Truth Needle: Mayor's tunnel claim half true

The claim: Seattle Mayor Mike McGinn said last week on a radio appearance that the state's data show the planned Highway 99 tolled tunnel would cause the worst downtown congestion of all options to replace the 58-year-old Alaskan Way Viaduct.

What we found: half true

McGinn, in an interview with KUOW radio host Steve Scher on April 11, said: "Tunnel plus tolls causes the most traffic congestion of any option, including any type of transit-surface option." He went on to name a state report from which he drew that conclusion.

We took a look at the same numbers, and the state does predict its tunnel plan would mean more car traffic in the area, which the anti-tunnel McGinn points to as more congestion. But the state's research also says drivers would reach their destinations sooner compared with the surface-transit option McGinn favors. Because of that, we find McGinn's statement half true.

The state — like many individual drivers — defines congestion as how slowly a vehicle moves, not as how many cars are on the road. Think of the state's multicolored online highway maps that show congestion. Black lines don't mean that's where the most cars are, just that those cars aren't moving much.

Ron Paananen, the state Highway 99 administrator, said the mayor's office is "cherry picking" from a yet-unpublished technical report, by ignoring travel time. For instance, a trip from West Seattle to the financial district might take 25 minutes in the state plan, or 37 minutes under surface transit, the state research says.

"The travel times increase quite a bit under the surface-transit scenario compared to a tunnel, anywhere from a couple minutes' difference, to 15 minutes," Paananen said.

McGinn explained in a later interview that his comments were based on a spreadsheet by a city transportation planner who distilled figures from an upcoming Transportation Discipline Report, to be published as part of the tunnel's final environmental-impact statement this summer.

The spreadsheet says that, based on modeling of the central city, a tolled tunnel in 2030 would produce 2 percent more total hours of daily vehicle delay compared with a surface option.

An elevated structure or a cut-and-cover tunnel, neither of which would have a toll, would fare better on this criterion, although most differences would fall well within a likely margin of error.

One problem with the mayor's interpretation is that the state's "vehicle hours of delay" numbers don't divide by the total number of cars, or describe specific street conditions.

The state's draft research says vehicle hours of delay is "often used as an indicator of overall traffic congestion." However, more cars don't necessarily mean drivers would be stuck longer, because the state Department of Transportation (DOT) is providing road capacity, Paananen said.

In addition to a tunnel, the state would add a bridge linking Belltown to Alaskan Way on the waterfront. Farther south, the street would expand to six lanes, from the ferry terminal to a new stadium interchange.

"They can say they have more capacity. Doesn't it mean just that there are more cars out there?" replied McGinn, who favors people driving less to reduce carbon pollution.

The surface option compared by DOT wasn't a quiet four-lane road, but an unpopular six-lane version that would turn Western Avenue into a three-lane northbound throughway, alongside three lanes southbound on the waterfront. In the 2009 mayoral campaign, McGinn objected to a six-lane stretch farther south, from the ferries to the stadiums.

On the other hand, it might be possible to devise a bolder menu of transit and land-use policies than DOT has considered to move people through downtown. McGinn has suggested a west-side light-rail line.

Meanwhile, the mayor also supports the Protect Seattle Now referendum, which seeks to repeal tunnel agreements between the City Council and the DOT.

Despite flaws in McGinn's sound bite, his argument is partly right, to the extent that state environmental studies do acknowledge major problems with toll diversion.

At a possible range from $1 during off-peak traffic hours to $4 peak, tolls would shift 40,000 to 45,000 daily trips to other roads and Interstate 5 — half the drivers who would use a free tunnel.

Barring some solution, governments risk dumping traffic onto historic Pioneer Square, or along the promised parklike bay shore.

"That's the point I've been trying to raise," McGinn said.

He added that, even as Gov. Chris Gregoire and other tunnel backers argue that a surface-transit-interstate option should be disqualified because of traffic diversion, "tunnel plus tolls is equally flawed, or worse."

One trend jumps from the city's spreadsheet. Overall hours of car delays in central Seattle would be 16 percent greater with tolls than without tolls.

Paananen admits the difference "shows the challenge we have."

The city soon will issue a report by consultant Nelson Nygaard about ways to protect the core from toll diversion.

"Frankly, it is very difficult to mitigate without significant investments in transit," McGinn said.

The viaduct now is scheduled to be torn down in 2016.

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