Head restraint

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Head restraints (also called headrests) are an automotive safety feature, attached or integrated into the top of each seat to limit the rearward movement of the adult occupant's head, relative to the torso, in a collision — to prevent or mitigate whiplash or injury to the cervical vertebrae.^[1][2] Since their mandatory introduction in some countries beginning in the late 1960s, head restraints have prevented or mitigated thousands of serious injuries.^[2]

A patent for an automobile "headrest" was granted to Benjamin Katz, a resident of Oakland, California, in 1921.^[3] Additional patents for such devices were issued in 1930^[4] and in 1950,^[5] and subsequently. The major U. K. supplier of head restraints, Karobes, filed patents in the late 1950s and was still competitive in 1973 when British tests evaluated the quality of these devices.^[6]

Optional head restraints began appearing on North American cars in the mid-1960s,^{[citation needed]} and were mandated by the U.S. National Highway Traffic Safety Administration (NHTSA) in all new cars sold in the U.S. after January 1, 1969. The U.S. regulation, called Federal Motor Vehicle Safety Standard 202, requires that head restraints meet one of the following two standards of performance, design, and construction:^[2]

• During a forward acceleration of at least 8g on the seat supporting structure, the rearward angular displacement of the head reference line shall be limited to 45° from the torso reference line, or
• Head restraints must be at least 700 mm (27.6 in) above the seating reference point in their highest position and not deflect more than 100 mm (3.9 in) under a 372 N⋅m (3,292 in⋅lbf) moment. The lateral width of the head restraint, measured at a point either 65 mm (2.56 in) below the top of the head restraint or 635 mm (25.0 in) above the seating reference point must be not less than 254 mm (10.0 in) for use with bench seats and 171 mm (6.73 in) for use with individual seats. The head restraint must withstand an increasing rearward load until there is a failure of the seat or seat back, or until a load of 890 N (200 lbf) is applied.

An evaluation performed by NHTSA in 1982 on passenger cars found that "integral" head restraints—a seat back extending high enough to meet the 27.5 in (698.5 mm) height requirement—reduces injury by 17 percent, while adjustable head restraints, attached to the seat back by one or more sliding metal shafts, reduce injury by 10 percent. NHTSA has said this difference may be due to adjustable restraints being improperly positioned.^[2]