The reason this was on my mind, BTW, is because I'm coming up to the Midpoint of my own story, where Roan the MC is going to travel to an alternate reality to try and find her missing dog.
I'd initially guessed that the Decision was kind of, she chooses to go despite the danger, and maybe that's part of it. But Roan has been driven to find her dog no matter the consequences the whole story, so that doesn't quite feel like the Driver here.
Meanwhile I was writing the scene right before the Midpoint, where she makes a deal with a Witch to find out how to travel to the "right Elsewhere", the reality where her dog is. And it turned out that Roan has to find "the right tree". But what's really neat is, I didn't understand why, but the Witch just would not tell her which tree to use. To the point of getting really angry when Roan was like "I don't understand, there must be hundreds of trees in this forest, how can I know which one?"
I didn't realize it, but that makes it possible for Roan's selection of the "right tree" to be the Midpoint Driver. And it works well because OS Signpost 2 is Understanding, and the Witch was really trying to get her to understand how worlds-travelling works, so that she could select the right tree on her own. Once she does this, it should be a strong Bump into Doing: making the journey to Elsewhere, and whatever other Doing my muse throws at her once there...
But if the Witch had told her exactly which tree to use, or exactly what criteria to use to find it, it wouldn't have worked so well for a Decision driver because she wouldn't have any important choice or selection to make. That's kind of neat.