Federal Motor Vehicle Safety Standard (FMVSS) 201 - Occupant Protection in Interior Impact - was upgraded in 1995, with a 1998-2002 phase-in, to reduce occupants' risk of head injury from contact during crashes with a vehicle's upper interior, including its pillars, roof headers and side rails, and the upper roof. Initially, energy-absorbing materials alone were used to meet the standard; later, some vehicles were also equipped with head-protection air bags. NHTSA does not yet have enough crash data to evaluate the injury-reducing effectiveness of the energy-absorbing materials. However, the agency has conducted 154 matched pairs of impact tests with free-motion headforms in pre- and post-standard vehicles of 15 selected make-models.