The relationship between occupant crash injury and occupant compartment intrusion is seen in the perspectives of the velocity-time analysis and the NCSS statistical data for two important accident injury modes, lateral and rollover collisions. Restraint system use, interior impacts, and vehicle design features are considered. Side impact intrusion is analyzed from physical principles and further demonstrated by reference to staged collisions and NCSS data. Recent publications regarding findings of the NCSS data for rollovers, as well as the NCSS data itself, are reviewed as a background for kinematic findings regarding occupant injury in rollovers with roof crush. The findings in both modes are consistent with the proposition that occupant injury is related to occupant-interior velocity history, rather than intrusion per se, for all but the most violent crashes, and that any association seen between injury and intrusion is likely a mutual manifestation of crash severity, rather than a cause-effect relationship between intrusion and injury. Indeed, intrusion may have beneficial, detrimental, or neutral effects upon injury, depending upon seating position and restraint.
Attempts to stiffen vehicle structures as a means of controlling intrusion will succeed as injury prevention measures only if they accomplish a meaningful moderation of the velocity history of the contacted surface relative to the occupant - otherwise they may be counterproductive.