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SR 520 - Floating Bridge and Landings Project: Pontoon Tracking and Bridge Assembly

Updated: May 21, 2015

Follow along with WSDOT as we continue to build, tow and assemble pontoons and make progress on the new SR 520 floating bridge on Lake Washington. 

Floating Bridge Assembly 
rendering of bridge assembly status
  Diagram showing the construction status and approximate configuration of elements of the new floating bridge. Last updated May 21, 2015.

View the full, printable graphic . (pdf 1.5 mb).


Low-rise roadway deck includes pre-cast deck panels being constructed in Kenmore.
- 667 out of 776 pre-cast deck panels have been constructed. 512 of 776 have been set.

High-rise roadway deck includes girders and cast-in-place deck.

- 16 out of 23 cast-in-place deck spans have been constructed.
- 331 out of 331 girders have been constructed. 303 of 331 have been placed.

The number of columns shown in the graphic is a representation of the total number of columns.

- 611 out of 772 columns have been constructed.

Pontoon count:
    -Current number of pontoons on Lake Washington: 77.
    -Total number of pontoons constructed to date: 77.
    -Pontoons currently under construction: 0.

Pontoon towing update

  • On Thursday, April 9, the last three pontoons needed to construct the new floating bridge arrived on Lake Washington. No other pontoon arrivals are planned.

Pontoon transit route

Pontoons for the new floating bridge were constructed at two different sites in Washington state: Aberdeen and Tacoma. We completed pontoon construction in Tacoma in December 2014 and in Aberdeen in March 2015. After the pontoons were completed and ready for assembly, tugboats towed them to Seattle. The trip from Aberdeen to Seattle is nearly 260 nautical miles .

Pontoons were visible from multiple locations along the Ship Canal. Many of the photos on our Flickr set were taken from locations on this map of suggested viewing locations  (pdf 2.5 mb). 

Build your own pontoons for the floating bridge

The floating bridge pontoons represent a key milestone in a critical safety project. Using the printable pontoon templates linked below, you can build your own bridge that follows our progress with the construction, transport and final positioning of floating bridge pontoons.

  • As we complete the construction of each pontoon and bring them to Lake Washington, we will post new templates here. Each pontoon is labeled according to its location within the final bridge structure.
  • For each pontoon, download and print the template file (each pdf is approximately 400 kb), cut along the indicated lines, and then fold your pontoon for final construction.
  • We will maintain the links for each pontoon template, so that you can catch up with any you might miss. Templates will be added as pontoons arrive on the lake.

Aug. 11, 2012: Pontoon V
Aug. 14, 2012: Pontoon W
Aug. 18, 2012: Pontoon VNW
Aug. 19, 2012: Pontoon VSW
Aug. 22, 2012: Pontoon U
Sep. 22, 2012:  Pontoon VNE and Pontoon VSE
Sep. 30, 2012:  Pontoon UNE and Pontoon USE
Feb. 2, 2013:  Pontoon UNW and Pontoon USW
May 15, 2013: Pontoon T
Jun. 7, 2013: Pontoon A
Jul. 22, 2013: Pontoon TNW
Jul. 23, 2013: Pontoon TSW
Aug. 27, 2013: Pontoon TNE and Pontoon TSE
Aug. 30, 2013: Pontoon S
Oct. 17, 2013: Pontoon BSE
Oct. 20, 2013: Pontoon Q
Oct. 23, 2013: Pontoon R
Oct. 29, 2013: Pontoon BSW
Dec. 9, 2013: Pontoon SNE
Dec. 10, 2013: Pontoon SSE
Dec. 11, 2013: Pontoon SNW
Dec. 12, 2013: Pontoon SSW and Pontoon RSW
Dec. 13, 2013: Pontoon RNW and Pontoon RNE
Dec. 14, 2013: Pontoon RSE
March 13, 2014: Pontoon PSW and Pontoon PNW
April 13, 2014: Pontoon P
April 16, 2014: Pontoon O
May 4, 2014: Pontoon M  and Pontoon N
May 8, 2014: Pontoon QNW , Pontoon BNW  and Pontoon DSW
May 9, 2014: Pontoon QSW  and Pontoon OSW
May 10, 2014: Pontoon ONW
May 11, 2014: Pontoon NNW and Pontoon NSW
May 12, 2014: Pontoon MNW
May 13, 2014: Pontoon MSW
Aug. 11, 2014: Pontoon B  and  Pontoon C
Aug. 16, 2014: Pontoon D and Pontoon E
Sept. 17, 2014: Pontoon BNE
Sept. 18, 2014: Pontoon CNW and Pontoon CSW
Sept. 22, 2014: Pontoon DNW
Sept. 23, 2014:  Pontoon ESW
Sept. 24, 2014:  Pontoon ENW
Sept. 25, 2014: Pontoon KNW
Oct. 1, 2014: Pontoon LSW
Oct. 2, 2014: Pontoon KSW
Oct. 3, 2014: Pontoon LNW
Oct. 4, 2014: Pontoon I , Pontoon J , Pontoon GSW and Pontoon GNW
Oct. 10, 2014: Pontoon L  and Pontoon K
Dec. 5, 2014: Pontoon INW and Pontoon ISW
Dec. 6, 2014: Pontoon HNW , Pontoon HSW , Pontoon FNW and Pontoon FSW
Dec. 7, 2014: Pontoon JNW and Pontoon JSW
April 9, 2015: Pontoon G, Pontoon H, and Pontoon F


Types of pontoons

The new SR 520 floating bridge will be supported by three types of concrete pontoons:

Longitudinal pontoons (21)

These are the largest pontoons at approximately 360 feet long. They form the backbone of the bridge and support the roadway superstructure.

  • Constructed in Aberdeen facility
  • Weight: 11,100 tons

Cross pontoons (2)

These mark the ends of the floating bridge section and the transition to the East and West Approach structures.

  • Constructed in Aberdeen facility
  • Weight: 10,100 - 10,550 tons

Supplemental stability pontoons (54)

These smaller pontoons help stabilize and support the weight of the new floating bridge by joining to larger longitudinal pontoons.

  • Constructed in Aberdeen facility (10) and Tacoma facility (44)
  • Weight: 2,500 - 2,820 tons