|FMVSS NO. 202|
PRELIMINARY ECONOMIC ASSESSMENT
AND REGULATORY FLEXIBILITY ANALYSIS
FMVSS NO. 202
HEAD RESTRAINTS FOR
Office of Regulatory Analysis and Evaluation
Plans and Policy
This Preliminary Economic Assessment accompanies a proposal to require front seat head restraints in passenger cars, pickups, vans, and utility vehicles to be capable of achieving a height where the top of the head restraint is least 800 mm (31.5 inches) above the H-point (which represents the normally seated 50th male hip point). The proposal would also add a lower limit on height; all required head restraints may not be less than 750 mm (29.5 inches) from the H-point. The proposal would require rear outboard head restraints. The proposal also would require that the distance between the back of the head form representing the position of a 50th percentile head, in a normally seated position, and the head restraint (defined as backset) be no farther than 50 mm (2 inches) in any adjustment position.
The benefits of increasing the height of head restraints are estimated to be:
9,575 whiplash injuries reduced in the front seat
4,672 whiplash injuries reduced in the rear seat
14,247 total whiplash injuries reduced
The agency does not have data to support an estimate of the benefits of the backset requirements.
Average costs per vehicle are estimated to be:
$4.21 in front seats
$3.61 in rear seats for vehicles with rear head restraints
$12.34 in rear seats for vehicles with no rear head restraints
$10.32 per average vehicle
Total cost per year is estimated to be $160.5 million ($65.5 million for the front seat and $95.0 million for the rear seat).
Based on the benefits from increasing head restraint height, and an estimate cost of $6,485 per whiplash injury, the cost per equivalent life saved is:
$3.0 million in front seats
$9.0 million in rear seats
$5.0 million total
Table of Contents
|I - Introduction|
|II - Background|
|III - The Proposed Rule|
|Alteration of the Dynamic Sled|
|Test Compliance Option|
|Positive Lock Requirement|
|Harmonization with all other Aspects of ECE 25|
|Head Restraint Height|
|Distribution of Head Restraints|
|The Safety Problem|
|Whiplash Injury Costs|
|VII Cost Effectiveness|
|VIII Regulatory Flexibility and Unfunded Mandate Acts|
|IX Costs and Benefits of Head Restraints in Center Seating Positions|
|Cost per Equivalent Fatality|
There are an estimated 272,088 whiplash injuries per year occurring in police-reported and unreported rear impact crashes. Many of these rear impact crashes are at low speeds.
It is the consensus of the biomedical community that whiplash injuries, due to rear impact crashes, occur as a result of the movement of the head and neck relative to the torso. Minimum height requirements are based on the premise that in the case of no head restraint, both the bending moment on the neck and the head rotational angle are maximized, resulting in cervical hyper extension. The height requirements are intended to prevent whiplash injuries by requiring that head restraints be high enough to limit the movement of the head and neck.
It is widely believed that reducing the gap between the occupant's head and the head restraint should reduce the movement of the head relative to the torso, and thus result in lower whiplash rates.
This proposed rulemaking would upgrade Federal Motor Vehicle Safety Standard (FMVSS) 202, "Head Restraints", by requiring head restraints to be higher, closer to the head, and be available in front and rear outboard positions. This proposal would harmonize many parts, but not all of FMVSS 202 with the Economic Commission for Europe Regulation No. 25 (ECE 25) - Uniform Provisions Concerning the Approval of Head Restraints (Head Rests), Whether or Not Incorporated in Vehicle Seats.) ECE 25 became effective beginning with newly introduced models approved after January 15, 1999, and all other vehicles 48 months later.
Since January 1, 1969, passenger cars have been required by FMVSS 202 to have head restraints in the front outboard seating positions. FMVSS 202 also applies to light trucks manufactured after August 31, 1991. The standard requires that either of two conditions be met:
The head restraint evaluation (1) performed by NHTSA in 1982 on passenger cars found that the effectiveness of integral restraints was 17 percent in reducing rear impact injuries, while adjustable head restraints were 10 percent effective in reducing rear impact injuries. An integral head restraint consists of a seat back high enough to meet the 27.5 inch height requirement. An adjustable head restraint 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. The difference in effectiveness may have been due in part to adjustable restraints not being as high as integral restraints when in their lowest position and not being properly positioned.
While the 1982 evaluation estimated the benefits of any injury in a rear impact, for the most part, head restraints are designed to reduce whiplash injuries. Page 86 of the same evaluation provides data which can be used to estimate the benefit of head restraints for just whiplash injuries. The data in the 1979 NASS data file were used because the effectiveness statistics were calculated using that data. There is no more recent statistics on effectiveness available. Combining non-towaways and towaways, whiplash injuries were the only injury in 60 percent of the cases. Thus, the effectiveness of head restraints in reducing whiplash injuries can be estimated to be 28.3 percent (17/0.6) for integral restraints and 16.7 percent (10/0.6) for adjustable restraints. This assumes that head restraints are only effective in reducing whiplash injuries.
In 1996, in order to help identify and examine issues related to the biomechanics of neck injuries, whiplash rates, occupant and head restraint positioning, and the state of contemporary and future head restraint designs, NHTSA issued a technical report for comments entitled, "Head Restraints - Identification of Issues Relevant to Regulation Design and Effectiveness." There were ten commenters to the technical report. The responses were mainly focused on three main issues, 1) rescission of dynamic test requirement, 2) clarification of test procedure, and, 3) proposal for testing consolidation . As part of the agency's Regulatory Reinvention Initiative, the agency discussed eliminating the alternative that limits rearward displacement of the head restraint to less than 45 degrees during a forward acceleration of at least 8g applied to the seat supporting structure because this alternative is cumbersome and has been rarely used.
The vehicle manufacturers supported eliminating the dynamic test requirement of FMVSS 202 as discussed in the technical report. Other respondents to the technical report did not agree that the dynamic test portion should be rescinded. The Liability Research Group believed that the dynamic test requirements of FMVSS No. 202 should be strengthened and not rescinded.
Atwood Mobile Products believed that the dynamic portion of the test requirements currently stated in FMVSS No. 202 depicted the real world more accurately and should not be eliminated. Also elimination of the test would place an undue burden by allowing only one test method.
Recreational Vehicle Industry Association (RVIA) believed that rescinding the dynamic portion of FMVSS No. 202 could limit the options available for testing and could place an undue burden on vehicle manufacturers by requiring the use of a single testing method.
RVIA stated that the dynamic testing option could be more representative of real world crashes involving rear impact than the more widely used static test provided in FMVSS No. 202.
IIHS stated that if FMVSS No 202 was amended as proposed in the technical report, only the geometric requirements would remain in the standard, and manufacturers would be deprived of the use of an alternative means of testing head restraints. IIHS "does not object in principle" to the effort to simplify FMVSS No. 202, but stated that the standard is one of the few standards where the U.S requirements are weaker than elsewhere.
Volvo, who was in favor of the elimination of the requirement, believed there was insufficient knowledge about injury mechanisms and that test dummies needed to be improved. However, Volvo has developed a seat design to specifically reduce whiplash injuries, indicating that they believe they have enough knowledge to change the way they design seats.
Chalmers University of Technology supported a dynamic test and believed it was a necessity for active head restraints. Active restraints are designed to deploy upon rear impact. A 1998 Saab model is equipped with an active restraint which operates by use of a lever. This type of system may not pass a static dimensional requirement in its undeployed state.
At that time, the agency was not aware that vehicle manufacturers such as these represented by the RVIA or by Atwood Mobile Products considered the alternative dynamic test of FMVSS No. 202 to be an engineering alternative because it had been rarely used. The agency believes that it was not the intention of the "Regulatory Reinvention Initiative' to restrict the choice of options available to manufacturers who wish to use them or to impose a hardship on manufacturers or to impede or stifle technical innovation. Based on these comments, the agency was and still is concerned that deleting the option could stifle future technological innovation in the area of deployable crash protection systems that provide head restraint during a crash. Therefore, based on the new information provided by RVIA, Atwood and IIHS, the agency decided that the dynamic test portion of FMVSS No. 202 should not be rescinded at that time because it offered manufacturers a convenient alternative to evaluating head restraint performance during vehicle manufacture and that this alternative may be used in the future.
In addition to the above reasons, the agency still wishes to retain the dynamic option because future designs which may use air bags, could be assessed. Looking to the future, the agency would ideally have a more performance based regulation for head restraints rather then the current design regulation. A more performance-based regulation provides the means to assess the many other seat design parameters which affect whiplash reduction. Research has shown that seat back stiffness, seat cushion stiffness, seat cushion contour and seat cover material can all affect neck loading. A dynamic test is the ideal way of combining aspects of the seat standard (FMVSS 207) and FMVSS 202. However, future rulemaking will be needed to deal with improving seat performance related to occupant injury in higher speed rear impacts. Advocates for Highway and Auto Safety supports the agency's exploration of a dynamic only head restraint regulation. The current dynamic option provides a stepping stone towards a purely performance based regulation.
III. THE PROPOSED RULE
The proposal would require that head restraints in all outboard seats, when adjusted to their lowest possible adjustment position, be higher (at least 750 mm or 29.5 inches) than they are currently required to be at their highest position (at least 700 mm or 27.5 inches). It would also require them to be able to achieve a greater height at their maximum height adjustment in front outboard seats (at least 800 mm (31.5 inches)), and lock positively in that position. Head restraints in front outboard seats would also be subject to a new requirement limiting the amount of backset to less than 50 mm (two inches) at any adjustment position. It also adds a requirement that head restraints be provided in the rear outboard seating positions. With the exception of the width requirement for head restraints on bench seats and the backset requirement, the amendments being proposed by NHTSA are the same as the requirements for head restraints in ECE Regulation No 25. The agency proposal would also modify the test procedures used for certifying compliance to Standard 202. Manufacturers would have the option of certifying compliance in one of two ways: the first option is a series of dimensional, strength and energy absorption requirements. The second option consists of a dynamic test with associated performance criteria and a static width requirement. With the second option, demonstrate compliance with the 50th percentile male Hybrid III test dummy specified in Part 572 Subpart E. For front seating positions demonstrate compliance with the 95th percentile male Hybrid test dummy specified in Part 572. When testing with the 95th percentile male Hybrid dummy demonstrate compliance with the head restraint at one position of height adjustment, at the option of the manufacturer. When testing with the 50th percentile demonstrate compliance with the head restraint at any position of height and backset adjustments.
Alteration of the dynamic sled test compliance option
Altering the height requirement will necessitate the modification of the dynamic compliance option in FMVSS 202. The current dynamic test accelerates a seat loaded with a 95th percentile adult male dummy to at least a 78.1 m/s2 (8g) half sine acceleration pulse over 80 ms. The dummy neck must not rotate rearward with respect to the torso more than 45 degrees. The 45 degree performance limit was developed such that a 700 mm (27.5") high restraint would pass the dynamic test. If left unaltered, manufacturers could pass the standard using the dynamic test with 700 mm (27.5") high restraints even though the new proposed height requirement is 800 mm (31.5").
