In an automobile

Automobile

An automobile, autocar, motor car or car is a wheeled motor vehicle used for transporting passengers, which also carries its own engine or motor...

, head restraints are attached or integrated into the top of the seats

Car seat

A car seat is the chair used in automobiles. Most car seats are made from inexpensive but durable material in order to withstand as much use as possible.-Ergonomy: Lumbar and thigh support:...

 in each seating position to limit the rearward movement of an adult occupant's head relative to his torso in a crash, so as to reduce the danger of whiplash

Whiplash

Whiplash may refer to:* The long flexible part of a whip* Whiplash , an injury-Film and television:* Whiplash , a 1948 American film noir* Whiplash , a Hong Kong film starring Cheng Pei-pei...

 or other injury to the cervical vertebrae

Cervical vertebrae

In vertebrates, cervical vertebrae are those vertebrae immediately inferior to the skull.Thoracic vertebrae in all mammalian species are defined as those vertebrae that also carry a pair of ribs, and lie caudal to the cervical vertebrae. Further caudally follow the lumbar vertebrae, which also...

. Since their mandatory introduction in the late 1960s, head restraints have prevented or mitigated thousands of devastating injuries.

A patent for an automobile "headrest" was granted to Benjamin Katz, a resident of Oakland, California

Oakland, California

Oakland is a major West Coast port city on San Francisco Bay in the U.S. state of California. It is the eighth-largest city in the state with a 2010 population of 390,724...

, in 1921. Additional patents for such devices were issued in 1930 and in 1950 , and subsequently.

Head restraints started to appear as an option on American cars in the late 1960s, and were mandated by the U.S. National Highway Traffic Safety Administration

National Highway Traffic Safety Administration

The National Highway Traffic Safety Administration is an agency of the Executive Branch of the U.S. government, part of the Department of Transportation...

 (NHTSA) in all new cars sold in the U.S. starting 1 January 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:

• 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 then 100 mm (3.9 in) under a 372 N·m (3,292 in·lbf) moment
  Moment of inertia
  In classical mechanics, moment of inertia, also called mass moment of inertia, rotational inertia, polar moment of inertia of mass, or the angular mass, is a measure of an object's resistance to changes to its rotation. It is the inertia of a rotating body with respect to its rotation...
  
  . 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 in) above the seating reference point must be not less than 254 mm (10 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 (1,962 lb) 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 injuries by 17 percent, while adjustable head restraints, attached to the seat back by one or more sliding metal shafts, reduce injuries by 10 percent. NHTSA suggests this difference may be due to adjustable restraints being improperly positioned.

Most head restraints are cushioned for comfort, may be adjustable for height and rotative position, and are commonly finished in the same material as the rest of the seat.