Seattle Floating Bridges –  Do They Really Float?

Can a concrete and steel bridge really float on water?  The Seattle Floating Bridges have done so for decades! You say:  ” But it just does not seem possible!”  Let’s take a quick look at why and how it is possible, OK?  You’ll enjoy this little “trip” down the memory lane of Seattle Floating Bridges.  🙂 Why would the city fathers ever consider building Seattle floating bridges in the first place?  Let’s look back at the reason and a brief history.

I recommend that you read my blog about the Seattle Ferry Boats to give you an idea of their history as the two of them are related to each other.  Makes interesting reading too.

Now, in your mind’s eye, go back to the late 1800’s when there were no paved roads, no large bridges, no cars or trucks.  People and goods were transported either by ship, boat, or ferry over the water.  On land it was by carts, or large wagons.

The rather small island of Mercer Island (see map as it looks like today)  was in need of regular transportation to and from the island to the center business area of Seattle.  It was mainly accomplished by canoe or rowboats, carrying other types of goods and if you were fortunate, you could “hitch” a ride.

Seattle on Left Mercer Island in Center Bellevue-Kirkland-Redmond on Right

Seattle on Left Mercer Island in Center Bellevue-Kirkland-Redmond on Right…click for larger view

One man by the name of James Mortie came to the area with it’s first powered vessel way back in 1890.    Because of his success, others jumped on the “power vessel” wagon and made small fortunes by carrying goods and passengers over Lake Washington.

Typical circa 1900 steamer between Seattle & Mercer Island

Typical steamer used between Seattle & Mercer Island Circa 1900…click for larger view

Seattle’s Entrepreneur Spirit


Anderson was a real entrepreneur,  a spirit which still dominates the Seattle population.  He began shipbuilding  in Kirkland.  His first vessel was his famous 95 foot “Atlanta.”

Within the next few years, he became very successful, especially when the year 1909  came around and the Alaska-Yukon-Pacific Exposition came to the area that is now called “The University of Washington” or known by the locals as :  The U District.

However, Anderson was quick to recognize that his great fortunes came about by sightseeing and cruise tours, not ferrying passengers.   He decided to concentrate only on cruises.

Since progress continued on land as well as on sea, roads were being built throughout Seattle and all over Mercer Island.  So the idea of building a bridge from Mercer Island to Seattle began to take shape.

It was short lived though, when in 1929, the stock market crashed, sending all hopes of a bridge to the bottom of Lake Washington. However, 10 years later in 1939, the bridge idea once again was revived and in 1940 the Mercer Island floating bridge was officially opened for traffic.

Seattle Floating Bridges to Mercer Island Opening Day July 3, 1940 Some chose to wear life vests as they crossed!

Seattle Floating Bridges to Mercer Island Opening Day July 3, 1940 Some chose to wear life vests as they crossed!…click for larger view

Opening Day 1940

Opening Day 1940…click for larger view

How Was It Built ?

Originally named Lacey V. Murrow Bridge, it was the longest and largest floating bridge ever built.  Way back in 1922 it was deemed necessary as the traffic coming through Snoqualmie Pass (snow qual me) over what is now I-90, was the only road that was open year round.

It was loaded with heavy traffic that needed to get to downtown Seattle and the shipping docks.  Detours were set up to re-route traffic through  city streets and residential areas.   From the North Bend area, to Seattle was about 42 miles.  Fourteen of which went through city streets. A bridge needed to be built and quickly!

At first there were ideas thrown around about a suspension bridge.  But the cost was staggering.  Then Homer Hadley, a designer, proposed a floating bridge made of concrete and steel.  It’s cost?  It was a mere  1/5 th of the cost of a suspension bridge. But how to keep it stable was an issue that now surfaced.  An anchor system of concrete and cable ties to the underside of the bridge was considered.

Will It Float Away?


However, because of the soft lake floor, it did not sit well with anyone.  From the water surface to the lake floor was some 400 feet with another 150 or more feet going through the soft lake mud to the more firmer soil.

That idea was discarded in favor of building concrete pontoons for the roadway to ride on.   Once the contractor was decided upon, the pontoons were built on Harbor Island.  As each section of the pontoons were completed, they were towed across Elliott Bay through the Ballard Locks and into position on Lake Washington.

Each section was some 350 feet long, 60 feet wide and more than 14 feet deep, allowing the road surface to rise just above the water level.  Each had 8 separate “cells” in 12 watertight compartments with  6 to 8 inches of roadway surface on top. In order to accommodate ships, it had a draw span section that was successfully used until  the early 1990,s  when the draw span was replaced with fixed-in-place, pontoons.

Each end of the floating bridge was raised and restructured high enough,  to allow marine traffic to pass underneath.

But What About the Open Water “Bulge?”

Note the "ramp" that can take you up & into the open hole.

Note the “ramp” that can take you up & into the open hole. museumofhistory&art

What of the bulge?  I can recall as I was growing up living in Bellevue, that my dad would from time to time, take the family across the bridge into Seattle.  Just as we began to cross the bridge from the Bellevue side, there was this “ramp” looking area that, if a driver was not paying attention to, could drive up and over right into the lake itself!  Each time we went by it, it scared the stuffing out of me.  🙁 Needless to say, no one ever  knew whether or not anyone ever went up and over it…..down into the deep, cold, dark  200 or 300 feet deep waters under the end of the  bridge.  NOT a pleasant thought!

A Very Sad Note.

It was not until years later (around the early 1980’s) when the above mentioned renovation of the bridge began.   As  one of the dredging companies working on the bridge project began it’s work, a car that had been missing for more than 20 years, was pulled to the surface. It’s occupant?……….A young teenage girl coming home at night after her high school prom dance.  She was still inside the vehicle.   🙁

Today’s Seattle Floating Bridges

Today, though, the Seattle Floating Bridges are unique in themselves.  In fact, because of it’s success, the Evergreen Floating was built just north of the Mercer Island Floating Bridge. Take a trip across it, the view is great as you are practically “walking on water” as you ride along!

Splish Splash I Was Taking A Bath…..All On A Saturday Night

Having made the “crossing” literally thousands of times, it never ceases to amaze me when my wife and I cross on a stormy day. Because of the bridge design, it’s laying flat in the water, it acts much like a windbreak where you can see and feel the spray from the windward side of the bridge with the lake water splashing and blowing up against your car, and at times, watching as  waves cross over the entire bridge!  And at the same time on the opposite side of the bridge, it is almost as smooth as glass! It is something you’ll love to experience!

Are you a brave one?  Then try driving the bridge with your windows down during that same windy crossing!  You’ll love it!

What the bridge looks like today.

What the bridge looks like today. JoshuaTrujilloPhotoP.I.   …click for larger view

It's like "walking" on water!

It’s like “walking” on water! JoshuaTrujilloPhotoP.I.   …click for larger view


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