Friday, August 10, 2012 - Page updated at 10:27 PM

Putting together the 520 bridge

Putting together the 520 bridge

Reporting by Mike Lindblom

Graphic by Mark Nowlin

On Saturday evening, a tugboat will carefully tow the first of 77 pontoons through the Ballard Locks, then through four drawbridges to the east end of the Highway 520 bridge. These pontoons, built in Aberdeen and Tacoma, will hold up the world's longest floating span, crossing 7,710 feet of Lake Washington east of Seattle. The floating section of the new six-lane, $4.65 billion highway is scheduled to be finished by the end of 2014.

One of several primary pontoons is floated out of the Port of Grays Harbor Monday, due to become part of the new SR 520 floating bridge.

Dean Rutz / The Seattle Times

The route to Lake Washington

Between 6 and 9 p.m. Saturday, the first of 77 new Highway 520 bridge pontoons should reach the Ballard Locks. The pontoon, 75-feet wide plus wood bumpers to protect it, will squeeze through the large 80-foot lock. The public can watch from Commodore Park, south of the locks.

The largest pontoons will be shipped one at a time from Grays Harbor along the coastline, through the Strait of Juan de Fuca to Puget Sound, through the locks and into Lake Washington.

The work on Lake Washington

Workers on the lake are testing bridge anchors, and concrete will be poured in September for the first of two piers at the east highrise. Road decks will be fabricated in Kenmore.

1. The east-end cross pontoon, to arrive early next week, will be positioned and anchored in place.
2. Stability pontoons will be fastened to the longitudinal pontoon that arrives Saturday.
3. The pontoons will then move into position and connect to the cross pontoon.
4. The process repeats as more pontoons are brought from Aberdeen and Tacoma.
5. Pontoons will be connected moving westward.
6. Later, pontoons will be anchored at the west end and connected moving eastward.
From Aberdeen

Longitudinal pontoons: 21

Cross pontoons: 2

From Tacoma

Supplemental stability pontoons: 44

Aberdeen will make 10 more supplemental pontoons for a total of 54.

Source: Washington state Department of Transportation