[UPDATE: To be clear, I'm not saying a bus/rail transfer is necessarily a bad idea, especially if congestion on I-5 gets much worse. I'm saying if you're going to do it you might as well do it at Rainier Beach.]
Late last year I did a back-of-the-envelope calculation for bus-rail transfers at Rainier Beach, which everyone agrees is not an optimal setup. The outcome of that analysis was that sending buses to Rainier Beach instead of downtown cost the baseline rider 8 minutes while saving about $4.4m a year, savings that could be reinvested in more frequent buses. This time gap could decrease significantly in bad traffic or if the final destination was far north of Sodo, but increases with the walking and wait time associated with a transfer.
Various people in the know have suggested S. 133rd St. as a possible station site, one that would provide more direct access for freeway buses and save even more operating costs. However, Google Maps (and the 150 schedule) suggests an unimpaired I-5 bus takes about 12 minutes to get from S. 133rd St. to Sodo Station; the Link schedule plus some interpolation suggests Link would take 20 minutes. Although someone with more analysis chops can prove me wrong, the time penalty appears to be the same 8 minutes. The 5 minutes it would take a bus to drive from Interurban to Rainier Beach is the same 5 minutes it takes the train to cover the same distance.
Of course, the bus savings would be larger; on the other hand, Sound Transit would have to spend at least tens of millions to actually build the station. And of course, you’d be increasing travel times on Link by a few minutes as well. If there’s any real engineering analysis of this station, I haven’t seen it, but the initial look is not promising at all.