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Car Seat Design and Whiplash

A team of Volvo researchers assessed the risk factors influencing whiplash-related injuries, and prepared guidelines for improving car seat and neck restraint design as a means to decrease injury. They stress risk factors are both design- (seating position, and restraint use) and occupant- (gender, height, rear or front seat occupant) related.

After taking into consideration the differing theories of injury mechanisms, the researchers developed the following guidelines for future design: 

  • Reduce occupant acceleration.
  • Minimize relative movements between adjacent vertebrae and in the occipital joint, i.e. the curvature of the spine shall change as little as possible during the crash.
  • Minimize the forward rebound into the seat belt.

They explain that the reduction of acceleration is just a basic assumption—if a zero acceleration is achieved, no injury will result. Keeping the spine as evenly supported and intact as possible will avoid injuries, and since seatbelt interaction has been suggested as injury-producing, they aspire to reduce the rebound after impact.

In applying these guidelines in a practical design form, the researchers imply the seatback and head restraint should geometrically support the curvature of the back and neck—this can be achieved by positioning the structures as close as possible to the occupant. Also, no structure in the seat should force the spine into a localized bending position; the seat should follow the shape of the occupant well and properly. Finally, they suggest the implementation of good energy absorption of the seat backrest. The authors explain, "In other words, designing the seat towards lower elastic energy build-up during impact will reduce the forward rebound into the belt."
The researchers than conducted various testing and mathematical simulations, with positive and applicable findings:

"We believe that using this method will result in a new seat design reducing the risk of neck injuries. An important factor, also due to the nature of the biomechanical guidelines, is that no negative consequences will be introduced...In conclusion, the result of the various tests, and the mathematical occupant simulations, show that the new seat design has considerable potential for offering a reduced risk of neck injuries in rear end impacts."

Lundell B, Jakobsson L, Alfredsson B, Jernstrom C. Guidelines for and the design of a car seat concept for improved protection against neck injuries in rear end car impacts. Society of Automotive Engineers 1998; SAE 980301.