HEAD RESTRAINTS -

Identification of Issues Relevant to

Regulation, Design, and Effectiveness

National Highway Traffic Safety Administration

Office of Crashworthiness Standards

Light Duty Vehicle Division

November 4, 1996

TABLE OF CONTENTS

Executive Summary iv

1.0 Review of FMVSS No. 202 1

1.1 Requirements/Background 1

1.2 Rulemaking Chronology 1

1.2.1 Establishment of FMVSS No. 202, Head Restraints for Passenger Cars
(PCs) 1

1.2.2 Notice of Proposed Rulemaking (NPRM) to Incorporate FMVSS No. 202
into FMVSS No. 207 2

1.2.3 Expansion of FMVSS No. 202 to Trucks, MPVs & Buses 2

1.2.4 Clarification of Test Procedure for Head Restraint Strength 2

2.0 Previous Regulatory Evaluation 3

2.1 Passenger Car Evaluation 3

2.2 Light Truck Evaluation 4

3.0 Biomechanical Aspects of Neck Injuries and Head Restraint Design 4

3.1 Neck Anatomy and Range of Motion 4

3.2 Pathology of Whiplash 6

3.3 Head Restraint and Seat Design as Related to Neck Injury Mechanisms
6

3.3.1 Historical Perspective on Head Restraint Height Requirement 6

3.3.2 Current Perspectives on Head Restraint Positioning and Neck Injury
7

3.3.3 Seat Back Stiffness and Neck Injury 8

3.3.4 Neck Injury Criteria and Dummy Necks 9

4.0 Evaluation of Real-World Crashes 11

4.1 Estimated Cost of Whiplash 11

4.2 Injury Rate and Duration and Contributing Factors 12

4.3 NASS Data for Front Outboard Occupants in Rear Impacts 12

4.3.1 Whiplash Rate by Head Restraint Type, Vehicle Type, and Occupant
Gender 13

4.3.2 Passenger Car Whiplash Rate by Occupant Height and Gender 14

4.3.3 Passenger Car Whiplash Rate by Occupant Age 16

5.0 Review of ODI's Consumer Complaint File 17

6.0 Survey of Restraint Positioning and Fleet Composition 19

6.1 Occupant/Head Restraint Position Survey Results 19

6.2 Occupant/Head Restraint Position Survey Analysis 21

6.3 Head Restraint Height Survey 22

6.4 Estimate of 1995 Fleet Composition 23

7.0 IIHS's Evaluation of Head Restraints 23

8.0 European Standard 25

9.0 Ongoing NHTSA Research on FMVSS No. 207, Seating Systems 25

10.0 Future Head Restraint Designs 25

11.0 Identification of Safety Issues 26

References 28

Appendix A 32

Appendix B 34

Appendix C 36

Appendix D 38

Appendix E 41

Appendix F 43

Executive Summary

I. Current Head Restraint Regulation

Since January 1, 1969 passenger cars have been required by FMVSS No. 202
to have head restraints in the front outboard seating positions. Head
restraints must be at least 27.5 inches above the seating reference
point in their highest position and not deflect more than 4 inches under
a 120 pound load. Optionally, they must not allow the relative angle of
the head and torso of a 95th percentile dummy to exceed 45 degrees when
exposed to an 8 g acceleration. FMVSS 202 was extended to light trucks
and vans under 10,000 pounds on September 1, 1991.

In 1982 NHTSA reported the effectiveness of integral and adjustable
restraints at reducing neck injuries in rear impacts was 17 and 10
percent, respectively. The difference was due to integral restraints
being higher with respect to the occupants head than adjustable
restraints, which are normally left down. It was concluded that head
restraints were a cost effective safety device.

II\. Whiplash Pathology

The term whiplash refers to the motion of the head and neck relative to
the torso and the associated neck injuries occurring when a vehicle is
struck from the rear. Symptoms of pain in the head, neck, shoulders, and
arms may be associated with damage to muscles, ligaments and vertebrae,
but in many cases no lesions are evident using non-invasive means. Onset
of symptoms may be delayed and may only last a few hours, however in
some cases effects of the injury may last for years.

III\. Whiplash Biomechanics and Seat Design

A. Historical Perspective

A historical examination of head restraint height requirements indicates
that the focus has been the prevention of neck hyperextension. The
predecessor to FMVSS 202 was GSA Standard 515/22 which applied to
vehicle purchase by the U.S. Government and went into effect on October
1, 1967 \[8\]. It required that the top of the head restraint achieve a
height 27.5 inches above the H-point. Also in 1967, research by Severy
et al.,\[31\] using staged 30 mph crashes concluded that a restraint 28
inches above the H-point was adequate to prevent neck hyperextension of
a 95th percentile male. Kahane \[19\] theorized that a 50th percentile
male was adequately protected by a 27.5 inch high head restraint because
it was likely to reach the base of the skull. However, Kahane also
speculated that a 31 inch high restraint was more than twice as
effective than a 28 inch high restraint at reducing injury.

B. Current Perspective

Current research supports the contention that hyperextension may not be
necessary for whiplash to occur. Low speed staged impacts performed by
McConnell et al.,\[21\] indicate that mild whiplash symptoms can occur
without exceeding the normal range of motion. Animal research at
Chalmers University in Sweden suggests that the rapid head/neck motion,
within the normal range, cause spinal canal pressures to damage nerve
ganglia \[37\]. In contrast Mertz and Patrick \[22\] showed that 44 mph
impacts can be sustained without injury if no relative motion occurs
between the head and torso. A Volvo study reported that when vehicle
occupants involved in rear crashes had their heads against the head
restraint during impact no injury occurred \[18\]. The same study
related a rear impact simulation computer model to actual accident data
and identified the rate of volume change in the cervical spinal canal as
a possible predictor of whiplash injury. Other predictors identified
were neck shear force, neck tensile force and head angular acceleration.
Another study of Volvos involved in rear impacts showed that a
significant increase in injury duration occurred when the occupant's
head was more than 4 inches away from the head restraint \[26\].

Several computer modeling studies have shown that seat design features
other then head restraint geometry affect the likelihood of neck injury.
Simulating impacts consistent with FMVSS 301 (ΔV = 32 km/h), Nelson et
al.,\[24\] showed that increasing recliner stiffness is likely to reduce
whiplash injury and occupant rebound velocity can be controlled by the
extent of plastic deformation in the seat recliner. Simulating similar
rear impact velocities, researchers at the University of Virginia found
occupant-to-seat friction a highly determinate factor in ramping of the
occupant. They also concluded that increasing seat back stiffness would
reduce ramping. Simulating much lower speed impacts (ΔV = 12.5 km/h =
7.8 mph), Svensson et al.,\[35\] found that a stiffer seat, in
combination with modification to upholstery, reduced head/torso
displacement.

IV\. NASS Data Analysis (1988 - 1994)

A. Whiplash Cost

It is estimated from the National Accident Sampling System (NASS) data
that between 1988 and 1994, 742,340 whiplash injuries (non-contact AIS 1
neck) occurred annually in passenger cars (PCs), light trucks, and vans
(LTVs). The average cost (excluding property damage) of such an injury
is \$6,045 \[5\], resulting in a total annual cost of \$4.5 billion.
Thus, a small improvement in the effectiveness of head restraints could
yield large monetary savings.

B. Front Outboard Adult Occupants in Tow-away Rear Impacts

NASS data from 1988 - 1994 show that in tow-away rear impacts the injury
rate for LTVs and PCs is 16.4 and 29.8 percent, respectively (see Table
4.2). However, the sample size for LTVs is much smaller and possibly
less accurate. For PCs the difference in injury rate by restraint type
is 3.3% (32.5 - 29.2), with integral restraints having a higher rate.

For PCs the injury rate for females is slightly higher than for males
with a difference of 1.4 percent (30.4 - 29.0). When PC occupants are
segmented by gender and height the injury rate for males increases for
increasing height (Fig. 4.2). For females the trend is for injury rate
to decrease with increasing height, but at half the rate of the male
increase. The combined male-female data show an increase in injury rate
with age of PC occupant.

