Comments mention driving too close to the car in front, or too fast, but I'd like to bring attention to distracted drivers. You can see how late the 4th-8th car apply the brakes, and quite reluctantly too. The first couple of cars behind the Tesla did crash but at a pretty low speed, I'd say not even at airbag-deploying speed. But the 6-7th end up hitting the pileup at a good 40-50mph.