1962 I-5 and 1919 University Bridges over Lake Washington Ship Canal in Seattle, WA

1919,1933 University: (Bridge Hunter; Satellite)

1962 I-5: (Bridge Hunter; Satellite)

The Lake Washington Ship Canal was built in 1917.

Bridges Now and Then posted
Building Seattle, Washington's, Ship Canal Bridge over Portage Bay, c. 1961. (Seattle Post-Intelligencer)
Chris Evans: Still using rivets.

A construction photo of the trusses getting close to each other

I-5 is the truss bridge on the left and University Bridge is the drawbridge on the right.

Street View

 

Jann Mayer 2013 Photo via BridgeHunter-1962, License: Creative Commons Attribution (CC BY)

2014 Royce and Bobette Haley 2014 Pano via BridgeHunter-1962, they provided many more photos

As with many of our interstate bridges, this one is now falling apart. The parks under both approaches were closed in 2019 because concrete was falling from the bridge! "When asked why the Ship Canal Bridge was allowed to deteriorate, Secretary Roger Millar told the editorial board: 'Because we need to be spending $2 billion a year (on maintenance and preservation) and we’re spending $925 million dollars a year.'...The 182-foot tall structure carries more than 200,000 vehicles a day, and it’s vital to the state’s economy. It has been 22 years since the last major preservation project." [SeattleTimes]

Photo via HistoryLink
Lake Washington Ship Canal Bridge (Interstate 5) under construction over Lake Union, with University Bridge below, 1961.
Courtesy MOHAI (2009.23.57)
"It is a steel truss double-deck bridge, which carries eight lanes of traffic on the upper deck and four reversible lanes of traffic on the lower deck." [Priscilla Long, License: Attribution-NonCommercial-NoDerivs (CC BY-NC-ND 3.0)]

The eight regular lanes go up and over the four reversible (express) lanes.

Street View

The original approaches to the University Bridge were built with temporary wooden trestles. The 1933 rebuild replaced the approaches and doubled the width of the bascule spans. To reduce the weight of the wider deck, the entire deck was replaced with a open-mesh steel deck. So it must have been a "hummer." The use of an open-mesh steel deck was novel in 1933. I cannot reconcile the description of how they added the extra lanes and walkways with the photos I see today. The description says the new lanes and walkways were cantilevered outside of the truss lines. But the photos show only the walkways are cantilevered. [Engineering News-Record]

2016 Patrick Gurwell Photo via BridgeHunter-1919

2014 Royce and Bobette Haley 2014 Photo via BridgeHunter-1919, they provided many more photos

A 12:52 video starts with this bascule bridge  It refers to the this type of bridge as the "Chicago-style fixed trunnion bascule bridge." And the bridge uses pony trusses, which are above the deck as well as below the deck. At 3:00, the video provides details of the trunnion and the pinion gear in action. (The details may not be of this bridge in particular, but the trunnion designs would be similar.) At 3:39, the video describes the BNSF/GN Ballard Bridge. The video revisits the University Bridge at 8:21.