avatarJoAnn Ryan

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Travel & Photography

Seattle’s Floating Bridges are a True Modern Marvel of Civil Engineering

Learning about and exploring one of Seattle’s iconic landmarks

A sweeping twilight view of Lake Washington and the floating I-90 twin bridges (anyone notice anything else interesting in the sky?)— all photos by JoAnn Ryan

I first began to wonder about them as I gazed out from a cozy loft high up in the Seattle suburbs where I’m spending a month house and pet sitting. From this vantage point, I have an impeccable view of the belly portion, if you will, of sprawling Lake Washington — the picturesque body of water that hugs the eastern edge of the city. The water lies calm and tranquil as small waves lap lazily at the shoreline. To the south slightly is Mercer Island and directly across is the city of Bellevue.

View of Bellevue, WA from Seattle

Slightly to the south, as well, are two bridges, not just one as I’d initially thought, that make up the I-90 connection between Seattle and Mercer Island, known as the Lacey V. Murrow Memorial Bridge (eastbound) and the Homer M. Hadley Memorial Bridge (westbound).

“The (Murrow) bridge is an official landmark of the city of Seattle, as well as a National Historic Civil Engineering Landmark.” (*²)

Day or night, at any random hour of the day, I might peek out and see how things look, given the shifting light in the sky — there isn’t a single time yet where I haven’t found the view more beautiful than the last — but I’ve also, many times, stared out in vast wonderment at those bridges. They sure didn’t look like any I’d ever seen before.

A window view of Lake Washington and the two bridges

Most of the time bridges rise up over the water and have certain more or less common characteristics, like an arch bridge, suspension bridge, cable bridge or truss bridge. By the way, if you are looking for an interesting and well-written overview on bridges, check out this article by Chris Woodford via Explain that Stuff: How bridges work. From the simple wonder of a fallen tree over a space, or a basic beam bridge like the one below, we as a society have come a long way, baby, when it comes to so many things, including bridge building.

A simple beam bridge and a couple of fallen log bridges in the Seattle backwoods

These days, all across the world, millions of people pass onto bridges designed by a pool of talented bridge engineers, often called force balancers, and thus movers, shakers, and travelers like you and me are able to safely get from one place to another all day and night.

Getting back to the I–90 bridges specifically, I wondered at their noticeable flat quality as they hugged against the water, almost as if they seemed to be literally floating on the lake’s surface. Turns out, that’s just exactly what they do. Each are known as a floating bridge.

Floating bridge? What the heck is that and how does it work?

Glad you asked.

Pontoons are the answer. Many of them. I know. I know. What do you typically think of when you think of a pontoon? Don’t know about you, but I think of a bunch of partiers with beers in their hands and party music playing, or perhaps a bunch of hearty fishermen, or women, out on a lake somewhere — they can certainly be women, or trans, or whatever the heck they want to be. We just live in that kind of world now. Wonderfully so.

“On the pontoon…”

Remember that crazy song? I sure do. Who can forget it? I can’t. I had a friend who loved it and wanted to play it all the time when it first came out. For me, it proved to be great practice in being accepting and not being completely annoyed with otherwise lovable people and their questionable taste in music. (Sorry, I know a lot of people probably just LOVE that song).

Anyway, luckily the pontoon system, when it comes to floating bridges, goes far beyond beer and fishing.

According to this article by John Caldbick at HistoryLink.org, the technology is as least as old as Marcus Aurelius (121–180 C.E.) and most likely much older than that. Pontoon bridges have been most commonly used by the military to work as temporary bridges wherever they are needed.

Building off this knowledge, the current technology applied to the Seattle floating bridges was the brainchild of civil engineer Homer More Hadley (1885–1967) who first proposed the idea back in 1920. A lot of people thought he just might be crazy or a “screwball”(*¹). In fact, in 1930 while the plans for the bridge were going through its approval process, The Seattle Times had declared that Lake Washington would be destroyed and called on citizens to ‘PREVENT THIS WANTON DESTRUCTION!’

No matter what kind of nutty idea a person gets in their head though, there’s almost always someone around who will support us. Just look at Charlie Manson or Jim Jones. Ok, terrible examples.

A much better example is Lacey V. Murrow (1904–1966), the older brother of famed journalist Edward R. Murrow, who was then highway director for the state of Washington. He thought Hadley’s idea was pretty ingenious. Another example is Mercer Island businessman George W. Lightfoot, often called ‘The Father of the Bridge’ who also advocated to have the project go through. And thus, construction got underway in 1938, which helped put many depression era workers back in a job, and by 1940 the bridge was complete.

Funding for the bridge was partially paid with a toll of 25 cents. Don’t you wish all tollways were still this cheap?

