Head restraints identification of Issues Relevant to

Table 6.2 Vertical Position of Top of Head Restraint With Respect to Top of Occupants Ear

	At or Above Ear	Below Ear
Adjustable	59%	41%
Integral	77%	23%

A visual determination was also made of whether the driver’s head was within 4 inches horizontally of the head restraint (Table 6.3). For adjustable head restraints 69 percent were touching or within 4 inches of the driver’s head. Twenty-nine percent of these restraints were greater than 4 inches from the occupant’s head. An assessment could not be made for 2 percent of cases. Seventy-seven percent of the integral head restraints surveyed were touching or within 4 inches of the driver’s head. Twenty percent of these restraints were greater than 4 inches from the occupant’s head. Three percent could not be assessed.

Table 6.3 Backset of Head Restraint With Respect to Rear of Occupants Head

	0" - 4"	> 4"	Unknown
Adjustable	69%	29%	2%
Integral	77%	20%	3%

As mention in section 2.1, Kahane [19] estimated that 75 percent of adjustable restraints were left in the down position. In the current survey it was determined that 47 percent of adjustable restraints were left in their lowest position (Fig. 6.1). Twenty-six percent of these were sufficiently high to have the top of the restraint above or at the top of the ear. Fifty-one percent of adjustable restraints were not in their lowest position. Thirty percent of these were below the top of the ear. Two percent of all adjustable restraint cases could not be assessed.

6.2 Occupant/Head Restraint Position Survey Analysis

To get a sense of the combined vertical and horizontal position of the surveyed head restraints, each was placed in Class A, B or C (Table 6.4). The classes correspond to the restraint’s position or potential position referenced to the driver’s head. A head restraint was placed in Class A when: (1) the top of the head restraint was at or above the top of the occupant’s ear, and (2) the head restraint was less than four inches away from the rearmost portion of the occupant’s head. A head restraint located too far away from the occupant’s head and/or too low could potentially allow rearward and/or angular displacement between the head and neck before the head contacts the restraint. Thus, restraints in Class A, potentially, offer better whiplash prevention. A head restraint was placed in Class B if, when observed, it was not positioned to meet criteria (1) and/or (2), but appeared capable of being adjusted to meet them by raising the head restraint or reducing the seat recline angle. Class C restraints appeared not capable of being positioned to meet criteria (1) and/or (2).
Fifty-three percent of the surveyed adjustable head restraints were in Class A. An additional 19 percent were in Class B with the remaining 28 percent in Class C. For integral restraints, 70 percent were in Class A, 30 percent in Class C and none in Class B.
Table 6.4 Overall Classification of Head Restraint Position

	Class A	Class B	Class C
Adjustable	53%	19%	28%
Integral	70%	0%	30%

Based on the overall survey results the following observations can be made.
1. Three quarters of head restraints were adjustable.

2. Half of the adjustable restraints were left in the “down” position. Three quarters of these could have been raised to increase the potential whiplash protection.

3. Of the restraints that were vertically adjusted, thirty percent required further adjustment to increase the potential of whiplash protection.

4. A greater percentage of integral head restraints than adjustable head restraints were positioned to provide increased potential for whiplash protection. With proper positioning a similar percentage of adjustable restraints could achieve the same level of potential effectiveness.

Other qualitative observations were apparent from the survey. For example, many newer vehicles (MY 1990+) had a rotating feature that allowed the restraint to be in closer proximity to the occupant’s head. Many occupants adjusted the restraint to fit behind the neck. Consumers may not perceive the head restraint as a protective device, but simply as a head rest or pillow. In addition, the newer vehicle head restraints appeared to be more upright and closer to the occupant than in previous models. In older model vehicles (MY 1980's & older), the head restraints tended to follow the seat back angle.

