multi-car crashes: a question

There's something I've been wondering about for a while. It's on my mind now because I was in a long online chat with someone at GEICO. I was getting Sharon added to my car insurance, since she just got her license. I asked the agent my question and he didn't know the answer. Big sad.

When there's a car accident, the relevant insurers have to come to a determination of who is at fault, or who shoulders what percent of the fault. They do this by reviewing police reports and whatever other information there is. Maybe they question the drivers. I assume there are various formulae to cover the more common situations.

But what about those freaky hundred-car pileups on frozen interstates in winter? Every so often you read about those. How on earth do the insurance companies figure out who to blame? I work in insurance, but I'm a life actuary, and car insurance is a P&C line. And, besides, I doubt that assessing the damage and assigning blame is part of what the property-casualty actuaries do.

If anyone knows, please answer in the comments. Thanks.