V. Head Restraint Position Survey and Fleet Composition

A. Relative Position of Head and Head Restraint

The Insurance Institute for Highway Safety (IIHS) evaluated the head
restraints of 164 vehicles based on their position relative to the
H-point \[6\]. Scores were reduced for adjustable restraint under the
assumption that they typically are not adjusted properly. Eight percent
of restraints were given an acceptable or better rating. Twenty-one
percent were rated marginal and 71 percent as poor.

NHTSA performed a survey of the relative position of occupant's heads
and head restraints on 282 vehicles. The tops of 59 percent of
adjustable restraints were at or above the occupant's ear (Table 6.2).
For integral restraints the value was 77 percent. Sixty-nine percent of
adjustable restraints had a backset of less than 4 inches (Table 6.3).
This value was 77 percent for integral restraints. In general, a larger
percentage of integral restraints were positioned to decrease whiplash
potential. Half of adjustable restraint were left down. Three quarters
of these could have been raised to decrease whiplash potential (Fig.
6.1).

B. Fleet Composition

Using 1995 sales data for the top 20 PCs and LTVs, the percentage of
integral and adjustable head restraints was estimated (Table 6.6).
Nearly 90 percent of PCs have adjustable restraints. By contrast nearly
80 percent of LTVs have integral restraints.

VI\. European Standard

The European analogue to FMVSS 202 is Economic Commission for Europe
(ECE) Regulation No. 25. By the year 2000 this regulation will require
front outboard seating positions to have a head restraint that can
achieve a height of 31.5 inches above the H-point (4 inches above FMVSS
202). The minimum height at all seating positions will be 29.5 inches
above the H-point.

1.0 Review of FMVSS No. 202

1.1 Requirements/Background

Since January 1, 1969, passenger cars have been required by Federal
Motor Vehicle Safety Standard (FMVSS) No. 202 to provide head restraints
that meet specified requirements for each designated front-outboard
seating position. On September 1, 1991, FMVSS No. 202 requirements were
extended to trucks (LTs), multipurpose passenger vehicles (MPVs), and
buses with a gross vehicle weight rating (GVWR) of 10,000 pounds or
less. The standard requires that either of two conditions be met:

> 1.) During a forward acceleration of at least 8g on the seat
> supporting structure, the rearward angular displacement of the head
> reference line shall be limited to 45° from the torso reference line;
> or
>
> 2.) The head restraint must measure at least 27.5 inches above the
> seating reference point, with the head restraint in its fully extended
> position. The width of the head restraint, at a point 2.5 inches from
> the top of the head restraint or at 25 inches above the seating
> reference point, must not be less than 10 inches for use with bench
> seats and 6.75 inches for use with individual seats. The head
> restraint must withstand an increasing rearward load until there is a
> failure of the seat or seat back, or until a load of 200 pounds is
> applied. When the load reaches 120 pounds, the portion of the head
> form in contact with the restraint must not exceed a rearward
> displacement (perpendicular to the extended torso reference line) of 4
> inches.

Two types of head restraints have been utilized to meet the requirements
of FMVSS No. 202:

> [Integral head restraints]{.underline} \-- This system consists of a
> seat back high enough to meet the 27.5 inch height requirement. There
> is a variety of integral head restraint designs (Appendix A).
>
> [Adjustable head restraints]{.underline} \-- This system consists of a
> separate head restraint pad that is attached to the seat back by
> sliding metal shaft(s). The occupant may adjust the restraint to the
> top, bottom, or intermediate positions. Some restraints allow angular
> rotation (Appendix A). The angular adjustment feature allows the
> occupant to adjust the restraint closer to the rearmost portion of the
> head.

1.2 Rulemaking Chronology

1.2.1 Establishment of FMVSS No. 202, Head Restraints for Passenger Cars
(PCs)

Effective January 1, 1969, each passenger car manufactured on or after
that date had to comply with the requirements of FMVSS No. 202 \[9\].
The standard required a head restraint for the driver position and right
front seating position to reduce the frequency and severity of neck
injury in rear-end and other collisions. The restraint was intended to
limit rearward motion of an occupant's head in a rear impact crash,
thereby preventing whiplash or neck sprain injury due to hyperextension
of the neck.

1.2.2 Notice of Proposed Rulemaking (NPRM) to Incorporate FMVSS No. 202
into FMVSS No. 207

On March 19, 1974, a NPRM (Docket No. 74-13; Notice 1) was published in
the Federal Register \[10\]. The NPRM proposed to: (1) extend
applicability of FMVSS No. 202 to multipurpose passenger vehicles
(MPVs), light trucks, and bus driver seats manufactured after September
1, 1976; (2) establish barrier crash testing for cars, MPVs, and light
trucks; and (3) consolidate FMVSS No. 202 with 207 because of the
relationship between head restraints and seats.

On March 16, 1978, a Notice of Request for Public Comment (Docket No.
78-07; Notice 1) invited public comments on a draft plan for the motor
vehicle safety and fuel economy rulemaking of the National Highway
Traffic Safety Administration (NHTSA) over the five year period
1980-1984 \[11\]. A review of the active dockets revealed that a number
of actions were not completed either because limited resources were
directed toward higher priority actions, the magnitude of the problem
was not large, or NHTSA was unable to adequately document the nature and
extent of the problem. A listing and brief discussion of each of the 13
actions which the Agency contemplated terminating were presented. The
NPRM (Docket No. 74-13, Notice 1) was included on the list.

On April 26, 1979, NHTSA published the "Five Year Plan for Motor Vehicle
and Fuel Economy Rulemaking, Calendar Years 1980-1984\" which confirmed
the termination of the 1974 FMVSS No. 207 upgrade and FMVSS No. 202
consolidation \[12\].

1.2.3 Expansion of FMVSS No. 202 to Trucks, MPVs & Buses

On September 25, 1989, a notice of Final Rule (Docket No. 88-24; Notice
2) was published in the Federal Register extending the applicability of
FMVSS No. 202, "Head Restraints," to trucks, multipurpose passenger
vehicles, and buses with gross vehicle weight rating of 10,000 pounds or
less \[14\]. The expanded applicability of FMVSS No. 202 became
effective September 1, 1991.

1.2.4 Clarification of Test Procedure for Head Restraint Strength

Pursuant to the President's March 4, 1995 "Regulatory Reinvention
Initiative," a Final Rule was published in the Federal Register to
clarify a test procedure in FMVSS 202 \[15\]. The test procedure for
head restraint strength made reference to the "rearmost portion of the
head form." This phrase was replace with "any portion of the head form
in contact with the head restraint."

2.0 Previous Regulatory Evaluation

2.1 Passenger Car Evaluation

"An Evaluation of Head Restraints, Federal Motor Vehicle Safety Standard
202\", by Charles Kahane, NHTSA, February 1982, estimated the
effectiveness of head restraints in reducing the overall risk of injury
in rear impacts at 17 percent for integral head restraints and 10
percent for adjustable head restraints. These estimates were based on
Texas State accident files from 1972, 1974 and 1977. The data did not
record the type of injury so it was not possible to determine head
restraint effectiveness in reducing whiplash.

Kahane estimated that 75 percent of adjustable restraints were left in
the down position based on observation and evaluation of studies done
from 1971 to 1973 \[19, pg.108\]. An analysis of data from the National
Crash Severity Study (NCSS) showed that the in-use median height of
adjustable head restraints was less than 26 inches. By contrast, the
median height of integral head restraints was over 28 inches \[19,
pg.259\]. Since the median height of pre-standard seat backs was about
22 inches, adjustable head restraints, in effect, provided only
two-thirds as much additional height as integral head restraints. This
difference in height was believed to be the dominate factor causing
integral restraints to be more effective in reducing injury than
adjustable restraints.

