In addition to perception distance, reaction time and braking distance, trucks have one additional factor – brake lag. Semi-trucks have different brakes than the regular passenger vehicle. Most passenger vehicles on the road have hydraulic brakes, which are liquid, faster and more instantaneous. Semi-trucks have air brakes, which have a lag time.
Think of your garden hose and when you turn the nozzle on, the water does not automatically come out the end of the hose. Rather, you turn the nozzle, wait while the water travels, and then it comes out the end. It is the same concept with these brakes. The truck driver hits the brake, the air has to be built up and reach everywhere on the truck, and then the brakes are applied. Of course, semi’s need more distance and time just from the heavy loads alone, but they also have brake lag that plays a part.