Low-rise deck complete for new SR 520 floating bridge

Seattle — Construction workers completed installation of the low-rise roadway deck for the new State Route 520 floating bridge on Lake Washington, marking another major accomplishment for the Washington State Department of Transportation en route to opening the new bridge to traffic early next year.

Using a barge-mounted crane, crews lowered the last of 776 precast, interlocking roadway deck sections onto the bridge. The setting of this final, 100-ton deck section came less than a year after crews set the first low-rise roadway section on Sept. 8, 2014.

“With the low-rise roadway now in place, the new bridge is really taking shape,” said Denise Cieri, WSDOT deputy administrator for the SR 520 Bridge Replacement and HOV Program. “And to think – three years ago there was nothing but water where this impressive structure now lies.”

At 7,710 feet in length, the new bridge is 132 feet longer than the Evergreen Point Floating Bridge, which for 52 years has been the longest floating highway in the world. The new structure, built to withstand stronger winds and wave action, includes HOV lanes in both directions, shoulders for disabled vehicles, and a 14-foot-wide path for bicyclists and pedestrians.

All 776 of the new bridge’s roadway deck sections were constructed at a lakeside facility in Kenmore. Barges delivered them to the bridge construction site on Lake Washington. Most of the bridge’s main structures and components are now assembled in their final positions on the lake. From the top down, they include:

• 331 concrete and steel girders that support the roadway deck
• 771 concrete columns on which the girders lie
• 77 concrete pontoons that keep the entire structure afloat (the 21 largest ones are 360 feet long and 11,000 tons each)
• 58 anchors, some weighing 450 tons, that hold the floating bridge in place.

Crews continue to build and place the final sections of the new cast-in-place concrete bridge deck at the west high-rise near the Seattle shoreline. Additionally, a substantial amount of work remains to be completed to commission the bridge before traffic can be switched over to the new structure. Crews continue to install more than 300 miles of electrical wire and various electronic components and sensors along the bridge’s entire length – all electronically linked to a new bridge maintenance facility in Medina and the WSDOT northwest regional office in Shoreline.

Other work that remains to be completed includes installation of traffic barriers, noise walls, lighting, sign bridges, pedestrian railing, and placement of more than 70,000 tons of rock ballast inside the bridge’s pontoons. Extensive inspection and testing will precede the bridge’s opening to traffic, currently planned for spring 2016.

“We’ve come a long way on this project,” Cieri said. “When the bridge opens to traffic next spring, we’ll briefly pause and celebrate with the community. And then we’ll get right back to work on completing the highway’s remaining improvements all the way to Interstate 5.”

The 2015 Legislature passed a measure authorizing $1.64 billion to complete the planned SR 520 improvements from I-5 to Lake Washington – the “Rest of the West.” Those improvements include new, seismically stronger Portage Bay and Union Bay bridges, highway lids in Seattle’s Montlake and Roanoke neighborhoods, and a second bascule bridge across the Montlake Cut.