Table II.1—Passenger Cars and Light Trucks Involved in Crashes, by Initial Point of Impact, Crash Severity, and Crash Type for Year 2020
Crash type by initial point of impact Crash severity Fatal Injury Property damage only Total Number Percent Number Percent Number Percent Number Percent Single-Vehicle Crashes: Front 10,883 67.9 358,800 77.1 791,913 73.1 1,161,597 74.2 Left Side 890 5.6 21,960 4.7 54,317 5.0 77,167 4.9 Right Side 886 5.5 33,795 7.3 85,283 7.9 119,965 7.7 Rear 222 1.4 16,334 3.5 84,915 7.8 101,473 6.5 Noncollision 1,714 10.7 27,237 5.9 40,898 3.8 69,849 4.5 Other/Unknown 1,430 8.9 7,157 1.5 25,991 2.4 34,580 2.2 Total 16,025 100.0 465,285 100.0 1,083,319 100.0 1,564,629 100.0 Multiple-Vehicle Crashes: Front 15,987 62.9 1,183,348 54.3 2,354,919 49.3 3,554,254 50.9 Left Side 3,221 12.7 224,185 10.3 522,635 10.9 750,041 10.7 Right Side 2,649 10.4 206,256 9.5 486,970 10.2 695,875 10.0 Rear 2,772 10.9 561,310 25.8 1,395,634 29.2 1,959,717 28.1 Noncollision 76 0.3 702 0.0 2,474 0.1 3,253 0.0 Other/Unknown 704 2.8 2,787 0.1 17,515 0.4 21,007 0.3 Total 25,409 100.0 2,178,589 100.0 4,780,149 100.0 6,984,146 100.0 All Crashes: Front 26,870 64.9 1,542,149 58.3 3,146,832 53.7 4,715,850 55.2 Left Side 4,111 9.9 246,145 9.3 576,953 9.8 827,209 9.7 Right Side 3,535 8.5 240,051 9.1 572,254 9.8 815,839 9.5 Rear 2,994 7.2 577,646 21.8 1,480,551 25.3 2,061,189 24.1 Noncollision 1,790 4.3 27,939 1.1 43,372 0.7 73,101 0.9 Other/Unknown 2,134 5.2 9,945 0.4 43,507 0.7 55,586 0.7 Total 41,434 100.0 2,643,874 100.0 5,863,467 100.0 8,548,775 100.0 Of the over 2 million rear impacted light vehicles in 2020, only 0.15% (2994/2,061,189) involved fatalities, as compared with 0.57% (26,870/4,715,850) of the 4.7 million front impacted light vehicles and 0.47% (7646/1,643,048) of the 1.6 million side impacted light vehicles involved fatalities; a fatal rear collision is typically associated with a high ΔV [21] collision.[22] However, the injury rate in light vehicles that underwent a rear collision in 2020 is comparable to other crash directions, as 30% of rear impacted light vehicles involved injury, while 33% of frontal and 30% of side impacted light vehicles involved injury.
The count of occupant injury and fatality for different collision directions is classified by vehicle type for year 2020 in table II.2 Traffic Safety Facts from FARS and CRSS. Restricting the discussion to light vehicles (passenger cars and light trucks), 6.1% of passenger car occupants and 4.6% of light truck occupants killed were due to rear impacts. The combined light vehicle total was 5.4%. In contrast to the light vehicle fatality rate, the percentage of fatalities in rear impacted large trucks was only 2.9%. This would be consistent with the expectation that rear impact ΔV for large trucks would be on average smaller than for light vehicles.[23]
Table II.2—Vehicle Occupants Killed and Injured, by Initial Point of Impact and Vehicle Type for Year 2020
Injury severity/initial point of impact Vehicle type Passenger cars Light trucks Large trucks Buses Other/ unknown Subtotal Motorcycles Total Occupants Killed: Front 7,724 5,997 523 6 273 14,523 3,444 17,967 Left Side 1,849 1,129 35 1 53 3,067 300 3,367 Right Side 1,633 840 50 0 52 2,575 259 2,834 Rear 822 474 24 1 70 1,391 242 1,633 Other 160 106 16 2 12 296 32 328 Noncollision 581 1,309 146 2 280 2,318 858 3,176 Unknown 703 497 37 4 125 1,366 444 1,810 Total 13,472 10,352 831 16 865 25,536 5,579 31,115 Occupants Injured: Front 696,221 440,711 21,175 1,958 3,023 1,163,087 41,952 1,205,039 Left Side 121,449 74,875 4,058 2,623 596 203,600 6,623 210,222 Right Side 109,313 77,510 4,429 920 447 192,620 5,863 198,483 Rear 273,123 194,857 9,136 1,096 698 478,909 4,765 483,675 Other 5,600 3,584 1,228 0 38 10,451 289 10,740 Noncollision 15,248 21,698 4,895 1 2,012 43,854 23,010 66,864 Unknown 381 274 13 23 34 725 26 751 Total 1,221,335 813,509 44,934 6,620 6,849 2,093,246 82,528 2,175,774 Further, according to the 2020 Traffic Safety Facts, 22.3% of passenger vehicle injuries occurred in rear impacts (light trucks = 24.0%, heavy trucks = 20.3%). For each vehicle type, the proportion of fatalities for rear impacts is significantly lower than the corresponding proportion of injuries for rear impacts, compared to other initial impact directions. The rear impact proportion of fatalities in light trucks and heavy trucks is lower than in passenger cars, but the rear impact proportion of injuries in light trucks is slightly greater than in passenger cars and heavy trucks. The disparity in rear collision proportion of injuries for different vehicle types is discussed in the literature review below.
