In this week's In the Hall, I'll be writing about the prospects for Frank Chopp's vision for replacing the Alaskan Way Viaduct. Although you'll have to wait with bated breath for that one, here's a bit of intel about last week's mobility study that I couldn't quite fit into the column:

Last week, state, city, and county transportation officials released a "mobility study" revealing how travel times would compare between the eight remaining options for replacing the Alaskan Way Viaduct. Proponents of the “surface/transit” option were encouraged by the results, which showed that all the options, including two surface options, kept people moving through the city. An elevated viaduct produced the fastest travel times, followed by a tunnel and the surface alternatives.

Critics have pointed, however, to one major flaw in the modeling—a flaw that could lead planners to drastically overestimate downtown traffic levels in the future. In estimating how each option would effect travel times, transportation officials assumed that car trips will keep going up, up, up—by 20 percent in the next seven years. That’s in direct contradiction to the state’s stated commitment of reducing car trips—known as “vehicle miles traveled”—by 50 percent in the next 40 years. And it reflects a fundamentally flawed view of how people make their travel decisions.

Say you need to drive to the grocery store. If it’s rush hour, and you have some flexibility, you’re may decide to make your trip at another time, combine it with other errands later in the day, shop online, or take a different route. That’s because you’re human, and humans adjust their behavior to fit changing circumstances. The state’s viaduct planning model, however, assumes they never do that. Ron Paananen, the state’s viaduct project director, says state planners will “start talking about changes in demand” when they do projections for 2030—but had they considered the way people actually behave this time around, their estimates for travel times would probably have been much lower. If hurrying up traffic is no longer the most important consideration, the surface/transit option starts to look even more appealing.