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So the peak number of cars to surface streets after the Viaduct is closed will be somewhat less than 10,000.To get a finer-grained look at where the traffic problems might be most severe, you can break down the trips on the former viaduct corridor into zones--Belltown, Downtown Core, Pioneer Square/Stadium, etc.--and look at the actual increase in travel demand in each zone.
If that's possible, then the tunnel alone would be meet the post-Viaduct demand.) And then there's Third Ave., which is currently closed to cars during rush hour.Now, without a Viaduct, some of those peak-hour trips will take quite a bit longer -- so people will shift their trips to other times of day, other modes, or forego them altogether.Based on published estimates of how much an increase in travel time decreases travel demand, it looks like demand for car trips may drop from 12,000 trips to 10,000 during the afternoon peak hour.So the thorniest problem that traffic planners will have to face will be accomodating rush hour trips on the street grid and I-5, during the busiest part of the day. And what are the options for dealing with the added load?Earlier this week, the helpful and responsive folks at the Seattle Department of Transportation sent me some data that may help shed some light. (Feel free to skip the next few paragraphs if you're not a traffic geek.) Each year, the city collects data on traffic flows on the major arterials around Seattle, including the Viaduct and its on- and off-ramps.So getting 11,000 people to shift from driving alone to the bus would boost rush-hour transit ridership by a little more than a third -- tough, maybe, but not inconceivable.
And in theory, at least, there's ample capacity to handle that many trips in the bus tunnel, which is now closed for service.
And by 2032, today's population of roughly 825,000 will grow to the milestone of a million residents.
San Francisco will have grown in population by 35 percent between 20—"the fastest 30-year rate of increase in nearly a century." "'The Bay Area job creation engine is the envy of the entire world,' said Gabriel Metcalf, executive director of SPUR, the region's most active urbanist think tank.
Over the course of a rush hour that lasts at least an hour and a half, that means that transportation officials will have to worry about accomodating the demand for some 11,000 addtional trips in the busiest part of downtown, during the busiest part of the day. Still, even with those improvements, the demand for 11,000 extra trips could really jam up the afternoon rush hour.
Even if people eventually adjust to the congestion -- by changing schedules or jobs, or switching to transit -- the early months could be brutal.
Sure, a trip along the Viaduct-less corridor would take a little longer than it does now; but the steet grid could easily handle the load.