The lifetime cost of integral and adjustable head restraints was
calculated to be \$12.33 and \$40.44, respectively, in 1981 dollars
\[19, pg.39\]. Because of their superior ability to reduce injuries and
lower cost, integral restraints eliminated 5.6 times more injuries per
dollar than adjustable restraints. It was further determined that the
total range of cost effectiveness for head restraints was 1020 injuries
eliminated per million dollars spent for drivers with integral
restraints, down to 60 injuries eliminated per million dollars for
passengers with adjustable restraints (Table 2.1). In comparison, it was
estimated that for a million dollars it is reasonable for society to
expect the elimination of 460 - 1500 whiplash injuries. The upper bound
of this estimate was calculated by considering medical costs, lost
wages, and legal and insurance administrative costs. The lower bound was
calculated by considering liability payments including compensation for
pain and suffering and economic losses. Clearly, there was considerable
overlap between the expected costs and benefits for drivers with
integral head restraints. For passengers with integral restraints the
confidence bounds shown in Table 2.1 overlap the range of expected
benefits.

Table 2.1 Cost Effectiveness of Head Restraints \[19\].

  ---------------------- ------------------------- ----------------------
  Position/Restraint     Injuries Eliminated per   Confidence Bounds
  Type                   \$Million                 

  Driver/Integral        1020                      490 - 1580

  Passenger/Integral     360                       160 -540

  Driver/Adjustable      190                       60 - 320

  Passenger/Adjustable   60                        20 - 110
  ---------------------- ------------------------- ----------------------

2.2 Light Truck Evaluation

The NHTSA Final Regulatory Evaluation (FRE), [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]{.underline} \[32\],
indicated that when FMVSS 202 was issued in 1968, light truck sales were
not as large a fraction of the under 10,000 pounds GVWR vehicle market
as they were in 1989. In 1970, light trucks comprised 15.7 percent of
the combined passenger car and light truck market, compared to 28.7
percent in 1985. The changing trends in light truck use and sales
resulted in the agency deeming it appropriate to determine whether some
of the safety standards originally applied only to passenger cars should
be extended to other vehicles.

The FRE discussed comments received in response to the NPRM extending
FMVSS No. 202 to trucks, buses, and MPVs with GVWR of 10,000 pounds or
less \[13\]. Several commenters recommended that integral head
restraints be required because they had been shown to have a higher
overall effectiveness. The NHTSA Office of Plans and Policy is schedule
to perform an effectiveness analysis for head restraints in light trucks
in the 1997 Fiscal Year .

3.0 Biomechanical Aspects of Neck Injuries and Head Restraint Design

3.1 Neck Anatomy and Range of Motion

The skeletal structure of the neck is comprised of seven cervical
vertebrae defining the top of the spine between the thorax and skull.
The vertebrae are numbered from C1 to C7 as they descend the neck. The
C1 vertebra is named the atlas and provides the bearing surface upon
which the skull rests. The superior surface of the atlas and the
occipital condyles of the skull form a synovial joint. This joint allows
up/down movement of the head which is exemplified by the 'yes' gesture.
Another synovial joint is formed by the atlas and the axis (C2
vertebra). This allows rotation of the head from left to right about the
axis of the neck exemplified by the "no" gesture. The remainder of the
vertebrae are separated by fibrocartilaginous discs. The vertebrae are
tied together by many anterior (front) and posterior (rear) ligaments
which run the length of the spinal column. The skull, torso and
vertebrae are connected by multiple muscle which are symmetric about the
midsagittal plane. Movement of the head with respect to the torso is
provided by these muscles.

The following terms are used to describe neck kinematics. The term
flexion refers to the combined translation and rotation of the head/neck
complex forward and down in the midsagittal plane. Extension is the
movement rearward and down in the same plane. Lateral flexion is the
translation and rotation of the head/neck complex in the medial lateral
or transverse plane. Rotation is as described above. If the prefix
"hyper" is used with these terms it means motion beyond the normal or
voluntary range.

A study using 100 subjects between the ages of 18 and 23 years reported
the average voluntary range of motion as shown in columns two and three
of Table 3.1 \[4\]. Columns four and five show the average voluntary
range of motion from another study which used 61 subjects between the
ages of 18 and 24 \[30\]. The combined flexion plus extension range is
lower for the second study. However, direct comparison of such data must
be made with caution because of variations in measurement techniques.

Table 3.2 shows the average voluntary range of motion in the midsagittal
plane (flex. + ext.) reported in two studies for males and females in
three age groups \[30, 16\]. The study represented by columns two and
three show a greater range of motion across all ages and sexes. The
trend for both studies is for decreasing range of motion with increased
age and for females to have a greater range of motion than males for all
except the 18-24 year age group.

Table 3.1 Average Voluntary Range of Neck Motion, Deg.

  ---------------- ------------------------- ------------------------- ------------------------- -------------------------
                   Subjects 18-23 yrs. \[4\]                           Subjects 18-24 yrs.       
                                                                       \[30\]                    

                   Male                      Female                    Male                      Female

  Flexion          66                        69                        \-\-\-\-\-\-\-\-\-\-\--   \-\-\-\-\-\-\-\-\-\-\--

  Extension        73                        81                        \-\-\-\-\-\-\-\-\-\-\--   \-\-\-\-\-\-\-\-\-\-\--

  Flex. + Ext.     139                       150                       129                       124

  Total Lateral    \-\-\-\-\-\-\-\-\-\-\--   \-\-\-\-\-\-\-\-\-\-\--   86                        86

  Total Rotation   \-\-\-\-\-\-\-\-\-\-\--   \-\-\-\-\-\-\-\-\-\-\--   149                       150
  ---------------- ------------------------- ------------------------- ------------------------- -------------------------

Table 3.2 Average Voluntary Total Midsagittal Head Motion, Deg.

  -------------- -------------- -------------- -------------- --------------
                 Study \[16\]                  Study \[30\]   

  Subject Age    Male           Female         Male           Female

  18-24          138            138            129            124

  35-44          109            122            103            105

  62-74          94             99             77             84
  -------------- -------------- -------------- -------------- --------------

3.2 Pathology of Whiplash

The term "whiplash" was first used in 1928 to describe neck injuries
caused by traffic accidents \[33\]. Whiplash or neck sprain is not
thought to be a contact injury in that it is not caused by a blow to the
neck, but rather by the motion of the head and neck relative to the
torso. Damage to the muscle, ligaments, and vertebrae of the neck are
consistent with whiplash. In general, the injuries do not lend
themselves to radiological assessment \[22\]. However, magnetic
resonance imaging (MRI) may be more effective identifying lesions \[3\].
Some symptoms are neck and head pain, vertigo, and dysphagia (difficulty
in swallowing). Involvement of the cervical nerves and spine often lead
to symptoms in the head, shoulder, arms or upper back. Onset of symptoms
may take hours or days and may last hours or years.

3.3 Head Restraint and Seat Design as Related to Neck Injury Mechanisms

3.3.1 Historical Perspective on Head Restraint Height Requirement

In a 1957 study, a head restraint design was proposed to minimize neck
injury. The study proposed that a padded 6-inch fixed head restraint be
attached to the top of automobile seat backs for neck protection \[29\].
The General Services Administration (GSA) Standard 515/22 [Head
Restraints for Automotive Vehicles]{.underline} , went into effect in
October of 1967 for vehicles purchased by the federal government \[8\].
It required that the head restraint be adjustable to 27.5 inches above
the H-point and be between 1 and 4 inches behind the torso line. The
preamble of the final rule contains no details as to the selection of
these parameter, but states that this standard, along with the other GSA
automotive standards were "developed through consultation with
Government agencies, the medical profession, trade associations,
technical societies, and the automotive industry".

In 1967 Severy et al.,\[31\] performed 12 full scale dynamic rear impact
crash tests using pairs of identical Ford sedans at impact speeds of 10,
20, 30, 40 and 55 mph. Seat back heights of 22 and 25 inches were used
along with seat backs and seat back/head restraint combinations of 28
inches. Seat heights were measured from the undeformed seat surface
along the seat back. This was believed to be equivalent to measuring
from the H-point. In part, the research was aimed at determining the
"lowest seatback consistent with effective protection from
whiplash\...". It was concluded that a 28 inch seat back provided
"adequate protection against the injury producing forces of most
rear-end collisions\...", even for 95th percentile males. Results showed
that in a 30 mph impact, with a 28 inch seat and the test dummy
positioned with a 3 and 6 inch backset, the test dummy's rearward head
rotation was 16 and 24 degrees, respectively.

