GitHub - muppet9010/factorio-belt-braid-sinner: Punishes those who commit one of the true sins, belt braiding.
Detail: The small wall at underground belts is smaller, when a belt is side loading it, visualizing, that one side of the belt can now in the underground. : r/factorio
Underground belt side loading (Belt Madness) - Factorio Forums
An example of the "underground belt trick" for compressing output : r/ factorio