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March 26th, 2014 MARTY SMITH | Dr. Know
 

Dr. Know: A Bridge Too Low?

Why does the new light-rail bridge have less vertical clearance than other bridges?

drknowILLUSTRATION: Hawk Krall
Why is it that the new Duniway/Cascadia/Tillicum/Wy’east bridge has a lower deck and less vertical clearance for ships than the two immediately adjacent bridges, the Ross Island and the Marquam?

—Tom

Just in case you haven’t been breathlessly following the pulse-quickening twists and turns of the TriMet bridge-naming process (I know my readers are not exactly Portland’s leading receptacles of civic pride), the four clunky-ass names catenated together above are the finalists for official moniker of the new light-rail bridge. And man, do they suck.

If I had more civic pride, I might have tried to stop them. But just because I couldn’t pull my proboscis-like tongue out of a gin bottle long enough to attend the (horrible) public-comment hearings where such decisions are made doesn’t mean I can’t answer your question, Tom.

As you may recall from the recent Columbia River Crossing foofaw, the primary driver of a bridge’s height is not how cool it looks, or how much fun it would be to pee off of it on a windy night. It’s how easily big corporations upstream of that bridge can fit their giant profit-boners under it.

For example, if my business model involves having the Washington Monument shipped in by barge twice a year so I can wax it, I can make a case that any new bridge should accommodate that clearance need.

When TriMet was designing the bridge, it polled the maritime businesses operating in the area and concluded they could all live with a bridge around 77 feet high, so that’s how tall it is.

When the Ross Island (1926) and Marquam (1966) bridges were built, however, there were massive shipyards roughly where the South Waterfront is now. They’re not around anymore to ask, but one presumes these businesses’ navigational-clearance needs drove the 130-foot height of those bridges.


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