Your car headrest is a safety restraint, not mainly a pillow; NHTSA tests front restraints to a maximum 55 mm backset and requires them to withstand 890 newtons for 5 seconds

Most of us tend to consider the headrest as one of the more comfortable parts of a car. We use it on long journeys to support our heads, lean back against it at a traffic light, or rest while someone else is driving. What may not come to mind is that this padded support is also a closely regulated safety feature. The National Highway Traffic Safety Administration's laboratory test procedure for head restraints, TP-202aS-01, specifies a maximum backset of 55 mm for front outboard restraints, referring to the distance between the back of the head and the front surface of the restraint. The same procedure sets requirements for height, energy absorption and structural strength.

Why the gap behind your head is more important than a cushion

It is important to consider why the 55 mm requirement exists. Neck injuries can occur in rear-end collisions, including crashes that do not necessarily involve very high speeds. During a rear impact, the seat and the occupant's torso move forward relative to the head, which can produce rapid movement of the neck. Keeping the head restraint close to the head can help limit this movement and reduce the potential for neck injury. NHTSA says the federal head-restraint standard is intended to reduce the frequency and severity of neck injuries in rear-end and other collisions.


NHTSA's testing document explains how the backset is checked in a laboratory setting. Engineers use a head restraint measurement device to establish the position of the restraint and take repeated backset measurements. The procedure records three measurements and uses their average to determine whether the restraint passes the 55 mm requirement. The procedure also specifies minimum head-restraint heights, including a minimum of 800 mm for front outboard seating positions, subject to specified roof-line exceptions.

For drivers, the practical point is that the position of the restraint matters. A restraint set too low may not provide the intended support for the head, while excessive reclining of the seat can increase the distance between the head and restraint. A useful adjustment is to position the restraint so that its upper portion provides support behind the head and neck, rather than leaving it at the setting used by the previous driver.

How a five-second strength test demonstrates a headrest's ability to protect you

Backset and height are not the whole story. A restraint also has to withstand a substantial load without failing, which is where the strength requirement comes in. According to TP-202aS-01, the head restraint must support a force of 890 newtons for five seconds. That is roughly equivalent to the weight force of a 91-kilogram mass under Earth's gravity, making the test a measure of whether the restraint can withstand a sustained load rather than a momentary push.

A separate part of the procedure covers energy absorption. Under the standard, the restraint must keep headform deceleration below 785 m/s² for more than three milliseconds when impacted at speeds up to and including 24.1 km/h. The test is designed to assess how the restraint responds when struck, rather than simply whether it can hold its shape under a static load.

Together, these requirements show that a headrest is not simply a padded surface added for comfort. Its position, height, ability to withstand force, and response to impact are all addressed by the federal testing framework before a vehicle is certified for compliance with the applicable safety requirements.

For drivers, the takeaway is much simpler than the laboratory procedure. Before setting off, check that the head restraint is positioned appropriately behind your head and that the seat is adjusted for a normal driving position. A few seconds spent checking the adjustment can help ensure that a safety feature designed and tested for head and neck protection is being used as intended.