To avoid this, the agency proposes to alter the performance requirements in the dynamic procedure such that head restraints of 750 mm (29.5") with a 50 mm (2.0") backset, could pass. Additionally, the way in which the sled pulse corridor is defined has been refined. Additionally, the way in which the acceleration pulse corridor is defined has been altered. Rather than being defined by two sinusoids, it is now a series of straight lines scaled down from the sled pulse corridor in FMVSS 208. In addition to the head rotation performance criterion, the HIC must remain below 200 during the acceleration test. The dynamic compliance option also requires a minimum head restraint width.
FMVSS 202 currently requires that all head restraints be capable of achieving a height where the top of the head restraint must be at least 700 mm (27.5 inches) above the seating reference point measured parallel to the torso reference line. The agency proposes to change this requirement to 800 mm (31.5 inches) above the H-point for front seat head restraints, and require a lower limit on both front and rear head restraints of not less than 750 mm (29.5 inches) above the H-point. The new requirements will result in integral front seat head restraints having a minimum height of 800 mm (31.5 inches); adjustable front seat head restraints would be capable of achieving a height of 800 mm (31.5 inches) and could not be adjusted lower than 750 mm (29.5 inches).
The proposed alteration in the height requirement is intended to prevent whiplash injuries by requiring that the head restraints be high enough to limit the rearward movement of the head and neck. Research conducted since the implementation of the current height requirements has shown that head restraints should be at least as high as the center of gravity (CG) of the occupant's head to adequately control motion of the head and neck relative to the torso. Assuming the simplified representation of a head restraint and occupant head in fig.1, a head restraint height of 750 mm (29.5 inches) would provide this height for a 50th percentile male until a backset of approximately 125 mm (5 inches) is reached. While a head restraint height of 700 mm (inches) will be above the C.G. of the 5th percentile female up to about 10 inches of backset.
The difference in average erect seating height between a 50th and 95th percentile male is 58 mm (2.3 inches). It is reasonable to assume that this difference is due to a longer torso between the H-point and base of the neck and that the dimensions from the base of the neck to the top of the head are nearly identical. A 95th percentile male will have the top and C.G. of the head 53 mm (2.1 inches) higher than the same points on a 50th percentile male. It is further assumed that the back of the 95th and 50th percentile male heads are in the same backset position relative to the head restraint. This is because the longer torso of the 95th percentile male would tend to place it closer to the head restraint and the larger lower back and buttocks would push the H-point away from the back of the seat, resulting in a zero sum gain of backset. Based on these assumptions, a 750 mm (29.5 inches) high head restraint would be as high as the 95th percentile male C.G. up to a backset of 13 mm (0.5 inches). A head restraint with a height of 800 mm (31.5 inches) would be as high as the 95th percentile male C.G. up to a backset of 133 mm (5.3 inches). Since backset is limited to 50 mm (2 inches) a seated occupant with a head C.G. approximately 38 mm (1.5 inches) higher than the 95th male would be covered by the proposal. This would mean that the proposed regulation would require head restraint heights sufficient to capture greater than 99 percent of the population.
There are several reasons why the agency is proposing to allow lower head restraints for the rear seat than for the front seat. First, the rear seats of many passenger cars are fixed and may result in lower injuries. The NASS data indicate a lower whiplash rate for rear seat occupants (see Table V-3). Second, the average height of rear seat occupants is less than front seat occupants. Third, visibility out the rear window was considered. The taller the rear head restraints, the less visibility is afforded to drivers out of the interior rearview mirror.
NHTSA is proposing to add a requirement that head restraints must have a backset of less than 50 mm (2 inches), at any adjustment position. (see Figure 1 in Chapter V for a visual depiction of backset). As proposed by the agency, backset would be measured at any point between a height of 750 mm and 800 mm. The consensus of the biomechanics community is that the backset dimension has an important influence on the forces felt by the neck and the length of time a person is disabled by injury. This has been based on both physical tests, computer modeling and real world crash data. Research seems to indicate 100 mm (four inches) as the upper limit of acceptable backset. Some researchers have seen further potential injury reduction as the backset goes to zero, allowing no relative motion between the head and torso upon rear impact.
In general, the NHTSA computer modeling results using a 50th Hybrid III dummy can be summarized in the following way. The lowest relative head rotation value was seen for the head restraint height positions between 750 and 800 mm, with a backset of about 0". Backset increased by an average of 2.2 inches when backset was increased to 50 mm. The average head rotation change was 19.8 degrees when going from 50 mm to 100 mm backset. Therefore, NHTSA believes that a head restraint which can achieve this position would be best.
Adjustment Retention Requirement
Adjustable restraints are most often criticized because they are not positioned properly by motorists and they do not lock in position. Most commentors to the Technical Report were in favor of positive locks on adjustable head restraints. The benefit of the locking requirement is to keep the head restraint in the adjusted position. The agency believes that if the head restraint can be pushed down or back by the head during the crash sequence, there is a higher likelihood of injury to the occupant.
The modification to the existing height requirements and the addition of a backset requirement that are now being proposed are expected to improve the performance of all adjustable head restraints. The performance of adjustable head restraints may be further improved if steps are taken to ensure that restraints remain in position after they have been set by the user. It is proposed that adjustable head restraints for the front outboard seating positions must lock in several height positions under application of a downward force. In addition to locking a height position of not less than 800 mm (31.5 inches), they must lock at the highest and middle height adjustment positions.
The agency has tentatively concluded that a lock requirement for other positions within the range of adjustable is unnecessary. Requiring additional locking mechanisms to hold the restraint in an intermediate position within this two inch range of adjustment of height would not, in NHTSA's view, result in additional safety benefits commensurate with the cost. The agency notes, however, that manufacturers would not be precluded from using locking mechanisms that operate within the range of the head restraint's vertical adjustment.
This NPRM proposes performance requirements which are intended to assure that the head restraint, if adjustable, will remain locked in specific backset and height positions. The agency believes that this important for designs which adjust vertically as well as rotate for backset adjustment. The requirement for horizontal locking is located in S4.3(b)(11) and is tested as part of S5.6. The requirements are written such that a front seat restraint must be placed in a height position closest to but greater than 800 mm (31.5 inches) and the backset position closest to 50 mm (2 inches). Rear head restraints must be in a height position closest to but not less than 750 mm (29.5 inches). Positive locking of the head restraint is not required in other adjustment positions, but is not forbidden. The tests are written such that an initial small load is applied to the head restraint and the reference position of the loading device (head form) is recorded. The head form reference position is measured with this load applied to eliminate positioning variability associated with the soft upholstery of the head restraint. A larger load of 500 N (56.2 lbs) for vertical loading and a load sufficient to generate a 373 Nm (3,300 inch lb) moment for rearward loading is then applied to test the locking mechanism. Finally, the load is then reduced back to the initial value and the head form is checked against its initial position. It must be within 10 mm (0.36")of its initial position to pass. The test was designed assuming, if the locking mechanism fails, the head form would not return to its original position.
The process of global harmonization in the field of vehicle regulatory requirements began in 1949. The Geneva Convention on Road Traffic and Signs was created by the United Nations Economic Commission for Europe to examine the problem of vehicle movement across countries. This convention formally permitted the temporary passage of road vehicles from one country to another without meeting national vehicle construction and use regulatory requirements, so long as a list of minimum specific requirements was met. Since then, most countries around the world have become signatories to it.
It is the opinion of many that global harmonization would eliminate the barriers to trade resulting from unwarranted differences in vehicle regulations and certification and compliance procedures. Compliance with multiple regulatory frameworks reduces vehicle affordability as it imposes substantial cost due to design and manufacturing constraints. These constraints extend the time needed to develop new products, thus preventing manufacturers from responding quickly to the needs of consumers world-wide. The agency favors harmonization as long as safety is improved or the safety effects are neutral.
Harmonization with all other aspects of ECE 25
In addition to the height and rear seat requirements, harmonization with ECE 25 would entail adding maximum gap dimensions (a gap is defined as either see-through holes in the head restraint or the distance between the top of the seat and the bottom of an adjustable head restraint) and energy absorption requirements to FMVSS 202. Harmonization would also require reducing the head restraint width for bench seats from 10" to 6.7". Since most head restraints probably meet the gap and energy absorption criteria in ECE 25, putting these requirements in FMVSS 202 should not add significantly to safety or to cost.
NHTSA believes that the final rule should not incorporate the portion of ECE 25 which would allow a 6.7" wide restraint on bench seats rather than the 10" required by FMVSS 202 because this may degrade the level of safety currently available. Based on the length of bench seats, occupants seated on bench seats compared to occupants of single seats are freer to position themselves such that they are not directly in front of the head restraint. This is especially true if they don't use their safety belts. Thus, the wider the head restraint, the more likely it will provide benefits to occupants.
In order to eliminate head restraint designs that have gaps so large that they would detract from the safety aspects of the head restraints, this proposed rule establishes maximum gap requirements similar to ECE 25. For fixed designs, ECE 25 allows a maximum 60 mm (2.36") gap in the head restraint. This is to prevent the head from getting too far into the gap in the head restraint. The gaps in the head restraint may be used for visibility. For height adjustable restraints, 60 mm (2.36") gaps are allowed in the head restraint and a 25 mm (0.98") gap is allowed between the head restraint and seat. The agency is not aware of the exact rationale used by the Europeans in developing the specific gap limits. Nonetheless, in the absence of independent test data the gap requirements in the proposed regulation are, with one exception, identical to the ECE 25 specifications. This exception is for the gap requirement between the head restraint and seat, when the seat is in the lowest position. The ECE requirement does not contemplate back set adjustability and simply allows no more than a 25 mm (0.98 inch) gap. However, for the proposed regulation, this gap cannot be greater than 60 mm (2.36 inches) in any position of backset adjustment.
The agency is proposing that adjustable restraints in their lowest height position have some position of adjustment where the gap between the seat and head restraint is less than 25 mm. There can be no position of adjustment where this gap is greater than 60 mm. The agency requests comments on the need for the 25 mm gap and whether it could be increased.
c. Energy Absorption
This proposal would require an energy absorption requirement similar to ECE 25. The impact procedure used by ECE 25 to determine energy absorption is consistent with that previously used for the back of the seat in FMVSS 201 and 222. The impactor may be a free-flying head form or a pendulum. The impactor would be used to strike the front of the head restraint. The agency has no knowledge of occupant head-to-head restraint contact being a source of injury. However, if a head restraint were too hard, head injury could occur. The agency also believes that most, if not all head restraints, would be in compliance. Therefore, this requirement is added on the basis of increasing the level of harmonization with ECE 25, and directionally to prevent possible head impact injuries from striking a head restraint that was too rigid. The ECE 25 test procedure specifies that the head restraint be placed in the most unfavorable position. The proposed regulatory text requires the head restraint to pass in any position of adjustment. As in ECE 25, the injury criteria requires an acceleration of less than 785 m/g2 (80g) for more than 3 ms. Another difference between the proposed regulatory text and ECE 25 is the impact area. The ECE 25 standard limits this area to within 70 mm (2.76") of the head restraint centerline. The agency proposes this same limit for bucket seats, but increases the impact area to within 105 mm (4.13") of the centerline for bench type seats. This is done because in FMVSS 202 bench type seats must have wider head restraints then single seats. The proposed impact area covers the same percentage of the required head restraint width for both types of seats.
