The color-line intersecting Station 149 that the party plans to ride toward the Nightmare Express and stop 436.
The Purple Line is a color-coded route intersecting the ochre line at Station-149. It figures in Carl's route plan: after derailing the ochre train, he and Princess-Donut intend to take the purple line to station 283 and catch the Nightmare-Express — a rare looping train — to investigate the mysterious stop 436, one past the colored lines' 'end' at 435, then loop back to the red/yellow station 83 if it's a bust.
A purple-coded route on the Iron Tangle's subway maps.
A planned leg of the party's route toward the Nightmare Express and stop 436.