Crews building the new SR 520 bridge on Lake Washington reached the milestone this week as they moved the bridge’s last three massive concrete pontoons into place. The pontoons form the structural spine of the bridge in the US state of Washington.
Pontoons B, C and D were towed from an east-end moorage near Medina to their permanent location at the new bridge’s west end, near Seattle. Bolted together, the three pontoons gave the appearance of a giant barge – more than 305m long. Tall columns and a new roadway have already been built on top of the three pontoons, which together form most of the new floating bridge’s west high-rise section.
“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, the Washington State Department of Transportation’s administrator of the SR 520 bridge replacement and high-occupancy vehicle programme. “It’s an exciting day for everyone involved in the project.”
Just one of the total 77 pontoons now needs to be positioned. 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 11,000t and 110m 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-car pool lane in each direction. It will also have wide shoulders and a bicycle and pedestrian path.