Hadley floating bridge pontoon

So how exactly does a floating bridge work? The original bridge consisted of 25 sizable pontoons made of concrete reinforced by steel and connected to each other with huge bolts. The pontoons were then anchored to the bottom of Lake Washington, which at some depths reaches more than 200 feet.

“A long list of environmental factors needs to be taken into account,” according to this article on Discovering Washington State, “including, among other things, wind direction and strength, water depth and currents, the type of bottom soil, and the nature of the land on each bank.”

Upon completion in 1940, Governor Clarence D. Martin was the first person to drive over the bridge and pay the 25 cent toll. This act, I’m sure, helped instill the safety of the bridge into people’s minds and it’s not difficult to imagine there wasn’t more than one person who thought, despite Martin’s apparent favorable approval, well heck, if the thing is gonna fail, might as well take down a bureaucrat. C’mon now, you know some people were thinking it.

Luckily everything went swimmingly, or not. The bridge came in at just over a mile in length, making it the longest floating structure in the world until the completion of the new and improved Evergreen Point Floating Bridge in 1989, which lies just a few miles to the north on Lake Washington as well. The construction of this bridge was covered by the Travel Channel: World’s Most Extreme Bridges — SR 520 Floating Bridge.

As many Seattle residents will be well familiar already, eight pontoons of the Lacey V. Murrow Memorial Bridge sank in 1990. Coverage of the sinking of the bridge was caught on camera, of course, in dramatic fashion, via such broadcasts as this one from King 5 News of the Old I-90 Bridge Collapse. However, the bridge was closed and under construction at the time and so thankfully no one was injured.

This planned renovation resulted in the update of the old Murrow bridge to handle one way traffic and the addition of the Hadley bridge to handle traffic headed the other direction.

Of course, as human beings, no matter what we achieve we always have the desire to move on to bigger and better things. For several years now, engineers have been working on running a light rail train over the floating bridges. It seems that where there is a will there is often a way and thus this idea will soon see the light of day.

I knew I couldn’t leave the Seattle area without one final exploration of these iconic bridges. On the day before I flew out of SeaTac Airport, I decided to take one last walk and check things out.

Murrow Bridge view from Lakeside Ave.
View of floating I-90 bridges via Day Street Park

From Day Street Park on Lakeside Avenue, where many ducks and geese can be seen hanging out (just watch out for the mass amounts of bird poop when walking) a great workout may ensue by climbing up all the stairways to reach Lake Washington Boulevard.

Stairways near the floating bridges

As can be seen in many places throughout Seattle, I did observe several tent sites where the homeless have set up their camps in wooded areas. This is currently a huge problem for the city of Seattle — mass amounts of homeless people and what to do about it. Even though I took photos, I’ve chosen not to post them.

At the top of the series of stairways there is a monument dedicated to the Murrow bridge.

Murrow Bridge and Mount Baker Tunnel monuments

Here’s a live view from the top. On the right is the Murrow bridge and on the left is the Hadley bridge.

Live photo of I-90 floating bridges

Another interesting thing I observed is that just prior to the start of the bridges there is a series of tunnels known collectively as Mount Baker Tunnel. Over this tunnel system is built many homes that seem quite stately in nature. Here’s a question: would you want your house built over a tunnel? I just don’t know.

Mount Baker Tunnel and the houses built over it

On the eastbound Hadley bridge is a path where people can walk and bike across. No, I didn’t walk the whole thing. It was a chilly February day, after all, and my nose dripped more and more with each step. But I was determined to at least walk out to the flat part of the bridge. Here I observed all the motion rushing by, including cars, semis, emergency vehicles with their lights on, school buses, transit buses, and a few bicycle riders. All rushing by me in a blur.

Emergency vehicle on Hadley floating bridge

No one else seemed crazy enough to be walking out here in the middle of February — it ended up being quite windy and bone-chillingly cold toward the middle — and I’m sure more than one person may have thought I was completely nuts, but I’m ok with that.

I do wonder though, how many people who rush across these bridges every day — getting to work, school, or other such places — ever stop to marvel at the fascinating technology or say a silent thank you to all those talented bridge engineers who continue to work tirelessly every day to ensure the rest of us get safely and conveniently from one place to another.

Well, I for one sure did on that, my last day in Seattle. Here is one last look at the Lake Washington shoreline from the Hadley bridge.

View of Lake Washinton shoreline from Hadley Bridge

Sources for information and further reading:

  1. Lake Washington Floating Bridge (Lacey V. Murrow Memorial Bridge) — HistoryLink.org
  2. Washington State Floating Bridges: The Longest In The World — Discovering Washington State
  3. PCAD — State of Washington, Highway Department, Lake Washington Floating Bridge #1, Seattle-Bellevue, WA

This story is part of the February writing challenge on bridges here at Globetrotters. For more great stories check out Serhii Onkov’s account of ruined bridges in Ukraine:

As well as Purbita Chakraborty’s lovely bridge story:

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