The agency believes that the requirement should include a minimum radius of curvature for the front surface of the head restraint that matches ECE 25. Any part of the head restraint outside of the impact zone for the energy absorption requirement must not have a radius smaller than 5 mm (0.2") unless it can pass the energy absorption requirement. This requirement does not allow sharp edges on the head restraint and it avoids high pressure points that could injure someone and still pass the 80 g criterion. NHTSA has no knowledge that small radius surfaces exist on current restraint designs and believes that most, if not all head restraints, would be in compliance.
d. Head Restraint Displacement Test Procedure
The agency proposes altering the head restraint displacement test procedure so that it matches the test in ECE 25. The genesis for this change was a petition for functional equivalence from AAMA/AIAM indicating that they believed that the ECE 25 test procedure for head restraint deflection was more severe that the FMVSS 202 procedure.
The difference in the two test procedures is the back pan load. In FMVSS 202 the back pan load is removed before application of the moment to the head restraint and in ECE 25 the back pan position is maintained while the head restraint moment is applied.
Depending on the stiffness of the seat in the ECE test, the back pan load will decrease as increasing load is applied to the head restraint. AAMA/AIAM provided data from one 1998 model year vehicle seat that showed a 64 mm (2.5 in.) displacement for the US method and a 89 mm (3.5 in.) displacement for the ECE method. Although this may not be representative of the difference in displacement which is likely to occur in most seats, AAMA/AIAM believed that in all cases the displacement measured by the ECE procedure will be equal to or greater than the US procedure.
The agency has reviewed this information and believes the data provided by AAMA/AIAM to be reasonable. Because the back pan position is maintained in the ECE procedure, some level of load may be applied through it to the seat. This load, along with the load applied to the head restraint, result in the total applied seat moment and contribute to head restraint deflection. Thus, the head restraint deflection may be greater if the back pan not is removed before application of the head restraint load. The agency believes that applying loads to both the back pan and the head restraint simultaneously better reflects the stresses that occur in rear end crashes. This change in the test procedure will result in safer performance and is closer to a real world situation.
Finally, the existing displacement procedure allows the seat back to fail without consequence under application of 890 N (200 lbs) to the head restraint. Yet, the requirement specifies that the head restraint must "withstand" this load. NHTSA believes that allowing the seat back to fail renders this requirement unenforceable. Therefore, the NPRM removes the allowance for seat back failure.
A common consumer complaint about head restraints is that they reduce visibility to the rear of the vehicle. There are two areas of concern. The first is the driver's head restraint. When the driver has the vehicle in reverse and turns his/her head to see behind the vehicle, a properly positioned head restraint may be in the line of sight of the driver, forcing the driver to lean to the side to see around the head restraint or to straighten up to see over the head restraint. (Some head restraints have openings, but looking through these relatively narrow gaps does not seem to be a preferred way of backing up). The majority of drivers would not be affected by the proposed head restraint height increase because the line of sight of a 50th percentile male is approximately 690 mm, which is below the 700 mm head restraint height currently required. Therefore, at least 50 percent of the male driving population and over 50 percent of the female drivers have to lean around current head restraints to look rearward. An increase in the head restraint height requirement will not adversely effect these drivers. Head restraints with a minimum height of 750 mm (29.5 inches) will cause a much higher percentage of drivers (many of those 47 percent of current drivers that leave their head restraint in the lowest position) to straighten up or to lean to the side to see around the head restraint. The physical difficulty of straightening up or leaning to the side while looking backwards depends upon the flexibility of the driver. Those drivers with neck, shoulder, or back problems, and some elderly drivers, may find it difficult or painful to straighten up or lean to the side and look back. Drivers could use the exterior mirror systems on the vehicle to back up, but that does not seem to be the preference of drivers.
The second area of concern is how rear seat head restraints reduce the direct visibility of the driver when looking backward and the indirect visibility of the driver when looking through the inside rearview mirror. The agency is not proposing that head restraints be installed in the center seating position of the front or rear seats. These positions would be even less cost effective than the rear outboard seating positions and they further reduce rear visibility. The agency is proposing that the rear seat head restraints need not be able to be raised as tall as the front seat head restraints. There are several vehicle models already on the road with head restraints that meet the proposed rear seat height requirements. The agency requests comments on whether there are problems with these models. An informal survey of NHTSA employees of different heights was performed in a MY 1999 Toyota Camry, which meets the rear seat height proposal. The rear seat head restraints were adjusted to their highest point. The findings of the survey were that drivers could still see well to the rear of the vehicle over the top of the raised head restraints, but the head restraints do reduce visibility. However, this is just one model and there may be large differences in the vision blockages caused by rear head restraints. Again, drivers could use the exterior mirror systems on the vehicle to observe following traffic. However, there may be blind spots using the exterior mirror that could have been seen by the driver using the interior rear view mirror that may now be blocked by the rear seat head restraint. Rear head restraints could cause a change in driver behavior, forcing them to use exterior mirrors more or to be even more cautious and turn their head to the side to check for vehicles. For many drivers it is preferable to have as much visibility as possible to the rear of the vehicle using the interior rear view mirror. There are many potential visibility impacts and potential changes in driver behavior that could impact on lane change maneuvers. Their overall impact on crash avoidance is difficult to determine.
A study (2), by Mats Y. Svensson, Per Lovsund, Yngve Haland and Stefan Larson, presented at the 1993 International IRCOBI Conference on the Biomechanics of Impact, 8-10 September, Eindhoven, The Netherlands, on the Influence of Seat-Back and Head-Restraint Properties on the Head-Neck Motion during Rear-Impact found that backset had the largest influence on head-neck motion, with the maximum head-torso displacement increasing with increasing backset. The study also found that the increased stiffness of the seat-back frame resulted in slightly increased maximum head-torso displacement, but a stiffer lower seat-back cushion combined with a deeper upper seat-back cushion resulted in a clear reduction of the head-torso displacement.
A study (3) of 26 rear end crashes involving 33 front seat occupants in Volvo cars was made in Sweden during 1987-88. The study investigated neck injuries sustained in rear end crashes and correlated the severity of the injuries with the various crash, occupant, and vehicle parameters. All injuries in the study were of minor severity (AIS 1). Seventy percent of the occupants suffered neck injuries with symptoms localized in the neck only. The study found that there was a relation between an increase in backset and the severity and length of neck symptoms. That is, a distance of more than 10 cm between the head and the head restraint correlated with an increased risk of neck injuries in rear end collisions, and reducing the backward movement of the head in relation to the chest might be of primary importance.
A neck injury criterion (NIC) to mathematically model and predict neck injuries in low-speed rear-end automobile crashes has been proposed (4) based on the relative acceleration and velocity between the top and the bottom of the cervical spine. In the study none of the subjects' NIC values exceeded the previously proposed 15 m2/s2 threshold, yet overall 33 percent of the tests resulted in symptoms. Of the 42 subjects tested 22 (52%) reported symptoms at either 4 or 8 km/h speed change. One reason the NIC may not have predicted the occurrence of whiplash symptoms in the test subjects was because NIC is based on a pressure gradient injury mechanism model that predicts dorsal root ganglion pathology, while the precise source of the tested subjects' symptoms was not known. It was not possible to verify by histopathological examination whether or not dorsal root ganglia injury occurred to the test subjects. Furthermore, no significant differences were noted in post-impact clinical examinations for reflex, sensory, or upper extremity muscle strength, which suggested that the test subject symptoms were not nerve based. NIC was not able to predict the presence of symptoms in the test population. This study suggests that further refinement may be necessary for NIC.
Head Restraint Height in Vehicle Fleet
Table IV-1 presents data on the difference between the proposal and measurements of head restraint height and backset taken on 14 model year (MY) 1999 models at the highest adjusted height for the head restraint. For example, the MY 1999 Toyota Camry was measured and the driver's seat highest head restraint position was 30.75 inches or 0.75 inches lower than the proposed height of 800 mm (31.5 inches).
Sales weighted averages derived from these measurements are shown in the Tables IV-2, IV-3, and IV-4. They represent the differences between the measured heights and the proposed standard. Averages in the front seat are for the driver and right front passenger positions and in the rear seat are for the right and left rear passenger positions. Both the lowest height and highest height are used for calculations made in the safety benefit and cost sections of this assessment.
Measured at the Highest Head Restraint Height
Number of Inches Head Restraint Has to be Increased
and Backset Reduced to Meet Proposed Standard
31.5 Inches Front and 29.5 Inches Rear Height (Ht) and 2 Inch Backset (BS)
|Make||Driver||Right Front Pass.||Right Rear Pass.||Left Rear Pass.|
|Chevy C1500 /GMC||0.25||0||0.5||0||...||...||...||...|
|* These vehicles have adjustable rear seat head restraints. Some of the other vehicles have integral restraints which consist of a lump in the seat back that raises the height of the seat back.|
Note: Of the vehicles with adjustable head restraints:
In the front seat, 6 had positive locking mechanisms for height and 6 did not.
In the rear seat, 3 had positive locking mechanisms for height and 3 did not.
|Front Seat||Rear Seat|
|Integral Head Restraint||1.2||3.9|
|Adjustable Head Restraint||1.4||1.0|
|Front Seat||Rear Seat|
|Integral Head Restraint||NA||3.9|
|Adjustable Head Restraint||1.5||3.7|
|Front Seat||Rear Seat|
Distribution of Head Restraints
In the 1982 Evaluation of passenger car front seat head restraints, 62 percent were adjustable head restraints and 38 percent were integral. In the 1988 to 1996 NASS-CDS, which includes whatever model year of vehicle had head restraints, the mix was 77 percent adjustable and 23 percent integral for passenger cars. NHTSA found that in a sample of MY 1998 passenger cars representing 47 percent of passenger car sales, 93 percent were adjustable and only 7 percent were integral head restraints. Thus, there has been a significant trend towards adjustable head restraints in the front seat of passenger cars.
The distribution of adjustable and integral head restraints for light trucks is very different. In the 1988 to 1996 NASS-CDS, 23 percent of the front seat light truck head restraints were adjustable and 77 percent were integral. In a sample of MY 1998 light trucks representing 72 percent of light truck sales, a sales weighted distribution found 20 percent adjustable and 80 percent integral head restraints.
Sales-weighting cars and light trucks by calendar year 1998 sales results in 9.06 million vehicles (an average of 58 percent of the vehicles) having adjustable head restraints and 6.49 million (an average of 42 percent of the vehicles) having integral restraints (based on 8.15 million passenger cars and 7.40 million light trucks totaling 15.55 million vehicles). These estimates are close to the original passenger car distribution (62 adjustable and 38 integral) in the 1982 evaluation and thus the average effectiveness, regarding the distribution of adjustable and integral, from the 1982 evaluation can be used for this analysis. Although the injury rate of cars and light trucks are not identical, the agency is using the average effectiveness of passenger cars because there is no available effectiveness statistics on light trucks.
