A fledgling citizens group yesterday unveiled another alternative for replacing Seattle's fragile, aging Alaskan Way Viaduct:

Don't.

The viaduct should be torn down, the People's Waterfront Coalition said, but building a replacement would be too expensive and disruptive.

Instead, it proposed a package of smaller projects to keep traffic moving through downtown without the viaduct. They include reconfiguring Interstate 5, improving downtown arterials and signal timing, expanding transit, and adopting tolls and other strategies to discourage driving.

"It's about using existing resources more efficiently," said Cary Moon, a Seattle landscape and urban designer who is one of the coalition's leaders.

The group also called for:

• Restoring the downtown shoreline to a more natural condition, with beaches, parks, breakwater islands, paths, an amphitheater and a marina.

• Dense residential and commercial development on some central waterfront blocks now occupied by the viaduct.

• Rebuilding Alaskan Way as a four-lane city street connected to the rest of the downtown grid.

Moon and Grant Cogswell, another coalition leader who is a monorail activist and former City Council candidate, said they may present their plan to city voters as an initiative.

As a first step, however, they called on the state Department of Transportation (DOT) to subject the coalition's proposal to detailed environmental study.

The agency already is studying five viaduct-replacement alternatives and has scheduled hearings on them later this month.

The 51-year-old viaduct was built along the downtown waterfront on soils that could liquefy in an earthquake. Plans for replacing the two-level elevated thoroughfare took on added urgency after it was damaged in the 2001 Nisqually earthquake.

The replacement options DOT has singled out for study range from a six-lane surface boulevard, with an estimated price tag of $2.5 billion to $2.8 billion, to a waterfront tunnel that could cost between $3.8 billion and $4.1 billion.

Coalition leaders acknowledged the tunnel option also would help reconnect the waterfront with downtown. The problem is the price tag, Cogswell said: "We don't want to put a whole generation's transportation money into a highway on the shore."

Cost overruns for such "megaprojects" are commonplace, he added, and construction of any option would disrupt the waterfront for years.

State DOT spokeswoman Linda Mullen said the department decided not to study the option of tearing the viaduct down without replacing it because "we just thought that you've got to put the traffic someplace."

The viaduct and Alaskan Way carry 110,000 vehicles on a typical weekday. By 2030, Mullen said, that will increase to 130,000.

She questioned whether the changes that the coalition has proposed elsewhere would accommodate or eliminate those volumes.

While the coalition's vision for the waterfront "is fabulous," Mullen said, "I'm not sure how feasible it is in terms of handling the traffic."

Marianne Bichsel, spokeswoman for Seattle Mayor Greg Nickels, agreed. "The mayor says they're half-right — we do need to open up the waterfront," she said. Nickels has favored the tunnel option.

"But the mayor believes we need to replace the (viaduct's) capacity," Bichsel added.

Eric Pryne: 206-464-2231 or epryne@seattletimes.com