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In January 2011, the National Highway Traffic Safety Administration (NHTSA) published a final rule establishing Federal Motor Vehicle Safety Standard (FMVSS) 226 Ejection Mitigation, with the intent of reducing the occurrence of complete and partial ejections of vehicle occupants during crashes, especially rollover events. FMVSS 226 requires component-level tests to be conducted on ejection mitigation countermeasures (e.g., rollover-activated side curtain airbags). A guided, linear impactor is used to propel a headform into a rollover-activated countermeasure at up to four locations for each side daylight opening in the vehicle, for up to three seating rows. The impact tests are conducted at two energy levels (speeds) and associated impact times: 278 J (20 km/h) at 1.5 s after curtain activation and 178 J (16 km/h) at 6 s. The FMVSSS 226 compliance criterion is that the headform cannot travel more than 100 mm past the inside surface of the side window plane.

In this paper, the concept of ridedown analysis is extended to provide the total occupant energy and ridedown energy as functions of time. The difference between the total occupant energy and the energy absorbed by the front structure represents the energy which is dissipated by deforming the components of the restraint system. This analysis allows an improved understanding of the restraint system as a whole, and how its components interact with each other and with the front structure of the car to dissipate the occupant's energy throughout the crash event.