Alternative Roof Crush Resistance Testing with Production and Reinforced Roof Structures

The government, automotive industry and scientific community are currently scrutinizing the adequacy of the FMVSS #216 roof crush standard in the United States. As a result of concern about the ability of FMVSS #216 to enforce reasonable protection to occupants in rollovers, The National Highway Traffic Safety Administration (NHTSA) has recently published a Request For Comments in the Federal Register regarding updating this standard¹. The inverted drop test methodology is a promising alternative test procedure to evaluate the structural integrity of roofs and is being considered by NHTSA as a possible compliance test. Recent testing on many different vehicle types indicates that damage consistent with field rollover accidents can be achieved through inverted drop testing at very small drop heights. Drop tests matrices were performed on 9 pairs of vehicles representing the majority of personal transportation vehicle types. This paper offers several examples of post-production reinforcements to roof structures that significantly increase the crush resistance of the roof as measured by inverted drop tests. These modifications were implemented with minimal impact on vehicle styling, interior space and visual clearances. The results of these modifications indicate that roof intrusion protection can be enhanced by nearly an order of magnitude as roof crush was reduced by 44-89% with only a 1–2.3% increase in vehicle weight.

Research and testing indicates that the static vehicle roof crush resistance, as measured by the current FMVSS 216 test procedure, is highly dependent on glazing integrity and the angle of load application. Fractured or missing glazing and/or more lateral load applications, as typically seen in field accidents, significantly reduce the structural resistance capabilities of many automotive roof structures. Two tests are presented in which the vehicle roofs are shown to collapse significantly under their own weight when the glazing is removed and the vehicles are placed on the roofs at lateral angles beyond those described in FMVSS 216 or SAE J996.