While the agency has some information on the distribution of head restraints in the rear seat, the information is not very complete. About half of the vehicles with rear seats have "head restraints" and half do not. However, some of the so called "head restraints" are far from the height being proposed and they may constitute just a lump at the top of the seat back. Whether the manufacturers would extend these into integral head restraints or change the design and add an adjustable head restraint is not known. It appears that most of the European passenger cars are using adjustable head restraints in the rear seat. Whether this is in consideration of visibility concerns through the inside rearview mirror or not, is not known.
The Safety Problem
NHTSA estimates from NASS data, that between 1988 and 1996, there were 805,851 occupants with whiplash injuries annually in the outboard seating positions of passenger cars, light trucks, and vans in towaway and non-towaway, police reported and unreported, nonrollover impacts. The average cost (excluding property damage) of such an injury is $6,485, resulting in a total annual cost of $5.2 billion. However, since the agency believes head restraints will be most effective in rear impacts, the benefits analysis will be restricted to this crash mode.
It is estimated from National Automotive Sampling System - Crashworthiness Data System (NASS-CDS) data that between 1988 and 1996, there were 70,307 occupants with whiplash injuries (non-contact AIS 1 neck injuries) annually in the outboard seating positions of passenger vehicles (5) in police-reported towaway nonrollover rear impacts (see Table V-1a). Whiplash injuries can occur at low speeds and many times the occupant doesn't know they have been injured for several hours. Thus, adjustments must be made to account for injuries in non-towaway police reported crashes and for crashes that are not reported to the police.
Data on non-towaway whiplash injuries are not available in the NASS-CDS data base since 1988. The agency examined data in two states, Pennsylvania (1997, State data file) and Indiana (1996, State data file) that had data elements on body region of injury and towaway versus non-towaway police reported crashes. In rear impacts in Pennsylvania, there were 2,840 outboard occupants in towaway crashes and 5,815 in non-towaway crashes with a whiplash injury (defined using Pennsylvania data as a neck injury, with no visible sign of injury but a complaint of pain.) Thus, the multiplier from police reported towaway injuries to total police reported injuries would be 3.05 [(5,815 + 2,840)/2,840]. In rear impacts in Indiana, there were 2,074 outboard occupants in police reported towaway crashes and 4,096 in police reported non-towaway crashes that had neck injuries, with a complaint of pain. Thus, the multiplier from police reported towaway injuries to total police reported injuries would be 2.97 [(4,096 + 2,074)/2,074]. There is no statistically significant difference between these two multipliers. On average, the multiplier from towaway injuries to total injuries is 3.0. Thus, we estimate the annual estimated number of police-reported whiplash injuries in rear crashes to be 210,921 (70,307 x 3).
Based on estimates provided in a NHTSA report (6), the multiplier from police-reported crashes to all crashes, including unreported crashes, for AIS 1 injuries is 1.29. Thus, the annual estimated number of total whiplash injuries in rear crashes, police- reported and unreported is
272,088 (210,921 x 1.29).
Out of the 70,307 estimated whiplash injuries in towaway crashes, an estimated 5,440 (7.7 percent) were in rear outboard seating positions. The annual estimated number of total whiplash injuries in rear outboard seating positions, police- reported and unreported is 21,053 (5,440 x 3 x 1.29). Of the 5,440 whiplash injuries in rear seats in towaway crashes, only 564 (10.4 percent) were in vehicles with head restraints in the rear seat. The number of vehicles with head restraints in the rear outboard seats has increased dramatically over the last several years. Based on the MY 1999 vehicles with rear seat head restraints and MY 1998 sales, an estimated 41 percent of the MY 1999 fleet have head restraints that were at least 750 mm (29.5 inches), 39 percent have a rear seat but no head restraints, and 20 percent have no rear seat. Out of the possible 80 percent of the fleet with a rear seat, 41 percent have a head restraint. Thus, 51 percent (41/80) of the possible rear seat injury cases for new models would now have a head restraint. Since the average effectiveness of rear head restraints is estimated to be about 14 percent (see discussion on page V-16), then the expected number of rear seat outboard whiplash injuries for a fleet of MY 1999 vehicles if they had no rear seat head restraints would be 21,429 based on the following calculations:
Potential Whiplash = AW/(1-ue)
where AW = actual whiplash
p = presence rate of head restraints
e = effectiveness
p represents the rate of head restraint presence in all crashes. It is derived from the presence rate in injury crashes, but must be adjusted to reflect those saved from injury by head restraints. This adjustment is made using the following formula:
Where e = effectiveness of head restraint and pi presence rate of head restraints among injured occupants
Thus p = .104/1-(.1467(1-.104)) = .1197
21,053/[1-(.1197 presence x .1467 effectiveness)] = 21,429 in potential whiplash cases
21,429 x .1467 x .51 = 1,603 whiplash injuries saved by MY 1999 head restraints
21,429 - 1,603 = 19,826 remaining rear seat outboard whiplash injuries
There is no need to make the same adjustment for front seat head restraints, since essentially all vehicles in the 1988-96 period already had front seat head restraints. Table V-1(b) provides the target population projected number of annual towaway whiplash injuries for a fleet of MY 1999 vehicles at their current rate of head restraint installation. There would be an estimated 251,035 (272,088 - 21,053) front outboard and 19,826 rear outboard whiplash injuries for a total of 270,861 occupants injured in towaway and non-towaway, reported and unreported rear crashes.
|Front Seat Outboard||Rear Seat Outboard||Total|
Distribution of Integral and Adjustable Head Restraints
Annualized NASS-CDS Data 1988 - 1996, Towaways
|Head Restraint Type When Known||Whiplash Injuries||Ratio|
The distribution of injuries by type of head restraint is in the ratio of 0.27 to 0.73 (Table V-2). The distribution of front seat outboard injuries by restraint type is:
Integral head restraint = .27 x 251,035 = 67,779
Adjustable head restraint =.73 x 251,035 = 183,256
About 30 percent of all occupants involved in towaway rear impact crashes receive a whiplash injury. In towaway rear impact crashes (see Table V-3), the whiplash injury rates for integral and adjustable head restraints for LTVs and PCs did not show any predictable pattern as a function of occupant height. Part of the problem is the scarcity of data points. The actual number of cases are provided in the "whiplash raw" columns. Those cells with less than 50 data points have very wide confidence intervals around them compared to those cells with hundreds of cases. The results are counterintuitive compared to past agency evaluation findings, based on towaway and non-towaway crashes, that integral head restraints were more effective than adjustable head restraints due to a large portion of occupants not pulling up their adjustable head restraints. On average, for passenger cars the whiplash injury rate (31.75 per hundred occupants in towaway rear impacts) for integral head restraints was higher than the whiplash injury rate (27.99) for adjustable head restraints. For LTVs, the average whiplash rate (30.57) for adjustable head restraints was slightly higher than the whiplash injury rate (30.53) for integral head restraints.
For individuals 5 feet 9 inches and shorter in front outboard seats, the whiplash injury rates (37.94 and 31.0) were higher in passenger cars than the front outboard whiplash injury rates (17.14 and 20.65) in light trucks and vans with fewer data points.
For height 5 feet 10 inches and over LTVs had higher whiplash injury rates than passenger cars for both adjustable and integral head restraints. The LTVs whiplash injury rate for integral head restraints was 56.71 for front outboard seats, while for passenger cars the integral head restraint injury rate was 35.72. For adjustable head restraints, the whiplash injury rate for LTVs was 30.19, and the whiplash injury rate for cars was 28.04. These differences in rates are generally not statistically significant. There are two statistically significant comparison in the data set. 1) For integral head restraints in trucks, when comparing tall individuals with short individuals, the injury rates of 17.14 versus 56.71 are statistically significant. 2) For integral head restraints in the front outboard seating, the injury rates for short individuals in cars versus those in trucks (37.94 and 17.14 respectively) are statistically significant. The following is a breakout of the differences in selected whiplash rates for the period 1988 to 1996.
Front and Back Outboard Occupants
|Car||Integral vs Adjustable||31.75||27.99|
|Truck||Integral vs Adjustable||30.53||30.57|
|Integral||Car vs Truck||31.75||30.53|
|Adjustable||Car vs Truck||27.99||30.57|
Front Outboard only
|Car||Short||Integral vs Adjustable||37.94||31.00|
|Car||Tall||Integral vs Adjustable||35.72||28.04|
|Car||Integral||Short vs Tall||37.94||35.72|
|Car||Adjustable||Short vs Tall||31.00||28.04|
|Truck||Short||Integral vs Adjustable||17.14||20.65|
|Truck||Tall||Integral vs Adjustable||56.71||30.19|
|Truck||Integral||Short vs Tall||17.14||56.71*|
|Truck||Adjustable||Short vs Tall||20.65||30.19|
Front Outboard only
|Integral||Short||Car vs Truck||37.94||17.14*|
|Integral||Tall||Car vs Truck||35.72||56.71|
|Adjustable||Short||Car vs Truck||31.00||20.65|
|Adjustable||Tall||Car vs truck||28.04||30.19|
* difference is significant at 0.05
|Height ins.||Seat Position||Whiplash raw||Whiplash weighted||Whiplash rate*|
|5 ft 9 ins & under||Front outboard||152||8,937||37.94|
|5 ft 9 ins & under||Back outboard||10||407||11.59|
|5 ft 10 ins & over||Front outboard||49||3,172||35.72|
|5 ft 10 ins & over||Back outboard||2||86||44.85|
|Total||240||13,290||31.75||* Whiplash rate is the number of whiplash injuries per 100 occupants in rear impacts.|
Cars With Adjustable Head Restraints in Nonrollover Rear Impacts 1988 - 1996 NASS Annualized Data in Towaway Crashes
|Height ins.||Seat Position||Whiplash raw||Whiplash weighted||Whiplash rate|
|5 ft 9 ins & under||Front outboard||607||29,193||31.0|
|5 ft 9 ins & under||Back outboard||1||6||1.10|
|5 ft 10 ins & over||Front outboard||232||9,932||28.04|
LTVs With Integral Head Restraints in Nonrollover Rear Impacts 1988 - 1996 NASS Annualized Data in Towaway Crashes
|Height ins.||Seat Position||Whiplash raw||Whiplash weighted||Whiplash rate|
|5 ft 9 ins & under||Front outboard||46||926||17.14|
|5 ft 10 ins & over||Front outboard||23||2,058||56.71|
LTVs With Adjustable Head Restraints in Nonrollover Rear Impacts 1988 - 1996 NASS Annualized Data in Towaway Crashes
|Height ins.||Seat Position||Whiplash raw||Whiplash weighted||Whiplash rate|
|5 ft 9 ins & under||Front outboard||14||413||20.65|
|5 ft 10 ins & over||Front outboard||9||286||30.19|
IIHS has conducted surveys of head restraints in 1995, 1997 and 1998, Table V-4(a) and (b) show the 1998 data broken out by vehicle models and the IIHS ratings for the head restraints. The IIHS rating criteria depends upon the height and backset of the head restraint (see Figure 2).
|Type of vehicle||Number of Models by Ratings|
Head Restraint Evaluations as a Percent, 1998 Vehicles Model
|Type of vehicle||Ratings|
Because of variations in the shapes of head restraints, it is not possible to accurately correlate head restraint height as measured by IIHS and the height as measured by the method in FMVSS 202. The IIHS method measures the height as the distance down from the top of the head and the FMVSS 202 method measures up from the H-point along the torso line. Assuming an idealized head restraint shape, a simple relationship between the two measurement methods can be developed as shown in Figure 1. Figure 2 is a graphical depiction of how head restraints of 700mm (27.5 inch), 750 mm (29.5 inch) and 800 mm (31.5 inch) fare with respect to the IIHS dimensional rating technique. For any backset up to 70 mm (2.8 inch), the 800 mm (31.5 inch) high head restraint is always rated "good." A 700 mm (27.5 inch) high head restraint can never be rated better than poor for any backset. A 750 mm (29.5 inch) high head restraint is "good" for backsets up to 30 mm (1.2 inch) and "acceptable" for backsets up to 73 mm (2.9 inch).
