What actually causes multiple car pile-ups?

Occasionally I hear about multiple car pileups involving 30+ cars. In cases of near zero visibility this makes sense, a car ahead of you could be stalled/stopped/disabled etc... but even if you're going 5mph you can't see it and crash. But in other cases caused by distracted driving or whatever else,... show more Occasionally I hear about multiple car pileups involving 30+ cars. In cases of near zero visibility this makes sense, a car ahead of you could be stalled/stopped/disabled etc... but even if you're going 5mph you can't see it and crash.

But in other cases caused by distracted driving or whatever else, this doesn't make sense. Unless you're tailgating and/or going faster than the traffic conditions call for there is no reason for a car to rear-end into another car times 30.

News reports always give the cause for the first crash, but they never say why the other 29 cars were unable to stop quickly enough. They never say what I suspect to be the truth, that the car pile up was actually caused by mass stupidity where people think it's okay to drive above the speed limit and tailgate.
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