Tuesday 20 September 2011

Seattle's toll tunnel to replace untolled viaduct (UPDATED)

Route of the tunnel
Those unfamiliar with the story of the Alaskan Way Viaduct should read this. In summary, this viaduct is a six-lane part of Washington State Route 99 running along the Seattle waterfront. It was damaged in the 2001 Nisqually Earthquake and faced either needing to be repaired or replaced. Replacement was to cost up to US$3.5 billion, but as the viaduct runs along the waterfront of the city, it was seen as a chance to do something different (don’t ask why it wasn’t insured like any privately owned infrastructure). The options narrowed down to a bored tunnel or a surface street option.

Environmentalists argued, remarkably, that it would be better to demolish the viaduct and not replace it, so that traffic would be pushing through surface streets. The presumption is that the resulting severe congestion would simply deter many from driving and so have a positive impact – except of course for those who DO need to use the route (even buses and trucks), and anyone walking, cycling, working or living along the surface route. A clear case of local environmental gains being overridden by those wanting to wage a war against road traffic.  Indeed they even argued that the tolled tunnel would be no better on the streets that just demolishing the viaduct and routing traffic through town.

SR 99 tunnel, two lanes stacked
A postal referendum on the options came out in favour of the tunnel, which is an innovative stacked tube design as seen here. 

So the state has signed a construction contract to break ground on a $2 billion, 1.7-mile tunnel from Sodo to South Lake Union in September, to replace the Viaduct by 2016.
The problem with the tunnel is that as it will be tolled (and be four lanes whilst the viaduct is six lanes), and the environmental-impact statement claims that some 40,000 to 45,000 cars a day as drivers dodge a cost of anywhere from $1 overnight to $5 in the southbound afternoon peak. Yes, the tolled tunnel would have peak congestion pricing to manage demand. The state predicts that by 2030, about 57,000 cars would pass through the tunnel each day under the current proposed tolling plan, compared with 93,000 if the tunnel wasn't tolled at all. The city may gain a waterfront, but will also gain more downtown traffic. The question may yet be raised as to whether downtown congestion pricing might be a useful strategy to limit this, indeed the environmentalists might be better focused on that, now that an effective bypass is to be built.  

Traffic on the highway has been largely static in the last decade, hovering around 110,000 daily trips near Seneca Street, or 63,000 through the Battery Street Tunnel.
According to the Seattle Times, Highway 99 project Administrator Ron Paananen claims that the tunnel project, with a widened Alaskan Way south of the ferry terminal “preserves similar overall capacity to the current viaduct”. The FHWA has also signed off on the option.

Seattle isn’t unfamiliar with tolls, with the following existing projects:
- Tacoma Narrows Bridge;

Big inner city toll tunnels are a modern solution to getting major traffic to bypass built up areas. They are not cheap, but they are permanent and make an enormous difference to traffic flows and the local environment. I wish Seattle the very best with this project and hope the traffic management and design for the surface routes is good enough to balance the needs for traffic and the desire to unlock the value of the land along the waterfront that will be freed up by removal of the viaduct.

Tolling will be electronic free flow and the pricing will need to be attractive enough to appeal to a majority of the existing users of the viaduct.

Full details on the project, including a cost breakdown are here.

UPDATE:  Useful details provided in the comments below, a key point being that much of the current traffic on the viaduct is entering and exiting the downtown.  The tunnel will be simply a bypass, so in fact it will be providing tolled capacity only for those bypassing, the existing streets will have to manage (with some widening work), begging the obvious question as to whether congestion pricing might be helpful?


  1. Missed some small details that make this project and the proposed tolls somewhat unique:

    1) the majority of the existing 6-lane viaduct traffic is exiting or entering the highway in the area. The tunnel replacement will have no exits in the project area, and will purely be a bypass route.

    2) A new 6 lane surface couplet (a pair of 3 lane 1-way streets) is going to be installed for local access near the viaduct's current route, to replace all of the existing downtown exits. It will be untolled.

    3) There are several untolled alternative routes, including the aforementioned surface couplet as well as a parallel interstate highway less than a mile to the east.

    4) A statewide initiative headed for the ballot this November (I-1125) will effectively ban all forms of variable tolling statewide if passed (among other things). The campaign is well funded by local antitax activists, and it is likely to pass.

    The pricing will need to be very "attractive" to attract users, given the alternative routes available and the small amount of traffic that currently uses SR-99 as a bypass. But the financing for the project does not look feasible without a high peak-hour toll. And if (when) I-1125 passes, the tolling picture gets much worse.

    You also somewhat misrepresent the "environmentalist" alternative, which actually was much more detailed than just "people will adjust". It involved many capacity-increasing changes to the downtown street grid and parallel interstate, in addition to bulked up transit, but it's a dead proposal that's outside of the scope of this blog so I won't go into it in detail. Most Seattle residents dismissed it as easily as you did - it had no backers with any political clout and didn't have an effective campaign advocating for it.

  2. Thanks for that, yes that is all very helpful detail. I have been following Initiative 1125 and commented on it, it looks like a disaster for this project.

    It is a very challenging project, and in fact is more "environmental" than many may think, as it will mean quite some adjusting given the usage you mentioned in point 1.