6.3 Head Restraint Height Survey

To obtain a rough estimate of head restraint heights at the driver’s position for late model vehicle, a small number of vehicles were sent to the Vehicle Research and Test Center (VRTC) in Ohio. VRTC measured the maximum and minimum heights using the procedure defined in FMVSS 202. The sample consisted of 20 vehicles: 14 PCs and 6 LTVs. The results for each vehicle are shown in Appendix D. The averages are contained in Table 6.5. Of the 14 PCs measured, 11 had adjustable restraints. Of the six LTVs measured, three had adjustable restraints. On average, the LTV integral restraints were 0.9 inches over the 27.5 inch requirement of FMVSS 202. The PC integral restraints were 2.3 inches above the required height. The adjustable restraints for the LTVs and PCs achieved similar average maximum heights at about 1.3 inches over the requirement. The average adjustment ranges were 1.7 and 2.1 inches for LTVs and PCs, respectively.

Table 6.5 Average Head Restraint Heights From 20 Vehicles (inches).

	LTV	PC
			Min.	Max.	Min.	Max.
Adjustable	27.1	28.8 (n = 3)	26.8	28.9 (n = 11)
Integral	----------	28.4 (n = 3)	----------	29.8 (n = 3)

Note: n = sample size.

6.4 Estimate of 1995 Fleet Composition

Kahane [19, pg. 114] reported that for PCs in model years 1969 - 1981 the percentage of integral restraints varied between 9% and 39%, with the value in 1981 being 33%. To obtain a rough estimate of the distribution of integral versus adjustable head restraints in the front outboard positions of recently manufactured vehicles the sales figures for the 1995 top 20 selling PCs and LTVs were acquired [2]. The restraint type for each model was determined by observation at vehicle dealerships. Although some models had both types of head restraint available, depending on the trim-line, only the type most commonly observed was used. Appendix E contains the sales data and restraint type for each model. The top 20 sales leaders accounted for 50 and 76 percent of total 1995 sales for PCs and LTVs, respectively. Table 6.6 shows the restraint type distribution. The data clearly indicate that, in newer vehicles, PCs typically have adjustable restraints and LTVs typically have integral restraints. However, when lumped together there is about an even split between the two restraint types.
Table 6.6 Estimated Head Restraint Type Distribution for

Top 20 Selling 1995 MY PCs and LTVs

	Adjustable	Integral
PC	88%	12%
LTV	21%	78%
Total	53%	47%

7.0 IIHS’s Evaluation of Head Restraints

In November 1995, the Insurance Institute for Highway Safety (IIHS) published the report, Measurement and Evaluation of Head Restraints in 1995 Vehicles, [6]. The head restraints in 164 vehicles were measured: five were rated as good, eight acceptable, 34 marginal and the remaining 117 as poor.
The head restraint evaluations were based on two criteria: the height of the restraint and its horizontal distance from the back of the head (backset). Both of these variables were measured relative to the head of a seated average-size male, as represented by a specially designed head form mounted on a standard H-point machine. The H-point machine was seated in accordance with FMVSS No. 208 S11.4.3.1 and the seat was adjusted to achieve a torso angle of 25 degrees from vertical.
The vertical reference value used in the evaluation of each head restraint was the distance from the top of the head to the head’s center of gravity. The vertical reference measurement of 9 cm was taken from the 50th percentile adult male dummy drawing [1]. The height of a head restraint was rated as “marginal” if the restraints top was 9 ± 1 cm below the top of the head form. The vertical rating was “good” if the distance from the top of the head form to the top of the restraint was less than 6 cm (i.e. the top of the head restraint was at least 3 cm above the head’s center of gravity). Table 8.1 shows the dimensions for each rating.
The reference value used to evaluate backset was 10 cm. This is from a study by Olsson [26], mentioned in section 4.2, that showed a statistical relationship between the backset and the duration of neck symptoms. The backset of a restraint was rated as “marginal” if the horizontal distance between the head form and restraint was 10 ± 1 cm. The backset was rating as “good” if the distance was less than 7 cm. A restraint’s overall rating was the lower of the height and backset scores.
Table 8.1 IIHS Head Restraint Rating Dimensions

