“the potential, long-term environmental impacts of the streets-and-transit option are far greater than the theoretical, short-term reduction of vehicle trips that that option is purported to create.”

This is just utterly and completely false. Its not the environmental impacts of surface/transit, its the environmental impacts of creating a N/S freeway to the East and it is a logical fallacy (without evidence) to somehow correlate these two things. Your argument is a poor attempt at scare tactics.

Furthermore your argument that a tunnel is the “long-term” solution is also entirely false. If anything has been proven over the last 100 years of the American experiment it is that freeways and SOV travel are the absolute worst solution for growing urban populations. Transit, especially rail, is far more efficient in moving people and goods.

If anything, based on the way voters have been moving in recent years I would say that it is much more likely to spark a new push for Eastside Rail than a new Eastside freeway.

Not only do the s&t promoters think car traffic will stop growing, they think car traffic will dramatically shrink. Actually, so does our Governor, who signed a bill to aim at 50% reduction in vehicle miles traveled in Washington State by 2050.

Even if vehicle use somehow goes up by 20% (I guess this assumes no peak oil, WA’s VMT reduction fails, and Priuses go on sale for $5,000), the WSDOT study reported that this option does just fine.

But I’m just copying from a much better description of the issues. For the source, take a look at Cary Moon’s wonderful piece on Hugeasscity.

Less than a year ago a surface option was preferred due to cost:
http://www.wsdot.wa.gov/NR/rdonlyres/8DE75ACA-24B0-4871-B689-7C112CF032E5/0/AWV_SAC_Nov13_Model_Analysis_Handout_lowres.pdf