Usually southbound trains for Tide Flats will pull into the Log Yard and not go into the main BNSF yard. If its to long or things are choked up they will pull down the old main and wait. Most of the time there is a yard job that will pull the stacks over the bridge and onto the tide flats. I dont think there is alot of pressure to avoid blocking A street these days when traffic can flow nicely over the new D street bridge.
For north bound trains they do have to be pulled south down thru the yard..some times as far down as the Moon Yard to hold for nb power. If the stacks are going south (not to usual) they just move on without stopping.
Roger B