SPECIAL TUNNEL ISSUE

Our Own Big Dig?
No. But, It's Also Not That Simple


Boston Big Dig – Before and After


It might seem like there couldn't be anything more to add to the avalanche of media reports concerning the new plan to replace the Alaskan Way Viaduct with a deep bore tunnel. But, the eight-year saga that dates back to the 2001 Nisqually quake has just taken another turn in what will prove to be a very long road. Below you'll find some things to keep in mind as we look ahead to the next few chapters.

Big Dig? Nope
Some deep bore critics say taxpayers are being set up for a fiasco like the Big Dig in Boston. This concern is understandable, but mostly misplaced. The real Big Dig was a far larger, more complex project that combined a huge cut-and-cover ditch with an underground tube, an additional tunnel and a huge surface road project that rerouted a 3.5-mile stretch of interstate freeway that once carried nearly 200,000 cars per day through the heart of Boston. By the time it was all over, and debt costs were included, it was estimated that the final price tag will eventually reach a walloping $22 billion.

The two-mile Seattle tunnel is presently envisioned as a single bore structure with a radius of 54 feet housing four lanes carrying 80,000 to 85,000 cars each day, with estimated tunnel construction costs of $1.2 to $2.2 billion with related costs bringing the total to something more than $4 billion.

Now, this isn't to say our tunnel might not turn out to be a fiasco, but if it does, it won't be the magnitude of the Boston Big Dig – it would be a fiasco all our own based on local circumstances.

Then again only 1% of the required engineering has been performed, so there's a 99% chance this could all turn out far differently than it looks today.

Deep Bore Estimate Gap
According to the rumor mill, a Ballard spur of the deep bore tunnel could cost as "little" as $200 to $300 million to build, not the $900 million quoted by transportation planners.

These figures or ones like them will probably become more public as the tunnel study moves forward because the present plan is for the north end of the tunnel to stop somewhere east of the KING TV station in south Lake Union, with no underground connection to northwest Seattle. That's a big concern because about 35,000 cars from northwest Seattle presently use the Alaskan Way Viaduct every day for north-south access through the downtown, and most of them reach the viaduct and SR 99 via the ramps at Elliott and Western. It's not really known how these motorists would go about gaining access to the north entrance to the tunnel.

Why the big difference in cost estimates for the Ballard spur? Hopefully, it could mean it might be more feasible than the government planners think to build the Ballard spur. Or, it might wind up that the discrepancy is due to something that might be called the Deep Bore Estimate Gap.

As we are about to learn, the world of deep bore tunneling is an intriguing place occupied by enormous boring machines that are capable of amazing feats while operating hundreds of feet below the surface. But, while the boring machines are huge, the tunneling world is very, very small, with very few actual tunnel builders.

This makes government transportation planners very leery of tunnel costs estimates from the private sector because of the potential self-interest of those who might be talking up the relative low costs of deep bore tunnels. For this reason, we will no doubt continue to hear that there are major differences between the cost estimates.

In a KIRO radio interview yesterday, Governor Gregoire said the state is adding 25% to its tunnel cost estimates as a hedge against overruns.

If it turns out the extra 25% isn't needed, that would work out to $300 million to $550 million, and, who knows? That might be enough to build a tunnel extension to Ballard.

Other Tunnels
The state's estimate works out roughly to $600 million to $1.2 billion per mile. Just for entertainment purposes, here's how the numbers compare with other tunnel projects described on the website of the pro-tunnel Cascadia Center think tank in Seattle.

Port of Miami Tunnel (proposed); diameter 36 feet; twin bore; total tunnel length 1.5 miles; $1 billion total cost; $677 million per mile.

Airport Link, Brisbane, Australia; complete date 2012; diameter 41 feet; twin bore; total tunnel length 6.5 miles; reported cost $2.2 billion; cost per miles $338 million.

Fourth Tube of Elbe; completed 2002; diameter 47 feet; single bore; length 2.6 miles; reported cost $775 million; cost per miles $303 million.

I-710 freeway, Los Angeles; proposed; diameter 50 feet; triple bore;
4.1 mile alignment length; total tunnel length 12.4 miles; reported cost $3.6 billion; $290 million per mile.

Beacon Hill Sound Transit Tunnel, Seattle; diameter 21 feet; twin bore; alignment length 0.8 miles; 1.6 miles total length; reported cost $280 million; $172 million per mile.

Nanjing, China; to be completed 2013, 49 foot diameter; twin bore; alignment length 1.9 miles; total length 3.7 miles; reported cost $245 million; $66 million per mile.

As we said, this was an entertainment exercise. We came up with slightly different per-mile costs when we did the math on our own and we're not sure what all is included in the costs.

Actual costs here could be dramatically impacted by related costs for changes to Mercer Street and other roads near the northern portal. Same goes for roads near the portal to the south near the sports stadiums.

Stay tuned. There's a lot more to come.

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Link Light Rail SODO Open House January 22
Sound Transit's Link light rail trains are on the way! SDOT needs your input on proposed Link light rail neighborhood parking plans.

Attend the SODO Open House on Thursday, January 22nd - Mezza Cafe, Starbucks Corporate Building, Floor 3, 2401 S Utah St/S Lander St from 10 am - 12 pm. Light refreshments will be available.

More information can be found at:
http://www.seattle.gov/transportation/parking/lightrailparking.htm

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