A train that runs directly to a cluster of stairwell stations — the shortcut off the floor Widget points the party toward.
The Escape Velocity is a named train on The Iron Tangle that, Widget scoffs, goes straight to a gaggle of stairwell stations — the very thing Carl's party has been struggling to reach the hard way. The gremlin mechanic explains the route: take a Tangerine-line train up to station 89 and transfer onto the Escape Velocity for a direct run to a cluster of exit stairwells. It reframes the party's whole approach to leaving the floor, suggesting the maze of lines has clean shortcuts for anyone who knows the system.
An Iron Tangle line-train (undescribed in detail) that serves a direct route to a bundle of stairwell stations.
A shortcut train to the floor's exit stairwells, revealed by Widget as the easy way out.
Also appears in books you've already read — spoiler-safe to their endings: