Get the impression he's responding to GR somewhat. The whole of that book eventually narrows down to the point at the tip of the rocket hanging over the world whereas this one emphasises an opening up of possibilities.
There's a scene where a character more or less lays it out in their thoughts on departing by ship. The land being reduced to a single point of arrival as you close in on the dock and the reverse being true as you leave.
There's a lot of Lines of Flight-type talk and mentions of Desire and Flows, so I reckon he's leaning on D&G a bit. Fair bit about unconventional families, gender roles and whatnot too. There's a threesome late in the story which feels like a response to Blicero, Katje and Gottfried in the earlier book as this time the three are adults, the woman is in charge and it isn't abusive.
No object or MacGuffin or anything at the centre of this one either. It's conspicuously hollow as he keeps bringing up this point about arches and gateways. I don't get the maths though, so maybe I'm missing something there. There's a lot about explosions and explosives, so the novel expanding in multiple directions from a hollow centre makes sense in that respect too.
It's not my favourite of his, but I've really enjoyed it.
There's an absolute ton on Eastern European geopolitics and geography that you get swamped with in the second half. I didn't know half the places he was referencing. You get bombarded with all these spots in the Balkans that various railways pass through and all the intrigue that comes with rival powers jostling for control of the networks.
It does feel like this one got away from him a bit. Remember Vollmann saying when he was writing YBaRA! that he just kept writing and writing and could have gone on forever and I get the same feeling from this. I reckon he could have written another thousand pages, easily. There doesn't seem to be any logical stopping point or real sense of direction. It just keeps going and going and going.