SEATTLE, WA Crews building the new State Route 520 floating bridge on Lake Washington reached a significant milestone as they moved the bridge's last three massive concrete pontoons into final position. The pontoons form the structural spine of the world's longest floating bridge.

Crews towed pontoons B, C and D from an east-end moorage near Medina to their permanent location at the new bridge's west end, near Seattle, Washington. Bolted together, the three pontoons gave the appearance of a giant barge - more than 1,000 feet long. With tall columns and new roadway deck already built atop them, pontoons B, C and D together form most of the new floating bridge's west high-rise.

"With the final three longitudinal pontoons now in their permanent location, you can actually see this great new bridge stretching end to end across the lake," said Julie Meredith, Washington State Department of Transportation's Administrator of the SR 520 Bridge Replacement and HOV Program. "It's an exciting day for everyone involved in the project."

Within a few weeks, crews will tow Pontoon A back into position and connect it to Pontoon B. Pontoon A is one of two "cross" pontoons that bookend the new floating highway. In between are the bridge's 21 longitudinal pontoons - each 11,000 tons and 360 feet long. Fifty-four smaller, supplemental pontoons flank the jumbo pontoons to give the bridge added support and stability.

When it opens to traffic in spring 2016, the new floating bridge will have two general-purpose lanes and one transit-carpool lane in each direction. Built to withstand stronger windstorms and wave action, the bridge also will have wide shoulders for disabled vehicles and a 14-foot-wide bicycle and pedestrian path.

All major improvements to an expanded, six-lane SR 520 from Medina to I-405 already are complete. Meanwhile, WSDOT contractors are now building a three-lane, fixed-pier bridge that will carry westbound traffic from the new floating bridge to Seattle's Montlake area. This West Approach Bridge North, constructed to modern seismic standards, will also extend SR 520's new regional bicycle-pedestrian path from the Eastside to Seattle.

Other planned improvements to SR 520's Seattle corridor, including a new Portage Bay Bridge, highway lids in the Montlake and Roanoke neighborhoods, and the south (eastbound) half of the west approach bridge, await state funding.