SAT is a switcher that works Selkirk Auto Terminal. This usually occurs at some point in the evening hours well after (usually more than half a day) Q232 has arrived in the Top End Yard.
Power for this train moves into an available empty track at the west end of the yard. This will be the overnight WB train Q285 called at 04:00 daily.
The Top End Yard will contain quite a bit of extra autoracks from previous trains. Normally this means full empty or full loads coming in and out of SAT.
Provided unloading is complete, the switcher can move into SAT and pull out all the empties. Those empties then get shoved in behind the Q285 power and preferably an adjacent track.
Once all the empties are out of SAT, the switcher can then bring in available loads to fill up the auto terminal
from Top End Yard loaded strings. This continues until all tracks are full west of the crossing.