A mistake of five inches forced a private contractor to tear down a ramp it was building on Seattle's Spokane Street Viaduct, just as progress was becoming visible to aggravated motorists who have endured serpentine detours, earthshaking noise and traffic delays for more than a year.

A mistake of about five inches forced a private contractor to tear down a ramp it was building on Seattle’s South Spokane Street Viaduct, just as progress was becoming visible to aggravated motorists who have endured serpentine detours, earthshaking noise and traffic delays for more than a year.

The ramp on First Avenue South was rising from the roadbed toward the viaduct when a worker noticed last week that the freshly poured concrete footing wasn’t lining up the way it was supposed to.

After considering its options, PCL Construction of Bellevue opted to tear down 160 feet of concrete and start over.

“It’s our mistake, and we own those things,” said Anthony Sturgess, PCL operations manager, who estimated the error will cost the company between $20,000 and $25,000. A surveying error created the misalignment, but the company hadn’t identified how the error occurred, Sturgess said.

The tangle of rebar and concrete was expected to be trucked away Friday.

The First Avenue South ramp is part of a series of improvements designed to improve traffic flows on and around the Spokane Street Viaduct. When completed, the 300-foot, two-way ramp will funnel cars to and from the viaduct’s westbound lanes.

Despite the mistake, PCL still expects to finish the ramp by fall, he said.

That’s good news for motorists and nearby businesses.

“It pains me just to have to watch this all happening again,” said Mark Hergert, a railroad-track modeler/programmer who has a front-row view of the action from his workplace at Nortrak. “It was so nice to see progress being made.”

The Seattle Department of Transportation is overseeing the project. Spokeswoman Mary Beth Turner said the mistake resulted in a five-inch discrepancy. “They built it straight when it was supposed to be curved. People aren’t always perfect. Mistakes happen.”

Susan Kelleher: 206-464-2508 or skelleher@seattletimes.com