Kahane presented anthropometric information to support the idea that a
27.5 inch head restraint provides adequate support for the head and neck
of a 50th percentile male (70 inch tall) \[19\]. Adequacy of height was
measured against the restraint's presumed ability to reduce whiplash
caused by neck hyperextension. Kahane made the following assumptions.

> "*A head restraint or seat back should come close to achieving its
> full benefit if it is high enough to reach beyond the top of the
> occupants neck - i.e., up to the skull. Additional seatback height
> would provide little additional restraint. The seatback would provide
> little or no protection if it fails to reach even the bottom of the
> occupant's neck. If the seat back reaches somewhere between the top
> and bottom of the neck, it would presumably give an intermediate
> amount of protection".* \[19, pg 251\]

Kahane theorized through a statistical model for a 70 inch occupant;
since a) the erect seating height to the base of the skull of a 50th
percentile male is about 27.5 inches above the chair base; b) people
slouch between 0 and 2.5 inches; and c) the length of the neck is about
4 inches, head restraint with heights below 22 inches have almost no
benefit and above 27.5 inches have almost full benefit.

3.3.2 Current Perspectives on Head Restraint Positioning and Neck Injury

During the mid-to-late 1960\'s, as the GSA head restraint standard was
being developed and implemented, the aim of the standard and research of
the era seemed focused on the reduction of whiplash due to
hyperextension. Current research supports the contention that
hyperextension or hyperflection may not be necessary for whiplash to
occur.

McConnell et al., \[21\] performed a series of low speed (ΔV 3.6 - 6.8
mph) staged rear end crash tests using volunteer test subjects (males 32
to 59 yrs.). The tops of the subjects' heads were 6.3 to 7.9 inches
above the tops of the head restraints and backset was 2.0 to 4.6 inches.
No cervical motion beyond voluntary range of motion was observed.
However, all subjects exhibited whiplash symptoms such as mild neck
awareness, head aches, and muscle soreness that lasted a few minutes to
a few days. Matsushita et al., \[20\] had similar results in sled tests,
with ΔV 1.6 - 3.0 mph, using male and female subjects. Matsushita also
offered an analysis of the kinematics of volunteers with
stooped-shoulder posture which suggests that upward motion of the head
relative to head restraints is not entirely reliant on the torso sliding
along the plane of the seat back (ramping), but rather on straightening
of the spine's curvature. This was also thought to cause compression in
the cervical spine.

In contrast to the findings in \[21\] and \[20\], Mertz and Patrick
\[22\] showed that a sled acceleration simulating a 44 mph rear
collision can be withstood with little discomfort if the subject's head
is initially placed against a flat head rest and the seat is rigid. This
result indicates that neck injuries may be significantly reduced during
rear impacts if the head is prevented from moving rearward relative to
the torso in the midsagittal plane.

Svensson et al.,\[36\] performed sled impacts at ΔV = 12.5 km/h (7.8
mph) on modified production seats using a Hybrid III dummy with a Rear
Impact Dummy (RID) neck (see section 3.3.4 for discussion on RID neck).
The surface of the head restraint was flat and vertical with its top
above the head C.G. (50 mm below top of head). They found that reducing
the backset from 100 mm (3.9 in.) to 40 mm (1.6 in.) caused a reduction
in maximum head/torso angle from 33 to 12 degrees and head acceleration
from 30.9 to 18.6 g.

In a recent study by Ono and Kanno \[27\], neck loads were calculated
for human volunteers during rear impact (ΔV 1.2 - 2.5 mph) sled tests
with varying head restraint heights and seat angles. Tests were run with
a "standard" head restraint (center of restraint at head C.G. height), a
"low" head restraint (center of restraint at C1 vertebra), and with no
head restraint. For all test cases the bending moment sharply increased
when rotation angles were still small. This may have been due to
resistance from cervical muscles, which could damage soft tissue. Head
rotation, bending moment, and axial load were smallest with the standard
head restraint. The highest shear force, axial force, and bending moment
were found with the low head restraint. In the case of no head
restraint, the shear force on the neck was the lowest, but the head
rotational angle was the largest, resulting in cervical hyperextension.

In a study by Volvo, a computer model (MADYMO 2D) was developed of a
seated occupant with a mechanically equivalent spine \[18\]. The effect
of head restraint position, body lean and seat inclination were
investigated for a rear impact (ΔV = 11.2 km/h = 7 mph). Ramping and
straightening of the spine occurred. Results were used to determine
which measured parameters best predicted injury by correlation with real
world injuries. Shear and tensile force in the neck along with head
angular acceleration were identified as good predictors of injury. Also,
the time derivative of the volume in the cervical spinal canal or "flow"
was thought to be a good predictor of injury potential.

3.3.3 Seat Back Stiffness and Neck Injury

A French study \[17\] using an accident data base containing 8000
involved vehicles concluded that as seat backs have become stiffer, head
restraints have become more effective at reducing neck injuries. When
seat backs are weak and break upon rear impact the head restraint may
not become involved in altering occupant kinematics.

Nilson et al.,\[24\] assessed the effect of seat recliner stiffness and
energy absorption on occupant kinematics and neck loading using a MADYMO
model. A Hybrid III dummy was modeled with a RID neck. Rear impacts up
to a ΔV of 32 km/h (20 mph) were modeled, approximating the impact
required by FMVSS 301. The seat back was modeled with recliner
stiffnesses linearly increasing with angular deflection. The "medium"
stiffness was 87 Nm/degree (770 in-lbs/deg.). The "weak" and "stiff"
seats had half and twice the stiffness of the "medium" seat,
respectively. The three linear unloading stiffnesses used in the model,
ranged from completely elastic to completely plastic. The model seat was
described as having a "high" head restraint, but no dimensions were
given. The results showed that increases in recliner stiffness resulted
in a probable increase in occupant protection as measured by head/torso
angle, C1 neck moment and head acceleration. The results improved more
between the "weak" and "medium" seats than between the "medium" and
"stiff" seats. The "medium" stiffness seat, with a minimum yield
strength of 1.5 KN-m (13,300 in-lbs), was believed sufficient to prevent
the occupant from ramping out of the seat as measured against a 60
degree limit proposed by Viano \[38\]. The chest rebound velocity of the
dummy increased with the elasticity of the unloading phase regardless of
the loading phase stiffness.

Under contract to NHTSA the University of Virginia (UVA) has developed
and applied a production seat MADYMO computer model in support of an
ongoing FMVSS No. 207 rulemaking. The final report will be placed in the
Docket. The agency will consider the results of this when deciding
whether to continue or terminate the rulemaking action of two ongoing
petitions on FMVSS No. 207. The study assessed the influence of
parameters such as dummy size, dummy/seat friction and seat stiffness on
dummy kinematics. The study concluded that increasing the amount of
rearward torque a seat back can withstand to 30,000 in-lbs at 30 degrees
of deflection should reduce occupant ramping. The model also found the
amount of ramping to be dependent on the seat friction value used.
Ramping may reduce the effectiveness of head restraints by causing the
occupants head to be farther above the restraint.

Svensson et al. \[35\] performed sled tests at low speeds (ΔV = 12.5
km/h = 7.8 mph) with a Hybrid III and RID neck on production seats. The
head restraint tops were adjusted to eyebrow level. The elastic rebound
of the seat was found to increase the relative velocity of the head and
torso if the torso rebounded forward while the head was still moving
rearward. Svensson also made modifications to production seats to
improve whiplash protection \[36\]. The surface of the head restraint
was made flat and vertical with its top above the head C.G. Increases in
seat back stiffness increased head/torso displacement slightly. However,
a stiffer seat combined with a stiffer lower-back cushion and a deeper
upper-back cushion reduced head/torso displacement. This combination of
changes eliminated the horizontal gap between the head and head
restraint in the initial phases of the impact.

3.3.4 Neck Injury Criteria and Dummy Necks

The accurate assessment of the ability of a head restraint to reduce
whiplash injuries requires both valid neck injury criteria and a dummy
with properly instrumented, biofidelic neck. The extent to which human
volunteers can be used to develop neck injury criteria is obviously
limited, so the precise mechanisms of whiplash injury remain unknown.
Based on cadaver and very limited volunteer tests, Mertz and Patrick
\[23\] recommended occipital condyles tolerance levels for neck
extension in a 50th percentile male (Table 3.3).