	Height Rating	Backset Rating
	Top of Head Form to Top of Head Restraint	Back of Head Form to Head Restraint
Good	< 6 cm	< 7 cm
Acceptable	7 ± 1 cm	8 ± 1 cm
Marginal	9 ± 1 cm	10 ± 1 cm
Poor	> 10 cm	> 11 cm

IIHS first evaluated adjustable restraints in their lowest position. If the restraint manually locked in its “up” position it was also evaluated in that position. If IIHS determined that a restraint would possibly lock under dynamic loading, the restraint was evaluated in its “up” position. The overall rating of adjustable restraints were lowered one category to reflect the likelihood that many occupants would not adjust the head restraint. Restraints that did not lock manually or dynamically in the up position received a score based on the measurements for the “down” position.
It should be pointed out that the IIHS head restraint ratings were based on geometric values only and were not correlated with either injury claims or injury rates for those specific make-models. Such an analysis may verify the geometric value rating of the vehicles.

8.0 European Standard

The European analogue to FMVSS 202 is Economic Commission for Europe (ECE) Regulation No. 25. In its current form the regulation requires all forward facing outboard seats to have head restraints. FMVSS 202 only requires restraints in the front outboard seats. Regulation No. 25 requires integral head restraints to have a 29.5 inch height above the H-point. Adjustable restraints must be able to achieve this height, but cannot be any lower than 27.5 inches in any position of adjustment. The achievable height specified by ECE No. 25 is 2 inches higher than required by FMVSS 202. Further, FMVSS 202 has no minimum limit for the range of adjustment.
In May of 1996, a proposal was accepted to phase-in raised head restraint height requirements for front outboard seats and raised minimum head restraint height requirements for all outboard seats. The phase-in period is 48 months, after which front head restraints must be able to achieve a height of 31.5 inches. Adjustable head restraint in front and rear seats cannot be any lower than 29.5 inches. These new provisions result in a required achievable head restraint height four inches above that required by FMVSS 202. The minimum acceptable height will be 2 inches higher than the required achievable height in FMVSS 202.

9.0 Ongoing NHTSA Research on FMVSS No. 207, Seating Systems

In addition to the research project sponsored at UVA (see section 3.3.3), NHTSA is funding the development of a generic integrated safety seat by EASi Engineering (EASi) and Johnson Controls (JCL), Inc. EASi is subcontracted to JCL to build and test the prototype for safety requirements. The designed integrated seat will be for a production vehicle and the safety requirements will exceed the current FMVSS requirements including FMVSS 202. A report on the final design will be placed in the Docket during the Fall of 1996. Prototypes may be designed and tested in consultation with the agency.

10.0 Future Head Restraint Designs

A variety of new head restraint designs have been proposed in an effort to reduce whiplash by improving the relative position of the head and head restraint. The “Cervigard” is a form fitting passive head restraint which attempts to be in close proximity to and support the entire head/neck complex [39].
Another proposed head restraint uses proximity sensors to track the occupant head during normal driving [28]. Electrical motors then automatically position the head restraint vertically and horizontally. During a rear impact the restraint is passive. A patent is pending on the device.
Delphi Interior and Lighting Systems has developed the Pro-tech active head restraint (Appendix F). During normal driving the head restraint can be adjusted as desired by the occupant. During a rear impact the force of the occupants torso on a pressure plate in the seat structure forces the restraint forward and upward. The developers believe this deployment process will occur rapidly enough to limit the relative motion of the head and torso resulting in a reduction in whiplash injuries. The first commercial application of the patented device will be in the 1997 Saab 9000. The Pro-tech head restraint is part of a total seat system called the “Catcher’s Mitt”. The “Catcher’s Mitt” promises high retention of the occupant during a rear impact by providing energy absorption in transverse deforming seat back cross members. The deforming lower seat back cross member produces a pocketing of the occupant’s pelvis and lower back in the deforming seat back padding which resists ramping as well as attenuates occupant loading.

