A.S. King interviewed at Writer Unboxed.
From the interview:
Most of my books follow this same sort of POV switch, and one of the reasons I enjoy that is because if I get bored or stumped with one POV, I can keep working on the other. Very rarely do both stump me at once. I remember having to separate the Emer & Saffron storylines to check continuity during revisions. And because I wanted things to read smoothly, I resisted my math-geek urge to have chapters mathematically structured and switched POV when it came most naturally.