Table 3.3 Proposed Tolerances for Male Neck Extension by Mertz and
Patrick

  ------------------------------------- ---------------------------------
                                        Study \[23\]

  Torque                                48 Nm

  Shear                                 845 N

  Axial Tension                         1000 N

  Axial Compression                     1110
  ------------------------------------- ---------------------------------

An animal study performed at Chalmers University in Sweden indicated
that pressure changes in the cervical spinal canal may cause whiplash
symptoms even if the voluntary range of motion is not exceeded \[37\].
Live pigs were exposed to rapid extension-flexion motion of the cervical
spine while the spinal canal pressure at various location were measured.
Histopathological examination of the animals revealed injury to the
nerve-root region of the cervical and upper thoracic spine. The
researchers theorized that due to the rapid pressure change the
incompressible cerebra-spinal fluid had no where to go and stressed the
surrounding tissue. The same injury mechanism is possible in humans, so
an effective head restraint must stop head motion before the spinal
canal pressures reach an injury threshold. A quantitative assessment of
the human injury threshold could not be extrapolated from these data.

A NHTSA study evaluating non-contact inertial loads on the head-neck of
cadavers is currently underway. The Medical College of Wisconsin (MCW)
has completed construction of a cart and pendulum mechanism to evaluate
frontal, rear, and side neck injuries (Appendix B). Testing has begun
and is expected to continue through the 1998 fiscal year as specimens
become available. There are plans to perform a series of rear impact
tests with head restraints in a variety of positions. Since the
specimens lack neck musculature, development of full whiplash injury
criteria is not expected. Rather, the study will add to the body of
knowledge in the head/neck kinematics of rear impact.

Test dummies have been used in the dynamic evaluation of head restraints
since the 1960\'s and the biofidelity of the results has been in
question for just as long \[31\]. Some of the data obtained in the MCW
study along with volunteer data from the Naval Biodynamics Laboratory
\[7\] have been used in the development of an improved biofidelic neck
for a new crash test dummy being funded by NHTSA. A prototype neck is
being tested at the MCW facility. The entire dummy will be undergoing
field testing from June 1996 to June 1997. Some researchers have
surmised that the current Hybrid III dummy neck lacks biofidelity in
rear impact tests. Foret-Bruno \[17\] found that it registered excessive
shear loads when little or no relative motion between the head and torso
occurred. Svensson and Lovsund believed the Hybrid III neck to be too
stiff in the midsagittal plane and developed the Rear Impact Dummy (RID)
neck for use with the Hybrid III \[34\]. The neck has a mechanical
representation of C1 - T2 vertebrae and has been validated against
volunteer data.

4.0 Evaluation of Real-World Crashes

4.1 Estimated Cost of Whiplash

Whiplash injuries are classified as minor injuries (AIS 1) on the
Abbreviated Injury Scale (AIS) since they pose a relatively low threat
to life. However, due to their high incidence rates and often long-term
consequences, whiplash injuries can be associated with high societal
costs.

To estimate the total cost of whiplash per year in the U.S. requires an
accurate value for the cost per injury and the total number of injuries.
The National Accident Sampling System - Crashworthiness Data System
(NASS CDS) collected data on both towaway and non-towaway crashes until
1986. Columns two and three of Table 4.1 give the average annual number
of whiplashes during the period from 1982 - 1986 in towaway and
non-towaway crashes. For both PCs and LTVs the ratio of towaway to
non-towaway whiplashes is 75%. Columns four and five of Table 4.1
provide the average annual number of whiplash injuries in towaways
occurring from 1988 - 1994. Assuming 75% ratio between whiplashes
occurring in towaway and non-towaway crashes for 1988 - 1994, it is
estimated that 742,340 whiplashes occurred annually for PCs and LTVs
combined. This estimate may be conservative because many cervical
injuries, including whiplash, occur in unreported accidents \[3\]. In
addition, even when the accident is reported, whiplash may not be, due
to its delayed onset.

Table 4.1 Annualized Whiplash Injuries (AIS 1) from NASS

  -------------- -------------- -------------- --------------------- ---------------------
                 1982 - 1986                   1988 - 1994           

                 PC             LTV            PC                    LTV

  Towaway        217,599        27,962         265,173               53,183

  Non-Tow        290,068        37,066         \-\-\-\-\-\-\-\-\--   \-\-\-\-\-\-\-\-\--
  -------------- -------------- -------------- --------------------- ---------------------

According to 1994 NHTSA estimates, when the most severe injury to an
occupant is an AIS 1 injury to the face, head or neck the cost is
\$5,893 per person \[5\]. This estimate excludes property damage and
travel costs, but includes medical, legal, insurance, productivity and
work costs. Converting this to 1995 dollars, the cost is \$6,045.
Projecting this figure nationally for the estimated number of whiplash
injuries, the total monetary cost is \$4.5 billion \[\$6,045 x 742,340\]
annually.

4.2 Injury Rate and Duration and Contributing Factors

A review of Japanese insurance data showed that in 1991 more than 50% of
the injuries in car-to-car accidents were to the neck \[27\]. This was
up from a level of 44% in 1985. Ninety-five percent of injuries in rear
impacts were AIS 1 in 1991. Seventy-eight percent of the rear impact
injuries were to the neck and 95% of these were whiplash. A review of
rear impacts in Sweden showed 10% of occupants with neck pain after an
accident have symptoms which persist for five years \[25\]. The risk of
medical disability was 10% for AIS 1 neck injuries and only 0.1%
non-neck AIS 1 injuries. In a 1987 study of rear impact accidents in
Volvos, 29 of 33 occupants suffered whiplash symptoms \[26\].

Olsen et al.,\[26\] determined that a statistically significant increase
in duration of injury occurred when the occupant's head was more than 10
cm (4 in.) away from the head restraint. Forty percent had symptoms for
longer than three months. In another study of Volvos, when the occupant
pushed against the seat back and head restraint prior to impact, thus
reducing the backset distance to zero, no injury occurred \[18\].
However, Nygren et al.\[25\] did not find backset of the head restraint
to increase the rate of neck injury. Rather, he determined that the
farther the top of the head restraint is below the top of the occupants
head the greater the risk of injury. This is consistent with the 1981
analysis of Kahane who, based on Texas accident data, speculated that a
head restraint 31 inches above the H-point is more than twice as
effective at reducing overall injury than a head restraint 28 inches
above the H-point \[19, pg. 280\].

Olsen et al. and Jakobsson et al.\[18\] both reported that when the
stiffer vehicle side structures were involved in the rear impact the
rate of neck injury increased. In Jakobsson et al., it was also reported
that having a turned head at the time of impact increased the chance of
neck injury lasting more than three months. A reclined seat increased
the neck injury potential, but an extra cushion on the head restraint
did the opposite.

4.3 NASS Data for Front Outboard Occupants in Rear Impacts

The following analyses are based on NASS weighted data of towaway
crashes. Non-contact AIS 1 neck injuries (whiplash) to front outboard
occupants have been identified from impacts where the primary damage was
to the rear of the vehicle. As shown above in section 4.1, the majority
of whiplash injuries occur in non-towaway crashes. Therefore, the trends
found and observations made based on the towaway data may not hold for
the entire population of crashes.

4.3.1 Whiplash Rate by Head Restraint Type, Vehicle Type, and Occupant
Gender

Table 4.2 shows the annual number of whiplash injuries in rear impacts
to front outboard occupants over the age of fifteen from NASS weighted
data (1988 - 1994). The data are broken down by gender, vehicle type and
head restraint type. The parenthetical values in each cell are the rate
of injury. The injury rate for LTVs and PCs is 16.4 % and 29.8%,
respectively. This is consistent with the results reported by the agency
in 1989 using 1982 to 1984 NASS data \[32\]. The 1989 analysis included
LTVs without head restraints which were estimated to be 75% of the
total. The agency was not able to determine conclusively the reason for
the difference in whiplash injury rate.

