×There are only two things I've been able to accomplish:
-Pausing the red citizen by blocking the narrow hallway with a keg.
-Destroying the red station near the start. This makes the red citizen go back to his starting station, and never move.

Doing either of these just gets the green and blue citizens stuck behind the red citizen, so I can't make any further progress as far as I can tell. And I can't get close enough to do anything about the green or blue citizens. Their target stations are blocked by walls, so it doesn't look like there's any way for me to destroy them without killing citizens.

×The key was to destroy the red station sooner.