When a passenger vehicle collides
with the rear end or side of trucks, trailers or buses not equipped with
effective guards (bumpers), it continues to travel beneath the taller chassis
of the larger vehicle, i. e., the passenger vehicle "rides under" the larger
one. The invasion of the passenger compartment that follows the underriding
causes severe head and upper body injuries in the car occupants and consequently
results in a very high rate of fatality. Often the car passengers are decapitated,
when occurs the so called "guillotine effect".