said Tuesday. “That sort of planning is probably the single biggest challenge in how we accomplish this.”

Another challenge, Beckman said, is that the soil beneath the trestle — fill material deposited on the Puyallup River delta — is unstable. The new structure probably will need to be supported on columns that extend to solid soil 80 or 90 feet beneath the surface, Beckman said.