Weird sequence. I'm positioned just north of the North Market Interlocking on the TRRA Merchants Sub in North St. Louis.
The Amtrak train came across the river from Illinois and stopped where it is in this photo. Then, the ballast train on the left came across the river and stopped right next to the Amtrak train.
Then, the Amtrak train went forward through the interlocking, followed by the ballast train. Not sure why the Amtrak train had to stop in the first place.