Alaskan Way Viaduct Is Moving

Earth Changes

October 6, 2003

By Kevin Reece, KOMO 4 NEWS

SEATTLE - Ever since the Nisqually earthquake of 2001, DOT workers have been keeping a close watch on the Alaskan Way Viaduct.

Metal bars, plates and pieces of concrete have fallen from time to time. Workers have also done extensive retrofitting done to hold sinking sections of the bridge in place.

DOT engineers measuring the bridge Saturday said portions of it are still moving.

"The curve is meant to line right up," said engineer George Comstock. "But sometimes they've been moving offset which means that the bridge is moving sideways."

Engineers measure the viaduct every six months. They check expansion joints, take detailed measurements, check gauges placed on existing cracks.

"Now we are noticing that indeed we do have some fresh changes occurring on this bridge," said Comstock.

At one spot it's moved 5/8 of an inch, and it's moved 4 millimeters at another area.

Measurements will all factor into the decision of what to do with the aging span. Officials are still trying to decide if it needs to be replaced - when that might happen - and what will take the viaduct's place.

But the immediate concern is whether its safe right now for its estimated load of 80,000 cars a day.

After another day of measurements DOT engineers said yes.

"At this point we have no reason to believe that the bridge is any less safe than its ever been and its certainly safe for the posted loads that are on it now," assured Comstock.

As for why the bridge continues to move, the cause is officially un-determined. Engineers suspect shifting soil beneath the viaduct or the bridge itself continuing to settle.

The viaduct will be closed Sunday from 6 a.m. until 6 p.m for another round of inspections.