That's some unsettling footage.
Those cars the FedEx truck hit were essentially a ramp; I'd be surprised if those folks survived.
Not having been there, it's hard to say what might have prevented or mitigated that, but sudden ice is obviously a nasty thing.
On non-winter tires, sailing along, and then hitting the brakes...trajectory & time are pretty much running things.
My brother said my niece would have been there except she had the day off.
The situation, at least as my wife's coworker described it, drove in from Denton, about 30 miles at normal highway speeds, no precipitation at all, it's dark and they're in the express lanes, I think the speed limit there is 75 MPH, all of a sudden you crest a bridge and you're on ice between barriers. Not a damned thing you can do. She said she aimed for the softest thing she could pick out amongst the horrible choices she had.
