Passenger cars have liquid brake systems (brake fluid) which causes liquid to immediately dispense when the brakes are activated. But did you know that tractor trailers (the big rigs, semis you see on the roadway) have braking systems that are based on air? When the brakes are pressed, the air in the chambers is compressed. Air does not escape/dispense out into the braking system with air brakes as quickly as it does in a passenger car.
(The photo to the right is taken from “Truck Troubles.com” and can be found here.)
If you couple the air braking system with the fact that these tractor trailers are extremely heavy, it simply takes longer for a semi-truck to stop as compared to a passenger car. Sometimes, aside from taking longer to stop, if the truck driver applies his/her brakes too fast and the weight in the trailer behind the truck is too much, the semi-truck will jackknife, causing a hazard to all motorists on the roadway.
I have written about the dangers of distracted driving as it relates to passenger cars and motorcycles multiple times. You can find such postings here, here, and here. Considering the fact that from the moment a commercial truck driver first sees a road hazard it could take 7 seconds, or even longer to stop, avoiding distractions while driving a tractor trailer becomes crucial to avoid truck crashes.