If the driver knew there was black ice around, and drove in a way that he encountred black ice and ran over perople because he couldn't stop , then I think he should be held criminally negligent.

If it was sudden black ice, where its raining or drizzling and then it suddenly freezes over (this happened to me and it is not fun at 70mph on the freeway) with no warning, then you can truly say it was an act of god and there was no criminal negligence.