11.0 Identification of Safety Issues

The purpose of a head restraint is to prevent whiplash injury of the neck in rear-impact crashes. There are several open questions related to the protection provided by head restraints.
(1) Are existing restraints sufficient in preventing neck injuries in rear impacts? How can head restraints and seating systems be improved to reduce neck injuries? What means should be used to measure improvements?
(2) Is the height requirement sufficient? Should there be a requirement for the horizontal distance between the head and head restraint? Should adjustable head restraints have to lock in position?
(3) If the FMVSS 202 height requirement is changed, should the alternate dynamic procedure be changed to maintain equivalence between the compliance options? Is a dynamic test procedure a necessity for active head restraints? Is the current knowledge base in neck injury criteria sufficient to extend the performance requirements of the dynamic procedure? Would changes to the Hybrid III neck have to be made?
(4) In response to the 1982 Evaluation [19], one commenter opposed higher restraint height requirements due to the potential decrease of occupant visibility. Can a solution be reached which considers visibility and injury prevention?

(5) The current European Community head restraint height requirements exceed FMVSS 202 and they are proceeding with increased height requirements. Should this provide the bases for a change in the U.S.?
(6) In what way could an upgrade of FMVSS No. 207, Seating Systems, affect requirements for head restraints? Should any change in FMVSS No. 202 be synchronized/ integrated with changes in FMVSS 207?

17. 
    Foret-Bruno, J.Y.; Dauvilliers, F.; Tarriere, C. (1991): Influence of The Seat and Head Rest Stiffness on the Risk of Cervical Injuries in Rear Impact. Proc. 13th ESV Conf. in Paris , France, paper 91-S8-W-19, US DOT, NHTSA, HS 807 991.
    

18. 
    Jakobsson, L.; Norin, H.; Jernstrom, C.; Svensson, S.E.; Johnsen, P.; Hellman, I.I.; Svensson, M.Y. (1994): Analysis of Head and Neck Responses in rear end impacts - a new human-like model. Volvo Car Corporation Safety Report.
    

19. 
    Kahane, D.J. (1982): An Evaluation of Head Restraint - Federal Motor Vehicle Safety Standard 202. NHTSA Technical Report, DOT HS-806 108, National Technical Information Service, Springfield, Virginia 22161.
    

20. 
    Matsushita, T. et al. X-Ray Study of the Human Neck Motion Due to Head Inertia Loading. Proc. of 38th STAPP Car Crash Conference, 1994.
    

21. 
    McConnell, W.E.; Howard, R.P.; Guzman, H.M.; Bomar, J.B.; Raddin, J.H.; Benedict, J.V.; Smith, H.L.; Hatsell, C.P. (1995): Human Head and Neck Kinematics After Low Velocity Rear-End Impacts - Understanding “Whiplash.” SAE Paper 952724, Proc. Of 39th STAPP Car Crash Conf.
    

22. 
    Mertz, H. J.; Patrick, L. M. (1967): Investigation of the Kinematics and Kinetics of Whiplash. Proc. 11th STAPP Car Crash Conf., Anaheim, California, USA, pp. 267-317, LC-67-22372
    

23. 
    Mertz, H. J.; Patrick, L. M. (1971): Strength and Response of the Human Neck. SAE Paper 710855, Proc. 15th STAPP Car Crash Conf.
    

24. 
    Nilson, G.; Svensson, M.Y.; Lovsund, P.; Viano, D.C. (1994): Rear-End Collisions - The Effect of Recliner Stiffness and Energy Absorption on Occupant Motion. Dept. of Injury Prev., Chalmers Univ., Gotegorg, Sweden, ISBN 91-7197-031-2.
    

25. 
    Nygren, A.; Gustafsson, H.; Tingvall, C. (1985): Effects of Different Types of Headrests in Rear-End Collisions. Proc. 10th ESV Conf., pp. 85 - 90, NHTSA, HS 806 916.
    

