I wouldn’t call it momentum, exactly, but there seems to have been a bit of movement on the idea of replacing Seattle’s Alaskan Way Viaduct with a surface boulevard—a modestly-priced alternative to an aerial rebuild or tunnel. Now, just to be clear, I’m still not convinced that this is an ideal solution. Transportation is complicated, and while other US cities that have removed downtown highways (San Francisco, Milwaukee, and Portland) have never suffered the gridlock that skeptics predicted, the unique layout of Seattle’s traffic corridors, industrial areas, and job centers might mean that losing the Viaduct’s capacity would create nightmare rush hours for people working (and living) downtown.

Except there’s this:  the current plans for the tunnel and aerial rebuild already assume that the city can make do without the Viaduct for three to four years.  That’s how long it will take between the moment the existing structure is closed for demolition, and the new one is open for traffic.

Now, I’ve heard plenty of people argue that traffic will come to a standstill if the Viaduct is replaced by a surface boulevard.  But I’ve never heard anyone from the city or state admit that their prefered options will do the exact same thing, for at least three years.

So either: a) transportation officials aren’t being up-front about this—and the replacement options have a hidden downside that nobody’s talking about publicly; or b) they don’t think it’s really all that much of a problem, and that they’ll cobble together some combination of transit incentives and surface street improvements that will keep traffic flowing.  And if it’s the latter, then, goodness gracious, if it can work for 3 years, then why not 10, or 20, or longer?

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  • More to the point, it seems to me that there’s pretty good reason to believe that downtown traffic won’t have to come to a halt if the Viaduct is closed.

    The official figures say that the Viaduct carries 105,000 trips per day.  But during much of the day the Viaduct is lightly travelled, and there’s usually extra capacity on surface streets and I-5.

    The real problems might come during rush hour, when just about every traffic conduit in downtown is full.  But in reality, not that much traffic actually travels on the Viaduct during rush hour.  With only 2 lanes, the Battery Street Tunnel carries at most 10,000 vehicles into downtown during a typical morning rush hour, and 10,000 northwards at the end of the day.  (This is assuming 2.5 hours of rush hour, and a generous 2,000 cars per lane per hour.)  So that means—from the North anyway—that the transportation system needs to deal with about 10,000 round trips that would no longer be able to go on the Viaduct.  (I haven’t thought things through, but I bet it’s a similar number of round trips from the south.)

    That’s still a lot of trips, but it seems a lot more manageable than the official figure of 105,000.  And there are lots of options to keep people moving.  A new boulevard could handle some of the car and truck trips. Sound Transit may take some pressure off I-5 and other surface streets once it opens.  Improved bus service—more buses combined with priority timing for buses at traffic lights—could carry many of the commuters.  Tweaks to the street grid could help keep traffic flowing a bit better.  Some people will simply opt to take their trips at different times of the day, or even forego them.  (Even during rush hour, only a minority of trips are direct trips between work and home.)

    Those are just the conventional options.  One unconventional solution—or unconventional in the US at any rate—would be to try what Stockholm and London have already done:  charged drivers to enter downtown. Both congestion pricing schemes have been more successful than critics might have predicted:  congestion has gone down enough that many commuters believe the tradeoff is worth it.

    But the thing to remember is this: unless the city decides to leave the Viaduct as it is (or to retrofit it as some have suggested) this isn’t really an optional exercise. The city is going to have to do some combination of these things, and people are going to have to adjust.

    The only question, then, is whether the residents of greater Seattle should spend a few extra billion dollars to fix a problem they’ve already solved.