For the 1988 to 1994 NASS data, only LTVs coded as having head
restraints were included. However, the LTV injury rate estimates may not
be as accurate as those for PCs because the LTV estimates are made from
a much smaller sample size. This is, in part, because LTVs were not
required to have head restraints until September 1, 1991. In the NASS
data file (1988 - 1994), more LTV seats were coded as not having a head
restraint than as having integral or adjustable, combined. Before the
1992 model year (MY), the way in which the NASS data collectors coded a
seat as having an integral or no head restraint was by subjective
assessment of seat appearance. No height measurement was made.
Therefore, seats which may have met the height requirement of FMVSS 202
were possibly coded as not having a head restraint.

Analyzing the PC results, the overall whiplash injury rate for both
sexes and restraint types is 29.8%. This is significantly less than the
rates of greater than 70% reported in Japanese insurance data \[27\] and
80% reported in a smaller Swedish study \[26\]. Part of this variation
may be due to whiplash not being mentioned in the accident reports
because of delayed onset. Also Kahane \[19, pg. 86\] showed from 1979
NASS data that the rate of whiplash or possible whiplash is higher for
non-towaway rear impacts than for towaway rear impacts. For the NASS PC
data the injury rate for females is slightly higher than for males, with
a difference of 1.4% (30.4 - 29.0) for the combined head restraint
types.

The difference in injury rate for restraint types is 3.3% (32.5 - 29.2),
with integral restraints having a higher rate for both sexes combined.
This is not consistent with the results from Kahane which indicated that
integral head restraints were more effective in reducing neck injury
\[19\]. It is not clear why these results differ. It may be that in
newer vehicles integral restraints are being placed in relatively
smaller vehicle than adjustable restraints in comparison to the vehicles
of the Kahane report (See Appendix E). Also, the designs of the
restraints may have changed over the years or occupants may be adjusting
them properly more often than in years past. Another reason for the
difference could be that Kahane used Texas data only and that data was
not limited to towaway crashes.

Table 4.2 NASS (1988-94) Avg. Annual Rear Impact Whiplash for Adult
Occupants (15+ yr.)

  -------------- -------------- -------------- -------------- --------------
                                Male           Female         M + F

  PC             Integral       5315 (31.3)†   6362 (33.5)    11,677 (32.5)

                 Adjustable     16,711 (28.4)  26,990 (29.7)  43,701 (29.2)

                 Int. + Adj.    22,026 (29.0)  33,352 (30.4)  55,378 (29.8)

                                                              

  LTV            Integral       775 (22.3)     359 (9.2)      1134 (15.4)

                 Adjustable     245 (15.0)     339 (22.8)     584 (18.7)

                 Int. + Adj.    1020 (20.0)    698 (13.0)     1718 (16.4)

                                                              

  PC + LTV                                                    57,096 (29.3)
  -------------- -------------- -------------- -------------- --------------

† Parenthetical values indicate injury rate.

4.3.2 Passenger Car Whiplash Rate by Occupant Height and Gender

The NASS data for PC rear impacts were sorted to determine the whiplash
injury rate by occupant height. The occupants were segmented into
categories having a three inch height range. Occupants of unknown height
were rejected, as were height ranges where the total number of
unweighted observations was less than 20. Figure 4.1 shows the
annualized total number of occupants involved in rear impacts and the
annualized number of occupants with whiplash. The median height range
for both the total number of involved occupants and occupants with
whiplash is 66 through 68 inches.

Kahane found that, for rear impacts, female occupants were more
vulnerable to neck injury (25% higher for towaway rear crashes) than
males, prior to FMVSS 202 being in place \[19, pg. 95\]. He theorized
that this was because females, on the average, have considerably
narrower necks and less muscle mass than males. Yet, the female neck
must support a head of roughly the same volume as the male neck. The
NASS data in Table 4.2 showed only a slightly higher female whiplash
rate ({30.4 - 29.0}/29.0 = 4.8%) for PCs when occupants of all heights
were lumped together.

Figure 4.2 shows the whiplash rate for each sex broken down by height.
Again, if the total number of unweighted observations was less than 20,
the data were not used. Each data point represents occupants with a
height range ±1.5 inches about this point. A line is plotted through
each data point using the "least squared" method. From these lines it
can be seen that the trend for the male data is increasing injury rate
with increasing height (slope = 0.01). The trend for the female data is
the opposite, but the line is flatter (slope = -0.005). A possible
explanation for these trends may be that since, on average, females are
shorter than males the current head restraint heights are more effective
in reducing injury for females. The taller males are not protected as
well, causing the steeper upward trend in injury rate. Looking at the
individual data points at the height ranges where the genders overlap,
females have a higher injury rate at two of three height ranges. This
may support the theory that female musculature is not as effective in
supporting the head.

4.3.3 Passenger Car Whiplash Rate by Occupant Age

An evaluation of rear impact whiplash rate by occupant age shows an
increase with age (Fig. 4.3). For occupants between 15 and 34 the rate
is 27.5 percent. For occupants between 35 and 54 the rate is 32.6
percent and for those 55 and over, 34.4 percent. This may be related to
the reduction in voluntary range of motion with increasing age (Table
3.2).

5.0 Review of ODI's Consumer Complaint File

The total number of consumer complaints related to head restraints for
model years 1988 - 1995 was 202 (Table 5.1). Twenty-two percent of the
complaints were related to the head restraint being too low/short for
the occupant. Twenty percent of the complaints were related to
visibility impairment.

Table 5.1 FMVSS No. 202 Complaints on Head Restraints, MY 1988-1995, all
models

  ----------------------------------------- -----------------------------
  Nature of Complaint                       Number of Complaints

  Too low/short                             45 (22.3%)

  Visibility impaired                       41 (20.3%)

  Does not stay up/locked                   30 (14.9%)

  No head restraints                        26 (12.9%)

  Poor design/location, no                  17 ( 8.4%)
  support/protection                        

  Uncomfortable, rattles, loose, other      17 ( 8.4%)
  minor problems                            

  Too far back                              13 ( 6.4%)

  Broke, failed                             13 ( 6.4%)

                                            202 (100%)
  ----------------------------------------- -----------------------------

Note: Results of data run performed on September 13, 1995

A subgroup of complaints (Table 5.2) was compiled to evaluate accident
related complaints with respect to head restraints. Five complaints
stated that the head restraint detached, bent or no longer locked due to
the accident. Four consumers believed they were injured because their
head restraint was too low. One consumer believed his accident was due
to impaired vision caused by the head restraint.

Table 5.2 Complaints Related to an Accident, MY 1988-1988, all Models

+---------------------------------------+------------------------------+
| Nature of Complaint                   | Number of Complaints         |
+---------------------------------------+------------------------------+
| Failed after accident (e.g.,          | 5                            |
| detached,                             |                              |
|                                       |                              |
| does not lock, bent, etc.)            |                              |
+---------------------------------------+------------------------------+
| Injured due to low head restraint     | 4                            |
+---------------------------------------+------------------------------+
| Injured due to no head restraint      | 4                            |
+---------------------------------------+------------------------------+
| Head restraint not up/locked          | 1                            |
|                                       |                              |
| during accident                       |                              |
+---------------------------------------+------------------------------+
| Impaired visibility caused accident   | 1                            |
+---------------------------------------+------------------------------+
|                                       | 14                           |
+---------------------------------------+------------------------------+

In the past, there were two investigations related to head restraints:
(1) Electrically Operated Headrest Failure or Malfunction\--BMW 5- &
7-series, MY unknown; and (2) Failure of Front Seat Head
Restraint\--Ford Taurus, MY 1986-1988. The first investigation was
initiated because the electrically operated front seat head restraints
could fail to move even though the drive motor was operating. The second
investigation was prompted because a consumer alleged that the
adjustable front seat head restraint could not be maintained in a raised
position. Neither of the investigations led to a recall.

