Two runaway portal carts flipped into a dead-end here, and the crawlers grinding through righted one and kept it.
Yard M answered a question Carl had been worrying about: what happens to a rogue portal cart once it punches through the abyss gate and nobody is driving it. He had feared they would start looping endlessly up and down the tracks. Instead, a group happened to be grinding their way through yard M when the first cart arrived — the same one blaring "Physical" by Olivia Newton-John — and the switching stations automatically routed it into a dead-end parking space meant as a holding area for engine cars.
The cart ran to the end of the track and flipped. Its Debris Scoop sent the yard's entire awning system into The Abyss on the way over, and then the portal shut itself off a moment later, leaving the cart on its side with its wheels still spinning. A few minutes after that the second cart arrived and flipped as well.
The crawlers there did something Carl did not plan for and would certainly approve of: they gathered enough people to physically heave one of the two carts back upright, got it onto a track, and turned it on again. Yard M now has a working portal weapon of its own and is using it to keep at least one of the nearby tracks clear. Of the six carts Carl sent out roped with dead men's hands, this is the only one that ended up in somebody else's hands as a going concern.
A trainyard missing its awning system, with two overturned rail carts in a dead-end holding siding, one of them since righted and returned to service.
The proof of concept for a cart's afterlife: automatically parked, flipped, self-disarmed, and salvaged into a permanent defence.