A very large elephant in the room is about to be acknowledged. That would be state House Speaker Frank Chopp's long-concealed pet scheme for the Alaskan Way Viaduct, which becomes public today, Sept. 25, at a meeting of the project's Stakeholder Advisory Committee (4-7:30 p.m. in the Bertha Landes Room of Seattle City Hall). Chopp has been passionately advocating this plan for the past year but not allowing public disclosure or debate. (Unless you're an insider, you're seeing it here first.) The plan is wildly unpopular among politicos who know of it in Seattle. Chopp is wildly powerful in Olympia. Collision time.

After a year of semi-public meetings among planners, the leading contenders for a Viaduct solution had been:

• A surface-transit solution (no highway replacing the Viaduct, but a slow boulevard and lots of traffic diverted through downtown Seattle).
• A bored tunnel under the city, not along the waterfront.
• A low-cost tunnel/trench along the waterfront with a surface boulevard on top.

The Choppway is very different from these. He would build a mega-structure where the Viaduct now stands, just as high and almost twice as wide. The two ground floors would be developed as commercial space all along the structure, except for portals at street crossings. Next level would be an enclosed highway, three lanes in each direction (maybe one lane each way for buses), with vent openings at each cross street cutting under the highway. Atop would be a park with splendid views of Elliott Bay, 90 feet wide and extending more than a mile from the Pike Place Market to South King Street. Lastly, surface traffic would be routed to the east of this megaduct and along Western Avenue, so the (rather narrow) promenade on the waterfront, alongside the docks, would be traffic- and (almost) noise-free.

Chopp is a man possessed. He put the idea down on a napkin in 2001, around the time that the Nisqually Earthquake rattled the now-55-year-old Viaduct, putting it on a list of must-do projects. He's shopped the idea around tirelessly and considerably improved it. One adopted idea, not quite solid, is to take two of the four lanes and dedicate them to Metro Transit bus rapid transit lanes (with stations at Pike Place Market and Pioneer Square). Another idea is adding a large park on Pier 48 just south of the Colman Dock ferry terminal, and maybe also a park in front of the Seattle Aquarium. Chopp's architects have improved the facades and cross-street portals; one nice touch is adding arcades in the retail portions, providing more rain protection.

In effect, the Choppway moves downtown Seattle one block westward and gives the downtown a long front yard. Chopp loves the way it saves the view from the current Viaduct, giving it to all sorts of people who can savor it while strolling rather than shooting glances from a speeding car. Hearing him sermonize about it, one would think it's going to be his legacy.

One big problem is that nearly every interest is lined up against it, including downtown Seattle interests, the design community, the anti-auto, anti-freeway crowd, and people who just want to get a solution, not another donnybrook. Naturally, these people have found it almost impossible to express their real views to Chopp, who just happens to be the most powerful politician in the state, with a personal machine in the House that will do his bidding.

All of which means we are probably heading for a 47-car pileup. Here's how that happens. Following the disastrous election last year, in which voters turned down both a new viaduct and a tunnel, Gov. Chris Gregoire headed for the foxhole, putting in place a year-long study among stakeholders, advocates for various solutions, and the transportation departments of the city, King county, and the state. (Very good process, one gathers.) This process in a month or two provides an analysis of the costs and benefits and problems with all eight solutions that have survived (including Chopp's, called "Scenario E"). Mayor Greg Nickels, county Executive Ron Sims, and the governor (who, of course, might be Dino Rossi, who favors a bored tunnel) then pick the winner, if they can. City and county councils weigh in (probably sheltering behind the mayor and the executive). Then the Legislature. Uh-oh. That's the point where Chopp, if he wishes, easily has the power to veto any plan that is not his pride and joy. Like I said, collision time.

Accordingly, Chopp has been driving the consensus-desperate folks crazy. Is he just putting his idea forth and hoping for fair treatment? Might he go along with the process, even if his idea loses? (I asked Chopp about this, and his way of saying no was to wonder if the other losers would concede and to remind everyone that "the Legislature has to weigh in.") Is he open to compromise? Or is it, as most fear, "My highway or no way!"

I've had a couple long sessions with Chopp, hearing his passionate commitment to his idea. He recalls growing up in Bremerton, looking out his bedroom window at the Olympics, and wanting all citizens to have that inspiring view. He talks about an example in Paris, the Promenade Plantee, 4.5 kilometers of the "Green Stream" atop a defunct railway viaduct, or the Highline in New York City, a 22-block park projects on top of an abandoned rail deck. Chopp has hired an architect, Kevin Peterson, to refine his ideas. He's hiring public relations counsel. He's got some business leaders to make his case with leading politicians. He's also famously stubborn and shows no signs of conceding.

But he's very late in the game. Most of the town's politicians and business leaders have sworn blood oaths against building another Viaduct, which many consider a great folly of the freeway-mad 1950s. Developers are intent on open views and getting rid of the Viaduct's noise and fumes, so they can build expensive waterfront condos down there. It's become a lie-down-in-front-of-bulldozers kind of issue. And Chopp's gruff, secretive ways have not made him a lot of friends in Seattle (though many fear him and do deals with him), especially when he swatted away the first Viaduct solution, a tunnel, and didn't lift a finger to save the SuperSonics. In return, Chopp has only been goaded onward by all the put-downs by Seattle's design community, which literally would not give him a hearing.

It's also been hard to perceive what he really had in mind, particularly as the plan evolved. (Every time someone criticises his plan, he says that he's already changed that feature, but is not ready to show it.) Where the plans have ended up, however, is intriguing. That long elevated promenade really would be a signature feature of Seattle, bound to be popular as such belvederes in European cities or New York's Riverside or in Quebec City. It would doubtless stimulate development, particularly on the north end of the downtown waterfront, where the highway structure is tucked along a hillside. The autoless promenade below would be narrow (40 feet) but quiet. And if the commercial structures really did work, they would bring the missing ingredient to the waterfront — people, year-round.