Report investigating the importance of head restraint positioning in reducing neck injury in rear impact
Section snippets
Head restraint history
Whiplash or Whiplash Associated Disorders may go unreported or not gestate until well after a crash. They do not show up in police/coroner reports because they are frequently not the cause of death and cannot be proven without dissection of the neck. The severity of neck injury may be reduced by head contact with the head restraint, making head restraint position and adjustment an important safety issue.
The installation of head restraints in the front seats of Australian vehicles has been
Head restraint measurement device
It has been widely accepted that the sooner the head contacts the head restraint the less chance there is of serious neck injury (States, 1972, Cameron, 1980, Meeting of Experts of Passive Safety, 1995).
This was the basis for the head restraint performance criterion, namely the relative vertical and horizontal distances from the standard head position of a 50th percentile adult male. Two performance criteria suggested for evaluation of vehicles with the Head Restraint Measurement Device have
Results and analysis
The results of the head restraint measurements are summarised in the Table 1 below.
The first column specifies the make and model of the vehicle. The second column specifies the head restraint type, either fixed or adjustable.
The next four columns assess the head restraints in their lowest rearmost position. First, the vertical and horizontal measurements taken using the Head Restraint Measurement Device are listed, and then the IIHS and ICBC criterion resulting from the measurements are listed.
Discussion
The measured vehicles represent a majority of the vehicles sold in Australia. The head restraint types also represent the majority available across the Australian fleet, i.e. fixed or adjustable in the vertical direction only. All the vehicles showed a significant improvement in position if adjusted. However, any possible benefit offered is not achieved if head restraints are maintained in the lowest rearmost position.
In interpreting the results, several important points need to be reinforced.
Conclusion
A properly adjusted head restraint will prevent excessive extension of the neck of a properly positioned occupant in a rear impact collision. However, head restraints are not as effective at reducing soft tissue injuries in the neck as seat back yielding. Seat back yielding appears to be the most effective means of reducing AIS 1 neck injuries. Further investigation is needed to explore the implementation of these injury-mitigating technologies.
In the study undertaken, adjusting head restraints
Future work
FORS intends to continue research into opportunities for improving head restraint effectiveness especially in areas such as horizontal offset and seat back yielding. There is also still a lack of knowledge and understanding of neck injury mechanisms, this is the major obstacle in producing an effective countermeasure.
FORS will participate in the international debate on the direction neck injury mitigation should take. ADR 22 is currently being reviewed with a view to aligning it fully with
Acknowledgements
This project would not have been completed without the assistance of several people. Keith Seyer and Craig Newland for their assistance in editing the paper. Also Mark Terrell, Matt O’Keefe and Stephen Stratton for their assistance with the head restraint measurements.
References (25)
Kinematics and dynamics of the vehicle/seat/occupant/system regarding whiplash injuries
Whiplash Injuries Diagnosis and Treatment
(1996)- Bostrom O., Autoliv Sweden, AB Research, et al., 1997. Prediction of Neck Injuries in Rear Impacts Based on Accident...
- Bostrom, O., Autoliv, AB Research et al., 1996 A New Neck injury Criterion Candidate based on Injury findings in the...
- Cameron, M.H., 1980. The Effect of Australian Design Rule 22A for Head Restraints, Department of Transport, Office of...
- Federal Office of Road Safety, 1994. ADR 3/02, Australian Design Rules for Motor Vehicles and Trailers as determined...
- Federal Office of Road Safety, 1994. ADR 22/00, Australian Design Rules for Motor Vehicles and Trailers as determined...
- Fildes, B., Vulcan, P., 1995. Neck Injury and Spinal Characteristics: Injury Outcome and Crash Characteristics in...
- Fildes, B., 1992. Crash and Injury Patterns to Australian Car Occupants, Monash University Accident Research...
Postural studies on whiplash injuries
Whiplash Injuries Diagnosis and Treatment
(1996)- Gibson, T., McIntosh, A., 1997. Rear End Impact Associated Neck Injuries. Department of Safety Science, University of...