Originally posted by sigma:
If the car had not been where it was, not only would a significant percentage of the momentum of the truck have not been absorbed, but the truck also wouldn't have veered sharply, affecting its' impact with the bus. The bus would have absored 100% of the force at dead-on its' rear. Instead of being pushed 200 feet due to a momentary impact, it would have been pushed several hundred feet at least as the truck embedded itself into the rear of the bus.


Actually, a car of any size would absorb very little of the momentum of a full size 18-wheeler going at a high speed, hardly a "significant percentage". The car being there was pretty insignificant in regards to stopping the truck.

If you want figures... let's assume the truck weighs 60,000 pounds and was going 60 mph, and the car was 4,000 pounds. We don't know exactly how much the truck weighed, but even a truck with an empty trailer weighs well over 40,000 pounds, and the gross weight limit is about 80,000 so the median is a good estimte. Using those assumptions, then after impact, the car and truck lodged together, and were still going over 56 mph. The car absorbed about 6% of the truck's momentum.

Just think about it... at the moment of impact, the truck decelerated a tad, and the car simultaneously accelerated to 56 mph almost instantaneously, and subsequently smashed into the bus. I don't even want to calculate how much G-force that would be... poor kids.

It may or may not be true that the truck then collided directly with the bus. However, the bus would in no circumstance have absorbed 100% of the momentum of the truck, given the fact that the truck still weighs at least twice as much a school bus. Had the truck and car also been embedded into the back of the bus, it would not have traveled 200 feet, but in fact would have gone a much lesser distance.

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