The Insurance Institute for Highway Safety study on head restraints compared the neck injury rate of restraints rated as good to those rated as poor, acceptable to poor and marginal to poor using logistic regression based on damage severity and other factors. For both male and female drivers, head restraints rated as good were associated with a lesser likelihood of neck injuries than head restraints rated poor. The study found the following results:
Logistic Regression on the Odds of Neck Injury - Odds Ratios, Tort and Add-on States Only
|Effect||Male Driver||Female Driver||Total|
|Good vs. poor||0.90*||0.64**||0.76**|
|Acceptable vs. poor||1.53**||0.63||0.92|
|Marginal vs. poor||1.17||0.88||1.00|
|* A 0.90 measurement means that male drivers in models rated as good had a 10 percent
lower risk of neck injury than in vehicles rated poor.
** Statistically significant difference
Using the IIHS criteria, moving the height of the head restraint to 800 mm (31.5 inches) and a backset of less than 50 mm (two inches) would put the fleet of current restraints into the good category. According to IIHS, comparing a "Good" head restraint to a "Poor" head restraint would show a reduction of approximately 24 percent in whiplash injuries. Even though this result is shown to be statistically significant, the agency is not convinced of the magnitude of the result, because the "Good" category is made up of only three models that are all Volvos.
Similarly, there are 5 models in the acceptable category, and it is hard to believe that there is a 53 percent higher rate of injury for males in vehicles rated acceptable compared to those rated poor. However, the agency believes the results of this study are directionally correct. Based on this belief, the agency is proposing to require higher head restraints and a backset requirement. However, at this time the agency does not believe there are enough data, due to the lack of "Good" head restraints in the fleet, to present a convincing statistical argument as a basis for estimating the benefits of backset in its proposal.
Previous agency estimates of the effectiveness of head restraints (although these estimates were calculated in 1982, they are the only available estimates of effectiveness) indicated that for adult drivers in rear impact crashes, integral head restraints were 17 percent effective in preventing rear impact injuries and adjustable head restraints were 10 percent effective under the same conditions (see page II-1). As discussed earlier, these estimate have to be divided by 0.60 (see page II-2) to get the effectiveness for whiplash injuries alone (28.3 percent for integral restraints and 16.7 percent for adjustable restraints). Based on calculations shown later in the analysis, the average front outboard seat effectiveness for whiplash injuries over the 1988-96 time would be 20.2 percent (63,491/314,526). Kahane has postulated that an increase in restraint height from 27 to 31 inches would give an additional 9.5 percentage point reduction (based on a curvilinear relationship) in injuries (7)(see Table V-6 and Footnote7). Again, this estimate must be divided by 0.60 to get the effectiveness for whiplash injuries alone. This would result in a 15.8 percent(9.5/0.6) reduction in whiplash injuries. [Throughout the rest of the benefit section, there will be references to the Kahane report and these estimates will be divided by 0.60 to translate from effectiveness in any rear impact injury to effectiveness for whiplash injuries].
The agency also believes that there would be an increase in effectiveness for the backset requirement. NHTSA believes the proposal for backset will result in an increase in effectiveness based on several factors. First, studies have found that if the head is against the head restraint the occupant did not suffer any whiplash symptoms. Second, NHTSA computer generated models have shown that the reduction of the backset and an increase in the height of the head restraint reduces the level of neck loading and relative head to torso motion which may be related to the incidence of whiplash injuries. Third, the IIHS study comparing good, acceptable and poor head restraints and neck injuries gives an indication that backset is related to injury risk. The agency believes that reducing backset will reduce the injury rate. The agency does not have a reliable method of estimating the level of expected injury reduction from reducing backset at this time. Given that it is not possible to estimate the effectiveness of the backset at this time, the agency will calculate benefits based on the height requirements only.
INJURY REDUCTION - RELATIVE TO
CURRENT STANDARD 202 CARS - FOR INTEGRAL
RESTRAINTS BY SEATBACK HEIGHT
|Uniform Height of
|Improvement over current FMVSS 202 Cars (%)|
|Source: Kahane, C., "An Evaluation of Head Restraints, Federal Motor Vehicle Safety Standard 202" NHTSA, February 1982, DOT HS-806-108, Pg 46. *These were calculated after Kahane's analysis, to be used in this Head Restraint analysis.|
As shown in Table IV-2, the agency has estimated that the present fleet of vehicles has an average front seat outboard head restraint maximum height of 30.2 inches (1.3 inches less than the proposed 31.5 inches). Based on the 1982 evaluation by Kahane (see Table V-6), it is estimated that raising the height of the head restraint from 30.2 inches to 31.5 inches in the fleet will result in increased effectiveness against injury of 1.1 percentage points for rear impact injuries (derived by subtracting the effectiveness of the lower height from the effectiveness of the higher height in Table V-6) and a 1.83 (1.1/0.6) percentage point increase for whiplash injuries above the present fleet effectiveness. Note that these estimates were calculated for integral head restraints, but this proposal has a minimum height requirement for adjustable head restraints. Thus, for analysis purposes it is assumed that the adjustable head restraints perform as integral head restraints.
The agency also attempted to determine what percent of the population would benefit from a 31.5 inch height, in comparison to a 30.2 inch height. Data exist on sitting height for 5th females, 50th males and 95th males. The current standard of 700 mm (27.5 inches) will be above the C.G. of a 50th male up to a 8 mm backset. Similarly, 800 mm (31.5 inches) height will cover a 95th male up to a backset of 133 mm (5.2 inches) and 750 mm (29.5 inches) height will cover a 50th male up to a backset of 125 mm (4.9 inches). If we restrict backset to 50 mm (2 inches), a 767.1 mm (30.2 inches) high head restraint will cover a 95th male, i.e., it covers 95 percent of the male population.
Using the equation from Figure 1, a 767.1 mm (30.2 inches) high restraint and a 50 mm (2 inches) backset would be 50 mm below the top of a 50th percentile head and above the C.G. of a 95th percentile male head. Assuming 15 percent of males and no females (7.5 percent of the population) received an average benefit of a 20.2 percent reduction in neck injuries, the overall benefit would be 1.52 (.202 x .075) percentage points. The two different methods result in a range of estimates from 1.52 to 1.83 percentage points reduction, averaging 1.68 for the front seat.
The 1.68 percentage point increase applies to integral head restraints and the proportion of adjustable head restraint users that have the head restraint adjusted in the up position. Based on a survey of 282 occupants, the agency found that 47 percent of those with an adjustable head restraint, had the head restraint in the down position. Another 51 percent of drivers raised their head restraints from the lowest position, but not necessarily to the highest position, and 2 percent were unknown. We are assuming that if a person takes time to raise the head restraint, he or she raises it to a position that is comfortable. We are further assuming that new position is the C.G. of the head. Thus, it is estimated that 53 percent had the head restraint in the up position.
The average lowest driver height for adjustable head restraints in the present fleet was 28.0 inches (the lowest height comes into play when the adjustable head restraint is in the down position). The requirement would be 750 mm (29.5 inches) for the lowest height. Based on the Evaluation by Kahane, it is estimated that raising the lowest height from 28.0 to 29.5 inches will result in a 3.5 percentage point increase in effectiveness for all rear impact injuries and 5.83 (3.5/0.6) percentage point increase in effectiveness for whiplash injuries above the present fleet effectiveness for adjustable head restraints. Based on the survey, the 5.83 percentage point increase applies to 47 percent of the occupants in vehicles with adjustable head restraints.
Determining the effectiveness of raising average head restraint height in the rear seat is a more involved process, because the baseline height of the seats are different in the rear seat and with more children sitting in the rear seat, the average height of rear seat occupants is not the same as front seat occupants.
In the Kahane evaluation, the average front seat height of pre-standard seats was 22 inches. The average height of adjustable front seat head restraints in the down position was 25.5 inches and the average height of front seat integral head restraints was 28 inches. Head restraint heights have increased over time. The average height in the lowest position for the front outboard position adjustable head restraints for the 14 MY 1999 vehicles measured was 28.0 inches. This is 2.5 inches higher than the adjustable head restraints low point in the late 1970's and the same height as the average integral restraint at that time.
In the rear seat, two sets of benefit estimates are needed. The first set is between no head restraint and current head restraints. The second set of benefit estimates is between current head restraints and the proposed standard. For the first set it is assumed that the height of the rear bench seat is the same as pre-standard front seats (22 inches). Based on the sample of vehicles measured, the current head restraints measured at the lowest head restraint height in the rear seat are 25.7 inches tall. Thus, the effect of increasing height from 22 to 25.7 inches was determined from the Kahane evaluation as an 8.8 percentage point improvement in effectiveness for all rear impacts or 14.67 percent for whiplash injuries (8.8/0.6). This 14.67 percent effectiveness represents the benefit of current rear head restraints and will be used to determine the number of injuries that would occur if no one had head restraints currently (see page V-3).
The second set of benefits is an incremental benefit of going from today's head restraints to the proposal. The average lowest head restraint height is 25.7 inches, 3.8 inches lower than the proposed 29.5 inches. Incidentally, 25.8 inches is the average of those models with adjustable rear head restraints in lowest position, and 25.6 inches is the average for those models without rear head restraints. The average height for all rear seats, those with and those without head restraints, is 25.7 inches. Based on the Kahane evaluation, going from 25.7 inches to 29.5 inches in the front seat would increase effectiveness by 13.1 percentage points for rear impact injuries and 21.8 (13.1/.6) percentage points for whiplash injuries. However, the occupancy rate of the rear seat in terms of height is much different than the front seat (see the following table, 34 percent of front seat occupants are 5'10" or more, while only 17 percent of rear seat occupants are 5'10" or more). At this time, the agency does not have sufficient data on whiplash injuries by height to confidently adjust the rear seat data.
|5'9" and under||5'10" and over||Total|
The first steps needed in order to calculate the number of whiplash injuries that could have been prevented if the requirements were in place is to determine the number prevented by restraints currently.