6.0 Survey of Restraint Positioning and Fleet Composition

6.1 Occupant/Head Restraint Position Survey Results

In the Fall of 1995 a survey was performed at the Department of
Transportation Headquarters and a Washington area Metro (subway) parking
lot exit to evaluate head restraint usage. The survey included an
evaluation of the head restraint location relative to the drivers of PCs
and LTVs . The survey was aimed towards newer vehicles. The survey data
form is shown in Appendix C. The numerical results are given in Tables
6.1 - 6.4 and Figure 6.1. Two-hundred and eighty-two driver head
restraints were evaluated. There were two occurrences of restraint
removal. Seventy-seven percent of the surveyed restraints were
adjustable and 23 percent were integral (Table 6.1).

Table 6.1 Distribution of Integral and Adjustable Head Restraint

  ----------------------- ----------------------- -----------------------
  Sample Size             \% Integral             \% Adjustable

  282                     23                      77
  ----------------------- ----------------------- -----------------------

It was determined visually if the top of the head restraint was at or
above the level of the top of the driver's ear (Table 6.2). This is the
approximate location of the head's C.G. Fifty-nine percent of the
adjustable restraints surveyed were at or above the top of the driver's
ear. Seventy-seven percent of the integral restraints surveyed were at
or above the top of the driver's ear.

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.

![](media/image7.wmf)

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]{.underline}, \[6\]. 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 Back of Head Form to
                          of Head Restraint       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?

References

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2.  [Automotive News]{.underline}: Vol. 1, April 24, 1996, pp. 145.

3.  Barancik, J. I.; Anand, A. K.; Thode, Jr. H. C.; Kramer, C. F.;
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4.  Buck, C.A.; Dameron, F.B.; Dow, M.J.; and Skowlund, H.B. (1959):
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5.  Blincoe, L.H. (1994): The Economic Cost of Motor Vehicle
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7.  Ewing, C.L.; Thomas, D.J. (1972): Human Head and Neck Response to
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8.  [Federal Register]{.underline}, Vol. 31, July 15, 1966, p. 9637.

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10. [Federal Register]{.underline}, Vol. 39, March 19, 1974, p. 10268.

11. [Federal Register]{.underline}, Vol. 43, March 16, 1978, p. 11100.

12. [Federal Register]{.underline}, Vol. 44, April 26, 1979, p. 24591.

13. [Federal Register]{.underline}, Vol. 53, December 13, 1988, p.
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14. [Federal Register]{.underline}, Vol. 54, September 25, 1989, p.
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15. [Federal Register]{.underline}, Vol. , 1996

16. Foust, D.R.; Chaffin, D.B.; Snyder, R.G.; Baum, J.K. (1973):
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17. Foret-Bruno, J.Y.; Dauvilliers, F.; Tarriere, C. (1991): Influence
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18. Jakobsson, L.; Norin, H.; Jernstrom, C.; Svensson, S.E.; Johnsen,
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19. Kahane, D.J. (1982): An Evaluation of Head Restraint - Federal Motor
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20. Matsushita, T. et al. X-Ray Study of the Human Neck Motion Due to
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21. McConnell, W.E.; Howard, R.P.; Guzman, H.M.; Bomar, J.B.; Raddin,
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22. Mertz, H. J.; Patrick, L. M. (1967): Investigation of the Kinematics
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23. Mertz, H. J.; Patrick, L. M. (1971): Strength and Response of the
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24. Nilson, G.; Svensson, M.Y.; Lovsund, P.; Viano, D.C. (1994):
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    Univ., Gotegorg, Sweden, ISBN 91-7197-031-2.

25. Nygren, A.; Gustafsson, H.; Tingvall, C. (1985): Effects of
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    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
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    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
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28. Rachmilevitch, A. (1996): Anti-Whiplash Protection. Proc. 29th Int.
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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]{.underline}: Vol. 175, April, 1995, pp. 76.

Appendix A

Samples of Head Restraint Designs

![](media/image8.png){width="2.9972222222222222in"
height="2.9805555555555556in"}

![](media/image9.png){width="2.997916666666667in"
height="1.7708333333333333in"}

![](media/image10.png){width="2.9965277777777777in"
height="2.807638888888889in"}

Appendix B![](media/image11.png){width="2.998611111111111in"
height="2.1166666666666667in"}

Medical College of Wisconsin Test Setup

![](media/image12.png){width="5.997916666666667in"
height="5.001388888888889in"}

Appendix C

Occupant/Head Restraint Position Survey Form

NHTSA

HEAD RESTRAINT EVALUATION

**DATA SHEET**

+-----------+----------------------------+----------------------------+
| RESTRAINT | **ADJUSTABLE** **FIXED**   | **ADJUSTABLE** **FIXED**   |
| TYPE      |                            |                            |
+-----------+----------------------------+----------------------------+
| RESTRAINT | **TOP OF REST LEVEL WITH   | **TOP OF REST LEVEL WITH   |
|           | TOP EAR?**                 | TOP EAR?**                 |
| LOCATION  |                            |                            |
|           | YES                        | YES                        |
| **V       |                            |                            |
| ERTICAL** | ABOVE BELOW                | ABOVE BELOW                |
|           |                            |                            |
|           | CAN'T TELL                 | CAN'T TELL                 |
+-----------+----------------------------+----------------------------+
| RESTRAINT | TOUCHING                   | TOUCHING                   |
|           |                            |                            |
| LOCATION  | **\<** 4\" AWAY **\>** 4\" | \< 4\" AWAY **\>** 4\"     |
|           | AWAY                       | AWAY                       |
| **HOR     |                            |                            |
| IZONTAL** | CAN'T TELL                 | CAN'T TELL                 |
+-----------+----------------------------+----------------------------+
| USAGE     | ADJUSTED?                  | ADJUSTED?                  |
|           |                            |                            |
|           | YES NO                     | YES NO                     |
+-----------+----------------------------+----------------------------+
| OVERALL   | ADEQUATE?                  | ADEQUATE?                  |
| RATING    |                            |                            |
|           | YES NO                     | YES NO                     |
+-----------+----------------------------+----------------------------+
| VEHICLE   | MAKE/MODEL:                | MAKE/MODEL:                |
| INFO/     |                            |                            |
| NOTES     | **PC VAN UTIL LT**         | **PC VAN UTIL LT**         |
+-----------+----------------------------+----------------------------+

