One of the main reasons that a semitruck accident is so devastating for another driver is simply that the truck weighs so much more than that car. Many cars and small SUVs only weigh a few thousand pounds. When they get hit by the semi, it has so much more mass to contribute to the crash that it just tears through the smaller vehicle.
Truck drivers need to be able to communicate on the road, but they also need to be safe. To strike a balance, the Federal Motor Carrier Safety Administration (FMCSA) banned most cellphone use, but they did allow drivers to use hands-free devices in most cases.
If a truck driver falls asleep at the wheel, you now have an 80,000-pound vehicle that is completely out of control. That puts everyone at risk in a heartbeat; even just nodding off for a second can be enough to cause a deadly accident. For that matter, even a tired driver can cause a serious crash without completely falling asleep at all.