Injuries prevented=Restrained injuries X [Restraint Effectiveness/(1-Restraint Effectiveness)]
For front seat Integral head restraints
67,779 x 0.283/0.717 = 26,752 whiplash injuries prevented
potential injuries = 67,779 + 26,752 = 94,531
For front seat Adjustable head restraints
183,256 x 0.167/0.833 = 36,739 injuries prevented
potential injuries = 183,256 + 36,739 = 219,995
Total injuries prevented = 26,752 +36,739 = 63,491
Total front seat potential injuries = 94,531 + 219,995 = 314,526
Average effectiveness in 1988-96 = 63,491/314,526 = 20.2 percent for the front seat head restraints.
Estimated front seat benefits are:
Total front seat benefits = 9,575 whiplash injuries reduced annually.
In the front seat, the effectiveness estimate is an increase above the current head restraint. For the rear seat, the 21.8 percentage point overall effectiveness is a combined increase of adding a head restraint in some models and increasing the height of the current head restraint in other models to move the current head restraints from an overall average height of 25.7 inches up to 29.5 inches.
For the rear seat there are an estimated 21,429 (see page V-3) potential whiplash injuries if there were no head restraints. Thus, the benefit for head restraints in the rear seat is 21,429 x 0.218 = 4,672 whiplash injuries reduced.
Total benefits are 9,575 benefits in the front seat plus 4,672 benefits in the rear seat = 14,247 whiplash injuries reduced annually.
The agency assumes the same safety benefits for the dynamic compliance option because it restricts head-to-torso motion to the same limit as the height and backset.
Whiplash Injury Costs
The average economic cost (excluding property damage) of a whiplash injury, in 1998 dollars, is estimated to be $6,485 (8), resulting in a total annual cost of approximately $1.77 billion for 272,088 whiplash injuries. The $6,485 estimate is based on the maximum injury per occupant being an AIS 1 injury. For this analysis, the agency examined all whiplash injuries, whether they were the highest AIS level or not. Although whiplash is usually an AIS 1 neck injury a small percentage of injuries in table V-6 were labeled as AIS greater than 1. Table V-7 shows the distribution of occupant injuries of those in rear impact towaway crashes.
|Whiplash Injury Only (AIS 1)||34.2%|
|AIS 1 Other than Whiplash||60.8|
|AIS Greater than 1||5.0|
The agency believes that the cost of $6,485 is a reasonable approximation for whiplash costs, even though it specifically represents MAIS 1 injuries for the following reasons: 1) very few of the occupants (about 5 percent in towaways and probably a much lower percentage in non-towaways) have injuries at a level higher than AIS 1; and 2) in rear impacts, a whiplash injury is likely to be the most costly AIS 1 injury and the longest lasting injury. Thus, using the MAIS 1 neck/head injuries as a proxy measure for rear impacts in which a whiplash occurs appears reasonable.
For the cost-effectiveness section, the agency uses comprehensive costs for an appropriate comparison between costs and benefits (see that section for further details).
In Table VI-1, costs estimates derived from tear down studies of a variety of motor vehicles are listed along with sales and total estimates. Although the cost estimates are from LTV's, they are the most recent estimates available and we do not believe there is much difference between the head restraint of a LTV and that of a passenger car. Therefore, we believe that the estimates for LTVs are a good proxy of the estimates for passenger cars.
Average unweighted consumer cost = $32.28 ($451.94/14)
Sales weighted average cost = $83,821,086/2,847,686=$29.44
Sales weighted average of Integral head restraints= $26,213,349/870,443=$30.12
Sales weighted average of adjustable head restraints=$57,607,737/1,977,243=$29.14
Data from Table VI-1 and additional data from the study are used to calculate the cost per inch of head restraint (see Table VI-2). Table VI-2 (9)gives the tear-down cost per inch of head restraint. Although in most cases the height increase necessary to pass the proposal is assumed to be attained by increasing the height of the head restraint, for some seat designs, the height increase can only be attained by increasing the seat back height. The agency has taken this into consideration, and believes that Table VI-2 is a representative sample of the vehicles in the fleet.
Cost Estimates of MY 1992 Head Restraints both Driver and Passenger
|Head Restraint System||Consumer Costs$
|1998 Model Sales|
|Chevy S10 PU /Integral||26.40||28.99||214,314|
|Ford Econoline /Integral||24.37||26.76||156,924|
|Ford Explorer /Integral||28.12||30.88||390,460|
|Toyota Previa/Sienna /Integral||58.04||63.73||14,723|
|Ford F150 PU /Adjustable||28.11||30.87||723,867|
|Dodge Caravan /Adjustable||35.51||38.99||268,238|
|Town and Country/ Adjustable||35.51||38.99||65,679|
|Jeep Cherokee/ Adjustable||31.98||35.11||134,031|
|Isuzu PU /Adjustable||19.81||21.75||13,419|
|Chevy Silverado /Adjustable||16.86||18.51||40,890|
Cost Per Inch of Head Restraint
|Head Restraint System||Total consumer cost both driver and front passenger||net cost per restraint less any adjustment hardware and assembly cost||height of restraint system studied||consumer cost per inch|
|Chevy S10/ Sonoma PU Integral||28.99||26.21/2=13.11||11 inches||$1.19/inch|
|Ford Econoline Integral||26.76||25.69/2=12.85||10-3/4 inches||$1.20/inch|
|Ford Explorer Mountineer/Integral||30.88||30.16/2=15.08||9-3/4 inches||$1.55/inch|
|Toyota Previa Integral||63.73||52.77/2=26.39||9 inches||$2.93/inch|
|Ford F150 PU Adjustable||30.87||20.18/2=10.09||9 inches||$1.12/inch|
|Dodge Caravan Voyager/Town Country Adjustable||38.99||28.37/2=14.19||4-3/4 inches||$2.99/inch|
|Jeep Cherokee Adjustable||35.11||29.51/2=14.76||7 inches||$2.11/inch|
|Isusu PU Adjustable||21.75||16.34/2=8.17||7-3/4 inches||$1.05/inch|
|Chevy CK/Sierra Silverado Adjustable||18.51||13.79/2=6.90||6-3/4 inches||$1.02/inch|
Data from Table VI-2 are used to calculate average cost per inch of head restraints.
Weighted average vehicle cost per inch of head restraint in 1998 dollars
Weighted average vehicle cost per inch of Integral head restraints in 1998 dollars =$1,219,254/870,443 =$1.40
Weighted average vehicle cost per inch of adjustable head restraints in 1998 dollars = $3,117,838/1,997,243 =$1.56
These data indicate that there is little difference in the cost of head restraints and that there is little difference in the cost per inch of head restraints between integral and adjustable head restraints. The average cost of $14.72 per head restraint and $1.54 per inch of head restraint is appropriate for this analysis.
Tables IV-1, 2, and 3 present data on the difference between the proposal and measurements taken on 14 MY 1999 models of head restraint height and backset. For example, the MY 1999 Toyota Camry was measured and the driver' seat highest head restraint position was 30.75 inches or 0.75 inches lower than the proposed height of 31.5 inches.
It is assumed that the cost increase of raising the height of head restraints is the cost of increasing the highest head restraint position up to the 800 mm (31.5 inches) in the front seat or to 750 mm (29.5 inches) in the rear seat. The agency has not added any cost to increase the front seat minimum height up to the 29.5 inch minimum. Since the cost of head restraints was very similar between adjustable and integral head restraints, the agency assumes that the true cost will be to raise the highest height of the head restraint and that changes in design, at no additional variable cost, can be accomplished to cover the minimum height requirements. Comments are requested on these assumptions.
Light vehicle sales in the U.S. totaled 15.55 million units in 1998. There were 8.14 million car sales and 7.40 million truck sales in the U.S. in 1998. All of these vehicles will have to have the height of the front seat head restraints increased. The cost of raising front seat head restraints an average of 1.3 inches (see Table IV-2) is $4.00 per vehicle (1.3 x 2 head restraints x $1.54) per inch. This results in a fleet cost of $62.2 million ($4.00 x 15.55 million).
Approximately 41 percent of the 1999 model year vehicles have head restraints in the rear seats and 20 percent have no rear seats (e.g., pickup trucks with no rear seats). Therefore, approximately 39 percent (1 - .41 - .20) of the vehicles which have no head restraint in the rear seat will need a new rear seat head restraint, while approximately 41 percent will need to have their current rear seat head restraint height increased.
The number of vehicles with no rear head restraint that need a head restraint equals approximately 6.065 (15.55 x 0.39) million units. The cost of making integral head restraints by raising the rear seat an average of 3.9 inches (see Table IV-2) equals $12.01 per vehicle (2 seats x 3.9 inches x $1.54 cost per inch per seat). This results in a fleet cost of $72.8 million ($12.01 x 6.065 million).
The number of vehicles that might need the rear head restraint raised equals 6.376 (15.55 x 0.41) million. The cost of raising these rear head restraints an average of 1 inches (see Table IV-2) equals $3.08 per vehicle (2 seats x 1 inches x $1.54 cost per inch per seat). This results in a fleet cost of $19.6 million ($3.08 x 6.376 million).
The agency also believes that there will be a small cost to add locking mechanisms to those head restraints that don't have locking mechanisms. These are simple devices for height adjustment locking that are estimated to cost about $0.15 per head restraint. Based on our survey of 14 vehicles, half of the adjustable head restraints had locking mechanisms (6 of 12 in the front seat and 3 of 6 in the rear seat). Assuming about 70 percent (see Table V-2) of the fleet will have adjustable head restraints in the front seat, and 70 percent of the vehicles with rear seats (80 percent) will have adjustable head restraints in the rear seat, the estimated cost for locking mechanisms is:
The combined total is $5.9 million for locking mechanisms for height. The agency believes that there are positive benefits to be gained from the locking mechanism, but at this time the agency is unable to calculate the benefits of adding a locking mechanism to the head restraint.
It is believed that the mechanism that allows an adjustable head restraint to tilt forward can easily be designed to lock the head restraint in that position at no additional cost. Comments are requested on this assumption.
The total estimated cost for head restraints to meet the proposal equals
Front Seat Head Restraints $62.2 million +
No Rear Head Restraint $72.8 million
Rear Seat Restraint Raised Average of 1 inch $19.6 million
Locking Mechanism for height $5.9 million
Total = $160.5 million.
The cost for the front seat is $65.5 million and the cost for the rear seat is $95.0 million. The
average costs per vehicle are estimated to be:
$4.21 ($65.5/15.55) in front seats
$3.61 ($20.15/6.376) in rear seats for vehicles with rear head restraints
$12.34 ($74.85/6.065) for vehicles with no rear head restraints
$10.32 (160.5/15.55) per average vehicle.
The agency believes that the backset requirements will not add cost to the vehicle. There will be some redesign costs to both increase the height and reduce the backset, but the agency believes that the backset requirement is a design change that can be implemented at the same time as height is increased, with no increase in head restraint cost.