26. 
    Olsson, I.; Bunketorp, O.; Carlsson, G.; Gustafsson, C.; Planath, I.; Norin, H.; Ysander, L. (1990): An In-depth Study of Neck Injuries in Rear-end Collisions. 1990 International IRCOBI Conference on Biomechanics of Impacts, pp. 269-280, Bron-Lyon, France
    

27. 
    Ono, K and Kanno, M. (1993): Influences of the Physical Parameters on the Risk to Neck Injuries in Low Impact Speed Rear-End Collisions. 1993 International IRCOBI Conference on Biomechanics of Impacts, pp. 201-212, Eindhoven (The Netherlands).
    

28. 
    Rachmilevitch, A. (1996): Anti-Whiplash Protection. Proc. 29th Int. Symposium on Automotive Technology and Automation, Florence, Italy, pp. 535-541.
    

29. 
    Ruedemann, A.D. (1957): Automobile Safety Device - Head Rest to Prevent Whiplash Injury. Journal of the American Medical Association, Vol. 164, pp. 1189.
    

30. 
    Schneider, L.W.; Foust, D.R.; Bowman, B.M.; Snyder, R.G.; Chaffin, D.B.; Abdelnour, T.A.; Baum, J.K. (1975) Biomechanical Properties of the Human Neck in Lateral Flexion. SAE Paper 751156, Proc. of 19th STAPP Car Crash Conf.
    

31. 
    Severy, D.M.; Brink, M.H.; Baird, J.D. (1968): Backrest and Head Restraint Design for Rear-End Collision Protection. SAE Paper 680079.
    

32. 
    Simons, J. (1989): Final Regulatory Evaluation: Extension of Head Restraint Requirements to Light Trucks, Buses, and Multipurpose Passenger Vehicles with Gross Vehicle Weight Rating of 10,000 Pounds or Less, Federal Motor Vehicle Safety Standard 202. NHTSA Technical Report, DOT HS
    

33. 
    States, J. D.; Balcerak, J. C.; Williams, J. S.; Morris, A. T.; Babcock, W.; Polvino, R.; Riger, P. And Dawley, R. (1972 ): Injury Frequency and Head Restraint Effectiveness in Rear-End Impact Accidents. Paper 720967. Proc. of 16th STAPP Car Crash Conf., 1972.
    

34. 
    Svensson, M. Y. and Lovsund, P. (1992): A Dummy for Rear-End Collisions - Development and Validation of a New Dummy Neck. Proc. 1992 International. IRCOBI Conf. On the Biomechanics of Impacts, pp. 299-310, Verona, Italy
    

35. 
    Svensson, M.Y.; Aldman, B.; Lovsund, P.; Haland, Y.; Larsson, S. (1993): Rear-End Collisions - A Study of the Influence of Backrest Properties on Head-Neck Motion Using a New Dummy Neck. SAE paper no. 930343.
    

36. 
    Svensson, M.Y.; Aldman, B.; Lovsund, P.; Haland, Y.; Larsson, S. (1993): The Influence of Seat-Back and Head-Restraint Properties on the Head-Neck Motion During Rear-Impact. Proc. 1993 Int. IRCOBI Conf. On the Biomechanics of Impacts, Eindhoven, The Netherlands, pp. 395-406.
    

37. 
    Svensson, M.Y.; Aldman, B.; Lovsund, P.; Hansson, H. A.; Seeman, T.; Sunesson, A.; Ortengren, T. (1993): Pressure Effects in the Spinal Canal during Whiplash Extension Motion - Possible Cause of Injury to the Cervical Spinal Canal Ganglia. Proc. 1993 International IRCOBI Conference On the Biomechanics of Impacts, Eindhoven (The Netherlands)
    

38. 
    Viano, D.C. (1992): Restraint of a Belted or Unbelted Occupant by the Seat in Rear-End Impacts. SAE paper no. 922522, Proc. 36th STAPP Car Crash Conf., pp. 165-178.
    

39. Automotive Industries: Vol. 175, April, 1995, pp. 76.

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