Under GCOR, what must a conductor do when the train's movement will cause another car or engine to foul (block) a main track?

1. Proceed immediately, as main track fouling is permitted during yard switching
2. Obtain permission from the dispatcher before allowing any movement that will foul the main track
3. Sound the horn three times to warn other crews before fouling the main track
4. Post a lookout on the main track and proceed with the fouling movement