New SR 520 floating bridge reaches milestone

Construction of the new State Route 520 floating bridge across Lake Washington reached another milestone this past weekend with the first permanent placement of a bridge pontoon on the lake’s west side.

The 240-foot-long, 10,000-ton Pontoon A, with large roadway-support columns mounted atop its deck, will be the new bridge’s western-most pontoon. Pontoon A and Pontoon W, now anchored near the lake’s eastern shoreline, will bookend the floating bridge’s 21 longitudinal pontoons. The latter structures, each 360 feet long, are the floating bridge’s primary support.

“This pontoon placement essentially represents the start of bridge assembly,” said Julie Meredith, director of the SR 520 Bridge Replacement and HOV Program for the Washington State Department of Transportation. “In coming months, the public will start to see a new floating bridge take shape as we align and connect other pontoons in between A and W.”

On April 19, crews towed Pontoon A from its moorage site near Medina to its permanent location about 50 feet north of the existing floating bridge’s west approach, near Madison Park. The pontoon will be secured in place with large steel cables attached to anchors secured to the lakebed.

Fifty-two of the new bridge’s 77 pontoons have been constructed so far, with 34 now on Lake Washington. The new, six-lane bridge is scheduled to open to traffic in spring 2016.

Pontoon A’s permanent location will obstruct the west navigation channel running beneath the existing SR 520 floating bridge. As a result, the 206-foot-wide boating channel will reduce in width to 120 feet. The narrower channel will be marked by traditional red and green buoy markers.

The temporary channel configuration, approved by the U.S. Coast Guard, will be in place until additional pontoons are joined with Pontoon A. The west navigation channel’s vertical clearance of 45 feet will not change.

In addition, once Pontoon A is secured to its permanent anchors, a new exclusion zone for water craft will be activated. The off-limits area will be marked by six white buoys located north and south of the pontoon and with a sign on each end of the pontoon. The white buoys represent the locations of anchor lines and it is dangerous for boats to pass between the sign and the buoys.

The floating bridge’s east navigation channel remains closed to boats due to construction near the Medina shoreline, except on special boating dates and holidays. Boats more than 45 feet tall must use the floating bridge’s drawspan by calling 206-440-4490.

The new floating bridge, with a higher, 70-foot clearance beneath its east navigation channel, will not have a drawspan.

More information about the SR 520 Bridge Replacement and HOV Program can be found online.

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