The agency has concluded that adding the backset requirement would not add significant cost to the certification testing. There is a one time capital expenditure of $7,250 for the ICBC (Insurance Corporation of British Columbia) headform test device. It took one of the agency technicians approximately 45 minutes at a cost of 34 dollars per hour to do one seating position. Total agency cost of testing 14 vehicles is approximately $1,428. Assuming that the ECE 25 height requirement is implemented, the compliance cost should be inconsequential. The benefit of adding a backset comes in the form of reduced loading on the neck. ICBC developed a tool for measuring backset. This ICBC headform is simply attached to the SAE H-point machine. The point of contact of the rearward projection of the head profile on the head restraint is taken as the backset dimension. This same device could be used to measure restraint height relative to the top of the head form rather than referenced from the H-point, as is currently done.
VII. COST EFFECTIVENESS
This section combines costs and benefits to provide a comparison of the estimated injuries prevented per dollar spent. It should be noted that costs occur when the vehicle is purchased, but the benefits accrue over the lifetime of the vehicle. Benefits must therefore be discounted to express their present value and put them on a common basis with costs.
In some instances, costs may exceed economic benefits, and in these cases, it is necessary to derive a net cost per equivalent fatality prevented. An equivalent fatality is defined as the sum of fatalities and nonfatal injuries prevented converted into fatality equivalents. This conversion is accomplished using the relative values of fatalities and injuries measured using a "willingness-to-pay" approach. This approach measures individuals' willingness to pay to avoid the risk of death or injury based on societal behavioral measures, such as pay differentials for more risky jobs.
Table VII-1 presents the relative estimated rational investment level to prevent one injury, by maximum injury severity. The data represent average costs for crash victims of all ages. AIS is an anatomically based system that classifies individual injuries by body region on a six point ordinal scale of risk to life. Whiplash injuries are assumed to be valued based on the relative costs of MAIS 1 head/face/neck injuries (10).
Comprehensive Fatality and Injury Relative Values
|Injury Severity||1994 Relative Value* per injury|
|MAIS 1||.0033 (only valid for whiplash injury)|
|*includes the economic cost components and valuation for reduced quality of life|
Table VII-1 shows the estimated equivalent fatalities for the height and backset changes to the head restraint. About 303 whiplash injuries (1/.0033) are estimated to be equivalent to one fatality.
|Injury Benefits||Equivalent Fatalities|
The following is an example of the calculation of the cost per equivalent fatalities for head restraints before discounting. Cost/Equivalent Fatal Before Discounting
Front Seat Head Restraint $65.5 million /31.6 = $2.07 million
Rear Seat Head Restraint $95.0 million /15.4 = $6.16 million
Total $160.5 million /47.0 = $3.41 million
Appendix V of the "Regulatory Program of the United States Government," April 1, 1990 - March 31,1991, sets out guidance for regulatory impact analyses. One of the guidelines deals with discounting the monetary values of benefits and costs occurring in different years to their present value so that they are comparable. Historically, the agency has discounted future benefits and costs when they were monetary in nature. For example, the agency has discounted future increases in fuel consumption due to the increased weight caused by safety countermeasures, or decreases in property damage crash costs when a crash avoidance standard reduced the incidence of crashes, such as with center high-mounted stop lamps. The agency has not assigned dollar values to the reduction in fatalities and injuries, thus those benefits have not been discounted. The agency performs a cost-effectiveness analysis resulting in an estimate of the cost per equivalent life saved, as shown on the previous pages. The guidelines state, "An attempt should be made to quantify all potential real incremental benefits to society in monetary terms of the maximum extent possible." For the purposes of the cost-effectiveness analysis, the Office of Management and Budget (0MB) has requested that the agency compound costs or discount the benefits to account for the different points in time that they occur.
There is general agreement within the economic community that the appropriate basis for determining discount rates is the marginal opportunity costs of lost or displaced funds. When these funds involve capital investment, the marginal, real rate of return on capital must be considered. However, when these funds represent lost consumption, the appropriate measure is the rate at which society is willing to trade off future for current consumption. This is referred to as the "social rate of time preference," and it is generally assumed that the consumption rate of interest, i.e. the real, after- tax rate of return on widely available savings instruments or investment opportunities, is the appropriate measure of its value.
Estimates of the social rate of time preference have been made by a number of authors. Robert Lind (11) estimated that the social rate of time preference is between zero and 6 percent, reflecting the rates of return on Treasury bills and stock market portfolios. More recently, Kolb and Sheraga (12) put the rate at between one and five percent, based on returns to stocks and three month Treasury bills. Moore and Viscusi (13) calculated a two percent real time rate of time preference for health, which they characterize as being consistent with financial market rates for the period covered by their study. Moore and Viscusi's estimate was derived by estimating the implicit discount rate for deferred health benefits exhibited by workers in their choice of job risk.
Four different discount values are shown as a sensitivity analysis. The 2 and 4 percent rates represent different estimates of the social rate of time preference for health and consumption. The 10 percent figure was required by 0MB Circular A-94, until October 29,1992. The 7 percent figure is the current OMB requirement, which represents the marginal pretax rate of return on an average investment in the private sector in recent years.
Safety benefits occur when there is a crash severe enough to potentially result in occupant death and injury, which could be at any time during the vehicle's lifetime. For this analysis, the agency assumes that the distribution of weighted yearly vehicle miles traveled are appropriate proxy measures for the distribution of such crashes over the vehicle's lifetime(see Tables VII-3(a and b)).
|Vehicle Age (years)||Vehicle Miles Traveled||Survival Probability||Weighted Vehicle
|7 Percent '
|Vehicle Age||Survival||Weighted||Fraction of||Discount||Discount|
Multiplying the percent of a vehicle's total lifetime mileage that occurs in each year by the discount factor and summing these percentages over the 20 (passenger cars) or 25 (LTV's) years of the vehicle's operating life, results in the following multipliers for the average of passenger cars and light trucks: 0.8871 at a 2 percent discount rate, 0.7946 at a 4 percent discount rate, 0.6844 at a 7 percent discount rate, and 0.5993 at a 10 percent discount rate. These values are multiplied by the equivalent lives saved to determine their present value (e.g., Table VII-4(a) 31.6 x 0.8871 = 28.0). The costs per equivalent life saved for passenger cars and light trucks are then recomputed and shown in Table VII-4(b) e.g., ($65.5 million/28.0=$2.3 million, $95.0 million/13.7=$6.9 million and 160.5/41.7=$3.8 million).
Equivalent Lives Saved
|Base Equivalent||2 percent||4 Percent||7 percent||10 percent|
|2 percent||4 percent||7 percent||10 percent|
|Front seat||$2.3 million||$2.6 million||$3.0 million||$3.5 million|
|Rear seat||$6.9 million||$7.8 million||$9.0 million||$10.4 million|
|Total||$3.8 million||$4.3 million||$5.0 million||$5.9 million|
Sensitivity analysis of benefits of reducing backset
The above estimates include no benefit for reducing backset, a very important part of the agency's proposal. However, the agency does not know how best to estimate the potential benefits of reducing backset. This section includes a sensitivity analysis to determine how beneficial reducing backset must be to make this proposal as cost-effective as others the agency has implemented. Essentially, the agency looks for rules to cost less than $2.7 million per equivalent life saved at the 7 percent discount rate. This is not an absolute measure of cost-effectiveness. The agency has approved many safety standards that have exceeded this level. However, it represents a rough guideline, based on the comprehensive value of preventing a fatality.
For front seat head restraints, the cost per equivalent life saved is $3.0 million at a 7 percent discount rate based on the effectiveness estimated for increasing the height of head restraints and assuming no benefit for backset. In order to have a cost per equivalent life saved of $2.7 million, there has to be 24.3 equivalent lives saved ($65.5/$2.7 million)(an increase in backset of 1.6 equivalent lives saved for backset i.e., 24.3-22.7, since further increases will have to come from the backset) at a 7 percent discount rate or 2.3 equivalent lives undiscounted (1.6/.6844). At 303 injuries per equivalent life saved, you need 697 (2.3x303) whiplash injuries reduced by backset. With a target population of 314,526 (see page V19) in the front seat, backset would have to be 0.2 percent effective to make the front seat head restraints cost-effective (697/314,526).
For rear seat head restraints, the cost is $94.9 million, the equivalent lives saved are 15.4 x .6844 at a 7 percent discount rate or 10.5 and the cost per equivalent life saved is $9.0 million. In order to have a cost per equivalent life saved of $2.7 million, you need 35.2 equivalent lives saved ($94.3 million/$2.7 million) (an increase of 24.7 equivalent lives saved for backset i.e., 35.2-10.5, since any further increases will have to come from the backset) at a 7 percent discount rate or 36.1 equivalent lives undiscounted.(24.7/.6844). At 303 injuries per equivalent life saved, you need 10,938 (36.1x303) whiplash injuries reduced by backset. With a target population of 21,294 in the rear seat, backset would have to be 51.4 percent effective to make rear seat head restraints cost-effective (10,938/21,294).
For both front and rear seats combined to be cost-effective, total savings for backset would have to be 11,635 whiplash injuries reduced out of a total target population of 335,820, or an effectiveness rate of 3.5(11,635/335,820) percent.
VIII. REGULATORY FLEXIBILITY ACT
The Regulatory Flexibility Act of 1980 (Public Law 96-354) requires agencies to evaluate the potential effects of their proposed and final rules on small businesses, small organizations and small government jurisdictions.
Section 603 of the Act requires agencies to prepare and make available for public comment a preliminary regulatory flexibility analysis (PRFA) describing the impact of proposed rules on small entities. Section 603(b)of the Act specifies the content of a PRFA. Each PRFA must contain:
NHTSA has considered the effects of this rulemaking action under the Regulatory Flexibility Act and hereby certify that the proposed amendment would not have a significant economic impact on a substantial number of small entities.
The proposed rule would directly affect motor vehicle manufacturers, alterers and seating manufacturers.
For passenger car and light truck manufacturers, NHTSA estimates that there are only about four small manufacturers in the United States. These manufacturers serve a niche market, and the agency believes that small manufacturers do not manufacture even 0.1 percent of total U.S. passenger car and light truck production per year.
The agency believes that there are any very few small seating manufacturers. While the proposed rule would not impose any requirements on these manufacturers, it would be expected to have an impact on these types of small businesses by changing the requirements for head restraints.
NHTSA notes that final stage vehicle manufacturers and alterers could also be affected by this proposal. Many final stage manufacturers and alterers install their own seats and seating systems in vehicles they produce. The proposal would not have any significant effect on final stage manufacturers or alterers.
Small organizations and small governmental units would not be significantly affected since the potential cost impacts associated with this proposed action should only slightly affect the price of new motor vehicles.
For the reasons discussed above, the small entities which would most likely be affected by this proposal are small vehicle manufacturers, seating manufacturers, final stage manufacturers and alterers.
The agency believes, further, that the economic impact on these manufacturers would be small. While the small vehicle manufacturers would face additional compliance costs, the agency believes that seating manufacturers would likely provide much of the engineering expertise necessary to meet the new requirements, thereby helping to keep the overall impacts small. The agency also notes that in the unlikely event that a small vehicle manufacturer or alterer did face substantial economic hardship, it could apply for a temporary exemption for up to three years. See 49 CFR Part 555. It could subsequently apply for a renewal of such an exemption.
