Seattle’s viaduct to head underground

SEATTLE — So it’s official.

The creaky, congested Alaskan Way Viaduct, which carries State Route 99 along the downtown waterfront while providing bird’s-eye views of Elliott Bay, will be replaced by a tunnel.

The decision, spurred by damage caused and revealed by the 2001 Nisqually earthquake, was announced Monday by Mayor Greg Nickels and state and federal transportation officials.

The idea is that a $4.1 billion, 5,300-foot-long tunnel — built over seven or eight years — will allow removal of the viaduct’s crumbling concrete pillars, which wall off the waterfront at the south end of downtown.

Removing the viaduct will free up space, cut down noise and open up access to waterfront attractions such as the ferry terminal, port offices, restaurants, the Seattle Aquarium and souvenir shops, making it “more accessible and more enjoyable for all,” the mayor’s office said in a news release.

The tricky part will be hooking up to the Battery Street tunnel that now marks the end of the 2.2-mile viaduct and, like much of the central and north downtown area, is perched on bluffs 40 or 50 feet above the waterfront.

The city is proposing that after about a mile in the tunnel, cars and trucks would emerge into a lidded roadway at ground level, said Grace Crunican, Seattle’s director of transportation. The roadway then would begin rising along the bluff to connect with the existing tunnel north of the Pike Place Market.

The grade will not exceed 7 percent — about the same as the Magnolia Street Bridge and the West Seattle Freeway, Crunican said.

About 5,000 of the 100,000 vehicles that use the viaduct daily are trucks, she said, “and if you go beyond 7 percent you’re stretching it. Trucks wouldn’t be able to handle the grade.”

The lid will be planted with low-profile vegetation and provide a sort of extension to Victor Steinbrueck Park, just north of the market, with a sidewalk for folks who want to walk to the waterfront on top of the lidded six-lane road.

“You would have a walkway park experience,” Crunican said. “We’re not trying to block the view of Elliott Bay.”

The tunnel will be equipped with vents and escape routes and “the most modern fire equipment,” Crunican said.

Vehicles inside would reach open air at about Virginia Street, a couple blocks beyond the market.

“So you get a good taste of the view there” before entering the Battery Street tunnel,” she said.

The tunnel also will incorporate portions of the seawall, which also needs replacement.

The city has dutifully repaired breaches in the seawall since it was built, in stages, between 1915 and 1936. But where there was air and water, there were gribbles — microscopic wood-eating sea lice that have damaged support timbers.

The city hopes to secure $1 billion in Federal Highway Administration funds, plus $100 million from the Army Corps of Engineers for the 1,700-foot stretch of standalone seawall that is not part of the tunnel.

Also contributing money will be the city, the state, the Puget Sound Regional Council, the Port of Seattle and utilities.