Concept of Whiplash Injury Lessening Seats

Toyota's Whiplash Injury Lessening (WIL) seats, Volvo's WHIPS seats, and Saab's Active Head Restraints (SAHR) are safety features designed to lower the risk of whiplash injuries.

The term 'whiplash' was first defined in 1928. It is a hyperextension injury of the neck that is mostly associated with low-velocity collisions wherein the vehicle is struck from behind. It can also occur if the vehicle stops abruptly.

Over 1 million people suffer from whiplash injuries in car accidents every year in United States, with more than $30 billion being spent on these injuries. Studies have revealed that about 70% of the people affected by a whiplash injury recover completely after one year, whereas 82% recover completely from the tissue, back, or neck injuries within two years.

The concept of Whiplash Injury Lessening seats was introduced, taking into account the increasing number of whiplash injuries. Toyota introduced the WIL concept, with the objective of protecting the driver and the passenger in the front from whiplash injuries that are commonly observed in low-velocity, rear-end collisions. It was introduced in 1997, with its effectiveness tested through computer-generated human body models, known as THUMS (The Total Human Model for Safety).

To understand how whiplash injury lessening seats work, let's first understand what happens during such an injury.

When a vehicle is struck from behind, the occupant's head is thrown backwards, which causes the lower part of the cervical spine to bend backwards. Soon after that, the head or upper part of the cervical spine bends forward. These sudden movements cause the cervical spine to stretch beyond its normal range of motion.

Neck pain and other symptoms could arise as a result of damage to the soft tissues, muscles, ligaments, and intervertebral discs during an impact. The posture at the time of collision and the stabilization response could determine the effect of such an injury. The impact can be more if the head restraint is not positioned correctly.

Insurance Institute of Highway Safety (IIHS) conducted certain studies and found that there wasn't ample protection from whiplash in rear-end collisions where the head restraints were too low or too far away from the back of the head or neck.

Toyota incorporated the whiplash injury lessening design in the driver's seat and the front passenger's seat, to reduce the forward acceleration of the torso, as well as the differential motion of head and the torso during such collisions. Let's find out how WIL seats work.

➞ The seat back has been specially designed to absorb the energy of the occupant's upper body. This occurs as the body is pulled back, and sinks deeper into the back of the seat.
➞ The seat back and the rear pre-crash safety-activated WIL headrest work together to ensure that the person on the seat has the right posture during the collision.

➞ A millimeter-wave radar device installed in the rear bumper detects the presence of a vehicle approaching from behind.
➞ The driver of the vehicle in the rear is alerted. The hazard lights flash if there's a risk of a collision.

➞ The sensors that are implanted within the front headrests move diagonally upward, and shift to appropriate positions prior to the impact.
➞ During the impact, the seat back and the headrest are closer to the head, neck, and the upper torso.

This posture allows proper support to the head and the neck, thereby preventing the cervical spine from stretching beyond its normal range of motion.

Besides Toyota's whiplash injury lessening concept seat, Volvo's WHIPS seat, and Saab's Active Head Restraint (SAHR) also serve the same purpose.

➞ In Volvo's WHIPS seat, an expandable hinge present at the base of the seat back moves the seat backwards in the event of a collision, allowing the occupant to remain in contact with the headrest.

➞ In case of SAHR, the head and neck is supported, as the head restraint moves forward and upward during the collision. The movement of the head restraint is controlled by a pressure plate in the back of the seat. It moves when the body exerts excessive pressure on the pressure plate in the back of the seat during a collision.

Studies have revealed that vehicles that have well-designed head restraints can reduce the incidence of injuries in rear-impact crashes by 24% to 44%. Automakers such as Toyota have certainly taken a right step by incorporating the concept of whiplash injury lessening seats. Hopefully, we will see other automobile manufacturers using such technologies in the future as well.