Appendix D

Head Restraint Height Survey Results

<table style="width:100%;">
<colgroup>
<col style="width: 12%" />
<col style="width: 12%" />
<col style="width: 6%" />
<col style="width: 11%" />
<col style="width: 7%" />
<col style="width: 6%" />
<col style="width: 7%" />
<col style="width: 7%" />
<col style="width: 7%" />
<col style="width: 9%" />
<col style="width: 9%" />
</colgroup>
<thead>
<tr class="header">
<th rowspan="3">Make</th>
<th rowspan="3">Model</th>
<th rowspan="3">Model Year</th>
<th rowspan="3">VIN</th>
<th colspan="3">Restraint Type</th>
<th colspan="3">Front Restraint Heights</th>
<th>Head Restraint Width 2.5" Below Top</th>
</tr>
<tr class="odd">
<th rowspan="2">Integral</th>
<th colspan="2">Adjustable</th>
<th>Integral</th>
<th colspan="2">Adjustable</th>
<th></th>
</tr>
<tr class="header">
<th>Linear</th>
<th>Angular</th>
<th>Max.</th>
<th>Min.</th>
<th></th>
<th></th>
</tr>
</thead>
<tbody>
<tr class="odd">
<td>Pontiac</td>
<td>Sunfire (2 Dr.); Bucket</td>
<td>1995</td>
<td>1G2JB1246S7525177</td>
<td></td>
<td>√</td>
<td></td>
<td></td>
<td>30.00"</td>
<td>28.38"</td>
<td>9.0"</td>
</tr>
<tr class="even">
<td>Jeep</td>
<td>Cherokee 4x4 (2 Dr.); Bucket</td>
<td>1994</td>
<td>1J4FJ27S5RL204793</td>
<td></td>
<td>√</td>
<td></td>
<td></td>
<td>28.5"</td>
<td>26.75"</td>
<td>10.75"</td>
</tr>
<tr class="odd">
<td>Ford</td>
<td>Windstar Minivan; Bucket</td>
<td>1995</td>
<td>2FMDA5142SBB41033</td>
<td>√</td>
<td></td>
<td></td>
<td>27.75"</td>
<td></td>
<td></td>
<td>9.75"</td>
</tr>
<tr class="even">
<td>Plymouth</td>
<td>Acclaim (4 Dr.); Split bench</td>
<td>1992</td>
<td>1P3XA46K1NF229044</td>
<td></td>
<td>√</td>
<td></td>
<td></td>
<td>28.25"</td>
<td>25.5"</td>
<td>11.5"</td>
</tr>
<tr class="odd">
<td>Saturn</td>
<td><p>SC Coupe</p>
<p>(2 Dr.); Bucket</p></td>
<td>1992</td>
<td>1G8ZG1475NZ113598</td>
<td></td>
<td>√</td>
<td></td>
<td></td>
<td>28.63"</td>
<td>27.0"</td>
<td>10.75"</td>
</tr>
<tr class="even">
<td>Eagle</td>
<td>Vision (4 Dr.); Bucket</td>
<td>1993</td>
<td>2E3ED56T9PH534039</td>
<td></td>
<td>√</td>
<td></td>
<td></td>
<td>27.5"</td>
<td>24.0"</td>
<td>10.25"</td>
</tr>
<tr class="odd">
<td>Nissan</td>
<td>240SX (2 Dr.); Bucket</td>
<td>1994</td>
<td>JN1AS44D4SW007796</td>
<td></td>
<td>√</td>
<td></td>
<td></td>
<td>29.13"</td>
<td>28.25"</td>
<td>9.25"</td>
</tr>
<tr class="even">
<td>Ford</td>
<td>Explorer (2 Dr.); Bucket</td>
<td>1993</td>
<td>1FMDU32XXPA55250</td>
<td>√</td>
<td></td>
<td></td>
<td>27.5"</td>
<td></td>
<td></td>
<td>14.25"</td>
</tr>
<tr class="odd">
<td>Chevrolet</td>
<td>Lumina (4 Dr.); Split bench</td>
<td>1995</td>
<td>2G1WL52MXS1172244</td>
<td></td>
<td>√</td>
<td></td>
<td></td>
<td>29.5"</td>
<td>27.0"</td>
<td>11.0"</td>
</tr>
<tr class="even">
<td>Honda</td>
<td>Civic (2 Dr.); Bucket</td>
<td>1993</td>
<td>2HGEH2367DH518401</td>
<td>√</td>
<td></td>
<td></td>
<td>29.25"</td>
<td></td>
<td></td>
<td>8.5"</td>
</tr>
<tr class="odd">
<td>Volvo</td>
<td>850 (4 Dr.); Bucket</td>
<td>1996</td>
<td>YV1LS556T2268222</td>
<td>√</td>
<td></td>
<td></td>
<td>31.25"</td>
<td></td>
<td></td>
<td>9.5"</td>
</tr>
<tr class="even">
<td>Toyota</td>
<td>Camry LE (4 Dr.); Bucket</td>
<td>1996</td>
<td>4T1BG12KXTU674917</td>
<td></td>
<td>√</td>
<td></td>
<td></td>
<td>29.5"</td>
<td>27.0"</td>
<td>11.25"</td>
</tr>
<tr class="odd">
<td>Ford</td>
<td>Taurus LX (4 Dr.);Bucket</td>
<td>1996</td>
<td>1FALP53S8TA118031</td>
<td></td>
<td>√</td>
<td></td>
<td></td>
<td>29.25"</td>
<td>27.75"</td>
<td>10.5"</td>
</tr>
<tr class="even">
<td>Honda</td>
<td>Passport (4 Dr.); Bucket</td>
<td>1995</td>
<td>4S6CY58V8S4416752</td>
<td></td>
<td>√</td>
<td></td>
<td></td>
<td>29.0"</td>
<td>27.5"</td>
<td>10.25"</td>
</tr>
<tr class="odd">
<td>Pontiac</td>
<td>Bonneville SE (4 Dr.); Split Bench</td>
<td>1996</td>
<td>1G2HX52K5TH200537</td>
<td></td>
<td>√</td>
<td></td>
<td></td>
<td>28.5"</td>
<td>26.25"</td>
<td>12.5"</td>
</tr>
<tr class="even">
<td>Ford</td>
<td>Probe SE (2 Dr.); Bucket</td>
<td>1995</td>
<td>1ZVLT20A0S5143817</td>
<td>√</td>
<td></td>
<td></td>
<td>29.0"</td>
<td></td>
<td></td>
<td>9.25"</td>
</tr>
<tr class="odd">
<td>Ford</td>
<td>Thunderbird (2 Dr.); Bucket</td>
<td>1995</td>
<td>1FALP6247SH130959</td>
<td></td>
<td>√</td>
<td></td>
<td></td>
<td>28.0"</td>
<td>26.25"</td>
<td>11.0"</td>
</tr>
<tr class="even">
<td>Ford</td>
<td>F-150 XLT P/U; Bench</td>
<td>1995</td>
<td>1FTEF15N6SLB25102</td>
<td></td>
<td>√</td>
<td></td>
<td></td>
<td>29.0"</td>
<td>27.0"</td>
<td>10.5"</td>
</tr>
<tr class="odd">
<td>Chrysler</td>
<td>Cirrus Lxi (4 Dr.); Bucket</td>
<td>1996</td>
<td>1C3EJ56H7TN124484</td>
<td></td>
<td>√</td>
<td></td>
<td></td>
<td>30.0"</td>
<td>27.25"</td>
<td>10.5"</td>
</tr>
<tr class="even">
<td>Dodge</td>
<td>Grand Caravan SE; Bucket</td>
<td>1996</td>
<td>1B4GP44R1TB185367</td>
<td>√</td>
<td></td>
<td></td>
<td>30.25"</td>
<td></td>
<td></td>
<td>10.25"</td>
</tr>
</tbody>
</table>

Appendix E

1995 Vehicle Sales Data and Restraint Type

  ---------------- -------- -------- ------------------- -------- --------
  Passenger Cars                     Light Trucks and             
                                     Vans                         

  Vehicle          95 Sales HR Type  Vehicle             95 Sales HR Type

  Ford Taurus      366266   A - 96\' Ford F pickup       691452   I

  Honda Accord     341384   A        Chevrolet C/K       536901   A
                                     pickup                       

  Toyota Camry     328602   A        Ford Explorer       395227   I - 96\'

  Honda Civic      289435   I        Ford Ranger         309085   I

  Saturn           285674   A        Dodge Ram pickup    271501   I

  Ford Escort      285570   A        Dodge Caravan       264937   I

  Dodge Neon       240189   I        Jeep Grand Cherokee 252186   I

  Pontiac Grand Am 234226   A        Ford Windstar       222147   A

  Chevrolet Lumina 214595   A        Chevrolet Blazer    214661   A

  Toyota Corolla   213640   A        Chevrolet S10       207193   I
                                     pickup                       

  Chevrolet        199001   A        Plymouth Voyager    178327   I
  Cavalier                                                        

  Chev. Corsica    192361   A        GMC Sierra pickup   176957   A

  Ford Contour     174214   A        Ford Econoline van  157803   I

  Nissan Altima    148171   A        Toyota compact      143472   A
                                     pickup                       

  Dodge Intrepid   147576   A        Nissan compact      126662   A
                                     pickup                       

  Buick LeSabre    141410   A        Chevrolet Astro     119510   I

  Ford Mustang     136962   A        Dodge Dakota        111677   I

  Nissan Sentra    134691   A        Jeep Cherokee       110552   I - 96\'

  Pontiac Grand    131747   A        Ford Aerostar       87547    I
  Prix                                                            

  Olds. Cutlass    128860   A        Chevrolet G van     86838    I
  Ciera                                                           
  ---------------- -------- -------- ------------------- -------- --------

Note: A = Adjustable, I = Integral. All sales data is for 1995. Head
restraint types are for MY 95 except as indicated.

Appendix F

Advanced Head Restraint Design

![](media/image13.png){width="4.997222222222222in"
height="3.439583333333333in"}

![](media/image14.png){width="5.996527777777778in" height="4.8125in"}

![](media/image15.png){width="5.795833333333333in"
height="3.436111111111111in"}