UNFUNDED MANDATES REFORM ACT ANALYSIS
The Unfunded Mandates Reform Act of 1995 (Public Law 104-4) requires agencies to prepare a written assessment of the costs, benefits and other effects of proposed or final rules that include a Federal mandate likely to result in the expenditure by State, local or tribal governments, in the aggregate, or by the private sector, of more than $100 million annually.
These effects have been discussed in detail in previous sections of this Preliminary Economic Assessment, see e.g., sections on "Cost," "Benefits," and "Preliminary Regulatory Flexibility Analysis." To summarize, NHTSA is issuing this proposed rule to require head restraints be raised to an average of 800 mm (31.5 inches) in the front outboard positions and 750 mm (29.5 inches) in the rear outboard positions, also to have a back set of no less than 50 mm at any adjustment position under the authority of 49 U.S.C. 322, 30111, 30115, 30117 and 30166; delegation of authority at 49 CFR 1.50.
The proposed rule will would improve the safety of individuals traveling in passenger vehicles.
The cost of the proposed rule is estimated to be $147.7 million.
IX. Costs and Benefits of Head Restraints in Center Seating Positions
The agency has examined the implications of requiring a head restraint in both the front and rear center seating positions. The following is an analysis of head restraints in the center seating positions of passenger vehicles.
The data (see page VI-5) indicate that there is little difference in the cost per inch of head restraints between integral and adjustable head restraints. The average cost of $14.72 per head restraint and $1.54 per inch of head restraint estimated previously are used in this analysis.
Approximately 20 percent of the light vehicle fleet would be required to have a head restraint in the front center seating position. The number of vehicles that need a front center head restraint is 3.11 million (.2 x 15.55m). The average cost of current head restraints is $14.72. If the agency were to propose the same height for the center front seat head restraints as for front outboard head restraints, the average head restraint would have to be raised 1.3 inches to meet the 31.5 inch proposal. The cost of raising the average head restraint 1.3 inches is $2.00 (1.3 x $1.54). Average total cost of the front center head restraint is $16.72 ($14.72 + $2.00). Total cost of installing a front center head restraint and raising the height to meet the proposed rule is $52.00 million (3.11 million vehicles x $16.72).
The average height needed to be added to a center backseat head restraint was determined by examining the vehicles without adjustable head restraints in the rear seat from Table IV-1.
Table IX - 1
Vehicles Without Adjustable Head Restraints -- Rear Center seat
|Vehicles||Inches to be Raised||1998 Sales||Sales Weighted Inches|
|* The weighted average number of inches the head restraint needed to be raised was 4.976 (6,564,734/1,319,188) inches.|
Light vehicle sales in the U.S. totaled 15.55 million units in 1998. There were 8.14 million car sales and 7.40 truck sales in the U.S. in 1998. Approximately 79 percent of these vehicles will have to have the rear center position installed with a head restraint (some vehicles do not have rear seat or center seating position). The number of vehicles that would need to have the rear center seat raised is approximately 12.29 (.79 x 15.55) million. The cost of raising the rear center seat an average of 4.976 inches is approximately $7.66 ($1.54 x 4.976) per vehicle. The total cost of raising the rear center seat to meet the height of the proposed regulation is $94.14 million ($7.66 x 12.29 million vehicles).
Total cost of front and rear center seats head restraints is $146.14million ($52.00 + $94.14).
Table IX - 2
Whiplash Injuries in Center Seating Positions
(Based on Tow-away Crashes in NASS-CDS 1988 to 1996)
|Body-type||Seat Position||Whiplash Raw||Annual Average Whiplash Weighted|
|Light Truck||Front Center||2||316|
|Light Truck||Back Center||2||149|
There were an annual average of 449 whiplash injuries in the front center seating position and 1,512 whiplash injuries in the rear center seating position in tow-away crashes. On average, the multiplier for tow-away crash injuries to total injuries in police reported crashes is 3.0 (see V-2). Thus, we estimate the annual estimated number of police-reported whiplash injuries in the front center seat in rear crashes to be 1,347 (449 x 3.0). The multiplier from police-reported crashes to all crashes, including unreported crashes, for AIS 1 injuries is 1.29 (see V-2). Thus, the annual estimated number of total whiplash injuries in the front center seat, in rear crashes, police-reported and unreported is 1,738 (1,347 x 1.29).
Similarly, for the rear center seating position, the estimated total number of whiplash injuries is 5,851 (1,512 x 3 x 1.29).
The effectiveness for head restraints is dependent upon the height of the head restraint. For the front center seat, the result of adding a head restraint and then raising the head restraint to the height 31.5 inches, the effectiveness would be an estimated 25.3 (15.2/0.6) percent (the effectiveness number is calculated from Kahane, C., "An Evaluation of Head Restraints, Federal Motor Vehicle Safety Standard 202" NHTSA, February 1982, DOT HS-806-108, Page 280 and Table V-6 of this document, which is an expanded version of kahane's Table B-6) . Thus, the benefits of head restraints in the front center seat is 1,738 x 0.253 = 440 whiplash injuries reduced
For the rear seat, the effectiveness of a 29.5 inch head restraint is estimated to be 21.8 percent (13.1/.6)(see Table V-6). Thus, the benefits of head restraints for the rear center seating position is estimated to be 5,851 x 0.218 = 1,276 whiplash injuries reduced.
Total benefits are: 440 whiplash injuries reduced in the front center seat plus 1,276 whiplash injuries reduced in the rear center seat = 1,716 whiplash injuries reduced annually.
Cost Per Equivalent Fatality
From Table VII-1, approximately 303 whiplash injuries are estimated to be equivalent to one fatality. Therefore, in the front center seat there are approximately 1.45 (440/303) equivalent fatalities. In the rear center seat there are approximately 4.21 (1,276/303) equivalent fatalities.
Cost /Equivalent Fatality Before Discounting
Front Center Seat Head Restraint $52.00 million /1.45 = $35.86 million
Rear Center Seat Head Restraint $94.14 million /4.21 = $22.36 million
Both Positions $146.14 million/5.66 = $25.82 million
As discussed in Chapter VII, benefits accrue over the twenty to twenty five years life time of the passenger vehicle while costs occur when the vehicle is purchased. Benefits are discounted to present value so that costs and benefits are compared on an equal basis.
Discounted Cost/Equivalent Fatality
Equivalent Lives Saved
|Base Equivalent||2 percent||4 Percent||7 percent||10 percent|
|Front Center 1.45||1.286||1.152||0.992||0.869|
|Rear Center 4.21||3.735||3.345||2.881||2.523|
|2 percent||4 percent||7 percent||10 percent|
|Front seat||$40.43 million||$45.13 million||$52.40 million||$59.84 million|
|Rear seat||$25.21 million||$28.14 million||$32.67 million||$37.32 million|
|Total||$29.11 million||$32.49 million||$37.73 million||$43.08 million|
For front center seat head restraints, the cost per equivalent life saved is $52.40 million at a 7 percent discount rate based on the effectiveness for increasing the height of head restraints and assuming no benefit for backset. For rear center seat head restraints, the cost is $32.67 million at a 7 percent discount rate. For both front and rear center seat combined, the cost per equivalent life saved is $37.73 million at a 7 percent discount rate.
Having center seat head restraints limits to some extent the driver's ability to observe traffic behind the vehicle using the rearview mirror. When a vehicle is in reverse, center head restraints limit visibility when the driver turns his/her head to back up. In addition a front center seat head restraint can limit vision through the right side second seat window when the driver is considering a lane change maneuver to the right. The agency can not quantify these potential losses in visibility, nor the potential impact this loss in visibility could have on safety.
The agency is not proposing to require center seat head restraints because of the significant costs, much higher cost per equivalent fatality than outboard positions, and because there are visibility concerns.
1. Kahane, C., "An Evaluation of Head Restraints, Federal Motor Vehicle Safety Standard 202" NHTSA, February 1982, DOT HS- 806-108, pg 46
2. Mats Y. Svensson, Per Lovsund, Yngve Haland and Stefan Larson, The Influence of Seat-Back and Head-Neck Motion During Rear-Impact presented at the 1993 International IRCOBI Conference on the Biomechanics of Impact, 8-10 September, Eindhoven, The Netherlands,
3. Olsson I, Bunketorp O, Gustafsson C, Planath I, Norin H, Ysander L, An In-Depth Study of Neck Injuries in Rear End Collisions 1990 International Conference on The Biomechanics of Impact.
4. Wheeler JB, Smith TA, Siegmund GP, Brault JR, King DJ. Validation of The Neck Injury Criterion (NIC) Using Kinematic and Clinical Results From Human Subjects in Rear-End Collision. IRCOBI Conference 1998.
5. Passenger vehicles include: passenger cars (PC), light trucks and vans (LTVs), which include pickups, vans and sport utility vehicles under 10,000 pounds GVWR.
6. "The Economic Cost of Motor Vehicle Crashes, 1994" NHTSA, DOT HS 808 425, July 1996, Pg. 9.
7. Kahane, C., "An Evaluation of Head Restraints, Federal Motor Vehicle Safety Standard 202" NHTSA, February 1982, DOT HS-806-108, Pg 46.
8. Blincoe, LJ The Economic Cost of Vehicle Crashes 1994, Washington, DC: U.S.Department of Transportation, NHTSA, DOT HS 808 425; 1996. Page 66, Appendix D, Section on Face, Other Head/Neck; Total Cost is $9,359 less property damage and travel delay($3,263+$203) is $5,893 in $1994. Using CPI all items multiplier the cost in $1998 is $6,485.
9. Fladmark, G. and Khadilkar, A., "Cost estimates of Head restraints in Light trucks/Vans and Cost Estimates of Lower Cost Antilock Brake Systems. Final Report, U.S. Department of Transportation, 22 July 1994, page 21.
10. The relative value of an MAIS 1 whiplash injury was estimated as follows: The "quality of life" portion of an MAIS 1 injury was computed by subtracting MAIS 1 economic costs from MAIS 1 comprehensive costs ($10,840-$7,243=$3,597). This was then added to the injury related portion of head/face/neck economic costs (see footnote 5). This calculation is:($9,359-$3,263-$203=$5,893), where $3,263 is property damage and $203 is travel delay. The result was an estimate of $9,490 ($3,597+$5,893) in comprehensive costs for an MAIS 1 whiplash injury. Dividing this by the total comprehensive costs for a fatality gives .0033 to four decimal places. The MAIS figures are taken from "The Economic Cost of Motor Vehicle Crashes 1994", pages 8, 59, and 66.
11. Lind, RC, "A primer on the Major Issues Relating to the Discount Rate for Evaluating National Energy Options," in Discounting for Time and Risks in Energy Policy, 1982, (Washington, D.C.,Resources for the Future, Inc.).
12. J. Kolb and J.D. Sheraga, "A Suggested Approach for Discounting the Benefits and Costs of Environmental Regulations," unpublished working papers.
13. Moore, M.J., and Viscusi, W.K.,"Discounting Environmental Health Risks: New Evidence and Policy Implications," Journal of Environmental Economics and Management, V.18, No. 2, March 1990, part 2 of 2.