SUMMARY

As part of a vehicle's structural support system, a roof creates a "non-encroachment zone" or "survival space" that should protect occupants in a crash.  If a roof crushes substantially in an accident, occupants may suffer disabling head or neck injuries.

Most vehicles do not have enough headroom to allow for more that three to four inches of crush without significantly increasing the risk of serious injury.

Rollovers are the most common cause of roof crush.  Over 10,000 people are fatally injured each year in rollover crashes.  The causal relationship between rollovers and harm to occupants from roof crush has been recognized as early as 1932.

Nevertheless, the auto industry denies the relationship between roof crush and occupant injuries.

Manufacturers insist that the forces generated by the impact--not a lack of crashworthiness--cause the injury or death.  This argument does not take into account that rollovers are among the most benign accidents because the vehicle decelerates over a long distance.  Arguing that rollovers are random events that cannot be duplicated, manufacturers rarely conduct rollover tests to guide their roof design or construction. 

NHTSA's FMVSS 216, which sets the minimum strength requirements for a vehicle's roof crush resistance, does not require manufacturers to conduct dynamic rollover tests on roofs.  The federal standard also fails to consider what material the roof is made of and how it is constructed.  Consequently, this failure has led to:

In a rollover, a roof can crush in a number of different ways depending on the construction of the roof and the vehicle trajectory:

One of the most common types of injury in a rollover roof crush case is a neck fracture caused by flexion and shear forces produced when the roof crushes down on the occupant.

Other types of neck injuries include
axial neck compresion injuries:

and hyperextension neck injuries:

Brain injury can also occur by intrusion of the roof into the occupant space.