Roof crush is the failure and displacement of an

automobile roof An automobile roof or car top is the portion of an automobile that sits above the passenger compartment, protecting the vehicle occupants from sun, wind, rain, and other external elements. Because the earliest automobiles were designed in an era ...

into the passenger compartment during a rollover accident. Every year approximately 10,000 Americans are killed in rollover accidents, accounting for about 30% of all light vehicle occupant fatalities. The number of occupant injuries is significantly higher. The relationship between injury levels and intrusion or roof crush has been statistically established, but the mechanism has been thought sometimes to be somewhat obscure. Theories advocating the idea that rollover injuries are caused by the occupants "falling" or "diving" into the vehicles interior have been advanced, but the severity of these events, and thus their potential for causing injury, has been questioned. Observations from

school bus A school bus is any type of bus owned, leased, contracted to, or operated by a school or school district. It is regularly used to transport students to and from school or school-related activities, but not including a charter bus or transit bus ...

and heavy

truck A truck or lorry is a motor vehicle designed to transport cargo, carry specialized payloads, or perform other utilitarian work. Trucks vary greatly in size, power, and configuration, but the vast majority feature body-on-frame construction ...

rollovers also suggests that the fall and dive theories are incorrect and that another theory of the mechanism of injury in rollover accidents is required, one that relates injury to the intrusion of the roof structure into the occupant compartment or more simply to "roof crush". Today it is generally realized that the primary injury mechanism in light vehicle rollover accidents is not crushing. Rather, it is widely acknowledged that the principal injury process for contained, i.e., non-ejected, occupants involves the impact between the occupant and the vehicle interior. Since the severity of an impact depends to a large extent on the

relative velocity The relative velocity \vec_ (also \vec_ or \vec_) is the velocity of an object or observer B in the rest frame of another object or observer A. Classical mechanics In one dimension (non-relativistic) We begin with relative motion in the classi ...

between the impacting objects; the impact theory of injury causation in rollovers has sought to explain the increase in injuries associated with increased roof crush with an increase in the relative velocity between the occupant and the vehicle's interior which is generated by the roof crush. In the simplest terms, when the occupants hits a collapsing roof, they hit harder because the roof is moving in on them. If the roof was not collapsing, and thus moving towards the occupants, their velocity relative to the roof would be lower and the impact less severe. Roof crush has also been identified as a cause of both full and partial ejection in rollover accidents because of ejection portals created by the collapsing roof structure. These chiefly involve broken windows but occasionally also involve the body structure. The current Federal regulation involving roof strength - 49 CFR 571.216 (FMVSS 216) - has been found to offer little benefit and is currently being reviewed. Many European manufacturers provide stronger roofs than do U.S. or Asian manufacturers despite the fact that there is no European (

EEC The European Economic Community (EEC) was a regional organization created by the Treaty of Rome of 1957,Today the largely rewritten treaty continues in force as the ''Treaty on the functioning of the European Union'', as renamed by the Lisb ...

) roof strength regulation for light vehicles. The

Volvo XC90 The Volvo XC90 is a mid-size luxury SUV manufactured and marketed by Volvo Cars since 2002 and now in its second generation. The first generation was introduced at the 2002 North American International Auto Show and used the Volvo P2 platform ...

may be a good example of this.

References

{{DEFAULTSORT:Roof Crush Automotive safety