There’s been bridges in the news lately.

First and foremost is of course the incredible bridge collapse in Minneapolis. I’ve been on I35-W several times in my life, and even gone over the bridge that collapsed. The Mississippi River is a major landmark in the Twin Cities area and naturally there are several spots where there’s bridge crossings over it. My heart and thoughts go out to all the friends and families who are right now hoping beyond hope that their missing loved ones are simply off on a bender somewhere and not in the murky bottom of the river (as I write this, there’s a couple of dozen people still reported missing).

The other bridge that has been in the news is here in Seattle. Starting August 10th, and running until the 29th (earlier if we’re lucky, later if we’re not) the State DOT is doing a great big remodel/repair job on Interstate 5- right through downtown Seattle. This project will take the freeway from five lanes through most of the project down to two or three, and it is going to run 24 hours a day until it’s done.

130,000 cars use this section of freeway, from Spokane Street to I-90, each day. Including me. My place is just west of the junction of I-5 and I-90, and I work down in Auburn to the south, so when I come home I usually drive this section.

It’s kind of ironic that this project is happening because some months ago, I had thought about writing a bit for this blog. I was driving to work and, having recently read one of Luis’s blog entries about earthquakes (he lives in Japan so there’s a lot), I was thinking of just how incredibly dependent on bridges the city of Seattle is.

There’s really not a major transportation arterial into Seattle that doesn’t have a significant bridge, or several, along its route. I-5 has not only the massive Ship Canal Bridge up north of downtown, but also this stretch of road that they’re repairing. I-90 has the floating bridges across Lake Washington, 520 has a floating bridge, and Highway 99 has the Aurora Bridge. Even the smaller routes from the south all have bridges.

For whatever reason, when they designed I-5, they made a long section of it a bunch of bridges. I suspect it was just easier to build it that way since it curled along a hillside. Here’s an excellent map of the affected area, along with suggested alternate routes:

(click for a full size graphic)

What you can’t see in that graphic is that the closure section- the dark red up section- is perched along the side of Beacon Hill. Seattle has several big hills; it’s definitely NOT a flat city, even though it’s at sea level at its lowest point. The highest point in Seattle (known as- shockingly- High Point) is over 500 feet high, and many of the hills go from sea level right up to a couple two or three hundred feet pretty quick.

Here’s a link to a picture of the I-5 and I-90 interchange. You can see all the trees along the eastern edge of I-5; those aren’t there as a greenbelt. Well, it is a greenbelt, but it’s not a greenbelt because they wanted a greenbelt; it’s a greenbelt because it’s too steep to build on.

If you look carefully at I-5, or click to zoom in on the picture, you can see how there’s little lines across I-5. Those are expansion joints, because that whole section of roadway is built up on pilings. You can call it one long continuous bridge, or think of it as a series of bridges.

What I was thinking as I drove in to work was just how totally screwed Seattle is if there’s ever a REALLY big earthquake, the kind that drops a significant number of the bridges in an area to the ground or water below. The city is extremely hemmed in by water.

Anyway, just musing. When you have a 35 to 45 minute drive to work each day, you have a lot of time to think, and this is some of the crap that runs through my brain. Well, when I’m not thinking about how to score with that hottie at the coffee shop or about last night’s Mariners game (another win! Yay!)