Tunnel would mean more traffic on waterfront

Even if the state replaces the Alaskan Way Viaduct with a four-lane tunnel, life on the street would get busier.

The $2 billion, 1.7-mile Highway 99 tunnel creates a dilemma: how to move traffic without ramps leading to downtown and Interbay — which about half the viaduct drivers use today. Not only would those commuters need new routes, but thousands of other drivers likely would avoid tunnel tolls by shifting to downtown streets.

The average person might be surprised at how much roadway is proposed to supplement the tunnel.

To lower the odds of gridlock, the waterfront route on Alaskan Way would be enlarged, to six lanes from Sodo to the ferry terminal and four lanes north to Belltown. The new boulevard and interchanges, which would push the overall cost to $3.1 billion, would soak up most of about 34,500 cars and freight trucks that now take the Elliott and Western avenue ramps.

Alaskan Way wouldn't be just a tourist street anymore.

Right now, traffic is light, except for cruise-ship arrivals, warm summer weekends and game days at the stadiums.

But if the new boulevard were so convenient that cars flock to it, it could wreck the whole point of tunneling, which is to replace the viaduct with a quieter, parklike, roomier shoreline.

No more ramps

On a typical weekday morning, the six-lane viaduct is a workhorse, carrying not only commuters heading to downtown and Interbay, but drivers passing through downtown. Cars line up a half-mile to exit northbound at Western Avenue in the morning, and to enter southbound from Elliott Avenue in the afternoon. Midtown ramps at Seneca and Columbia streets feed directly into the financial district.

But those ramps would disappear in 2016, if the highway is moved underground.

Ron Paananen, Highway 99 program director, predicts drivers would split about "half and half" between those using the boulevard to reach Ballard and Interbay, and those who use the tunnel and then head west to Ballard.

Commuters heading downtown from the south would have to exit Highway 99 in Sodo, then drive on a rebuilt street grid.

Overall, the tunnel is expected to carry at least one-third fewer vehicles than the viaduct.

And there's the balancing act of trying to set tolls high enough to bring in $400 million the state is counting on, yet low enough that drivers use the tunnel instead of clogging surface roads.

"It's in everyone's interest to have those trips be in the tunnel that want to be in the tunnel," said Mark Bandy, state traffic engineer.

The tunnel team will publish fresh data in a month through a supplemental draft environmental impact statement — the same one Seattle Councilmember Richard Conlin signed in an attempt to outmaneuver anti-tunnel Mayor Mike McGinn. The state wouldn't provide a copy, but earlier documents and interviews show some of the strategies.

Busier waterfront

A huge Sodo interchange south of the tunnel near the stadiums would link drivers to six lanes, as well as to the Interstate 5/I-90 junction at Edgar Martinez Drive. About 20,000 daily car trips would be added to nearby streets.

To the north, Elliott and Western avenues would connect to the new boulevard via a mini-viaduct over the BNSF Railway tracks below Victor Steinbrueck Park.

The state agreed to boost road capacity so the plan would work for Seattle businesses, said Dave Gering, executive director of the Manufacturing Industrial Council.

Truck access 10 years from now might be better than today, said Dave Freiboth, executive secretary of the M.L. King County Labor Council. Instead of one onramp to the southbound viaduct, drivers could reach the surface boulevard at two points, or enter the tunnel's north portal at a new Mercer Street interchange.

"They will have more options to work with," he said.

A surface boulevard might attract 35,000 vehicle trips a day, a state toll study predicts — about three times the present amount. Such numbers push the limits of what's acceptable to still allow a pleasant waterfront. Gehl Architects, in a 2008 urban-design report for the city, defined the 25,000-trip level as a "poor street."

The boulevard would operate at relatively quiet 30 mph speeds, and there would be 80 feet of open space to the water to help move bicyclists and pedestrians. "This is a very wide corridor," Paananen said. "There are opportunities."

Buses, bikes, on foot

What about those who don't drive?

Buses already serve 26,000 riders on Highway 99 heading in and out of downtown, and the state expects that number to grow.

A transit exit lane is planned in Sodo for buses arriving from West Seattle, Tukwila and Burien. Bus routes from there to downtown are unclear, but planners are working on an east-west corridor, perhaps Main Street, to reach the Third Avenue busway. To the north, transit bypass lanes are planned from Aurora Avenue into Belltown and Third Avenue.

No proposal exists for Highway 99 buses between Sodo and South Lake Union. James Kelly, co-founder of the new pro-tunnel group Enough, said transit should operate in the tunnel.

The pedestrian group Feet First and operators of Bill Spiedel's Underground Tour have worried about seemingly vague ideas for managing increased traffic through historic Pioneer Square. Tour CEO Sunny Spiedel urges the city to demand answers before the state signs its construction contracts.

"Done poorly," she said, "this could ruin either our fragile neighborhood or our connection to the new waterfront."

Ample off-street bicycle trails appear in the Sodo design, but the plan from Pioneer Square to the Olympic Sculpture Park at the north end of Belltown remains a mystery. Some bike lanes, or a raised "cycle track," would be part of the boulevard, said Eric Tweit, a Seattle transportation project manager.

Off-street trails are to be decided. Seattle has hired design firm James Corner Field Operations to consider such things, as it designs nine acres of promenade between the boulevard and Puget Sound.

David Hiller, advocacy director for the Cascade Bicycle Club, said the state traffic predictions tend to assume long-term growth when, in fact, overall driving in Seattle was flat through the 2000s.

Taking a toll

Transportation forecasting is notoriously fallible.

"It's possible to be really far off, as much as 20 percent," said Mark Hallenbeck, director of the Washington State Transportation Center. He said officials in 1963, underestimating how fast the Eastside would grow, didn't believe the deck of Highway 520 would be busy enough to need shoulders.

But Highway 99 already is a developed area, so other factors matter more to Hallenbeck: What if parking costs change dramatically? What if the city elects a pro-driving mayor? Will economic growth return this decade, bringing more jobs and traffic into Sodo?

Most important of all are the toll rates, he says.

A free tunnel would attract 94,000 as of 2030, but tolls would cut demand to 62,000 vehicles a day through the tunnel while diverting thousands to the boulevard, reports say. Paananen said last week that opening-year tunnel use would be less, at 47,000, assuming tolls that vary from $1 to $4 depending on time of day. Growth gradually would increase tunnel traffic. But Paananen also said he believes state figures are conservatively high.

In his campaign last year, McGinn conjectured about a death spiral, where tolls discourage so many drivers that the state can't raise money, so rates are jacked up higher, until there's not enough demand to justify a tunnel.

Hallenbeck said the toll- study numbers appear credible, but we don't really know how politics eventually will affect them.

"And what else gets tolled?" If drivers had to pay to use I-5, or if a London-style boundary were set to toll all car routes entering Seattle, that would hugely affect Highway 99.

"If you toll everybody, you limit the diversion," Hallenbeck said. "They don't do the rat runs through the city."

Mike Lindblom: 206-515-5631 or mlindblom@seattletimes.com