B. CISS Data Analysis
NHTSA also examined the Crash Investigation Sampling System (CISS) data files for the years 2017-2020 to determine the number of rear impacts compared to other crash modes and determine the injury risk (number of injured occupants divided by the number of exposed occupants) of vehicle occupants in rear impacts. These data are limited because CISS currently reports only police reported, tow-away crashes, and, as will be explained later, most rear impacts are not tow-aways. The data were divided into different crash types: rollover, frontal, side, rear, other, and unknown. In addition, for rear impacts, the data were segmented by the change in velocity of the impacted vehicle (ΔV). All data presented here are weighted to represent national estimates. The maximum abbreviated injury scale [24] (MAIS) for each injured occupant is presented so that an occupant with multiple injuries is counted only once in the analysis. An occupant was counted as having a whiplash injury (MAIS 1 neck injury) even if they had other AIS 1 injuries. Crashes with fire have been excluded from the sample. If an occupant had a whiplash injury but also had a MAIS 2+ injury, they were not added to the whiplash injury count. As was the case for the FARS and CRSS data above, we have not restricted the data by seating row.
The total annualized number of involved individuals was estimated to be 4.5 million, including crash types categorized as “unknown” and “other.” Rear impact crashes accounted for only 373,237 or 8.3% of all tow-away crash involving individuals in the CISS database (Figure II.1). Only rollover crashes yield fewer occupants involved in tow-away crashes. Looking at the proportion of occupants with serious and higher severity injuries (MAIS 3-6) by crash type, we see that MAIS 3-6 are underrepresented in rear impacts (4.3% = 3,814/88,437) and overrepresented in rollover (19.7% = 17,415/88,437). By contrast whiplash injury is overrepresented in rear impacts (15.8% = 31,206/197,060) as compared to the number of towed rear impacts.
Figure II.2 and Figure II.3 show the risk of MAIS 3-6 and whiplash injury [25] for each towed crash mode. The risk of MAIS 3-6 injury in rear impacts is 1.0% (= 3,814/373,237), which is about 60% of the next highest risk (1.7% for side). The whiplash injury risk in rear impacts is approximately 8.4% (= 31,206/373,237), which is about 1.5 times the next highest risk (5.7% for rollover). These whiplash injury rates do not consider non-towed crashes, where the majority of whiplash injuries are known to occur.[26]
Figure II.4 shows the distribution of towed rear impacts by the change in velocity of the rear impacted vehicle. Most of the crashes are in the 11-20 kilometers per hour (km/h) (6.8-12.4 miles per hour (mph)) ΔV range. Table II.3 provides tabulated annual occupant injuries in rear collisions according to injury severity and ΔV. For occupants in a known ΔV rear impact crash, the majority of injuries are estimated to be no injury (MAIS 0) in all ΔV ranges. The most probable known ΔV range for injury of any type is the 11-20 km/h (6.8-12.4 mph) category, which is consistent with this being the most common impact speed range. More than three-quarters of MAIS 3+ rear impact injuries occur above 31 km/h (19.3 mph). Figure II.5 gives the risk of MAIS 2 and MAIS 3+ injuries as a function of impact ΔV in towed rear crashes. The highest risk for MAIS 2 injuries is 8.4% (= 891/10,630) for 51+ km/h (31.7+ mph) ΔV crashes. The highest risk for MAIS 3+ is 7.0% (= 1,572/22,425) for the 31-40 km/h (19.3-24.9 mph) ΔV range. Figure II.6 shows that for whiplash, the highest risk is 11.7% (= 2,624/22,425) for injury in towed crashes occurring in the 26-35 km/h (16.2-21.8 mph) range. The risk at 51+ km/h is similar at 11.1% (= 1,183/10,630) and at other speeds is between 2.8% and 9.7%.
Table II.4—Annual Rear Impact Injury by ΔV
[2017-2020 CISS]
ΔV (km/h) MAIS 0 Whiplash MAIS 1 no whiplash MAIS 2 MAIS 3-6 Total Unknown 101,022 12,637 13,950 4,495 789 132,893 0-10 22,057 675 913 59 0 23,704 11-20 88,352 7,680 15,469 2,793 474 114,769 21-30 46,618 6,302 10,429 1,455 249 65,052 31-40 13,085 2,624 4,157 988 1,572 22,425 41-50 1,811 107 1,661 94 92 3,764 51+ 5,173 1,183 2,746 891 638 10,630 Total Known ΔV 177,095 18,569 35,375 6,279 3,025 240,345 Total 278,117 31,206 49,325 10,775 3,813 373,237 
Figure II.6 provides the whiplash injury rates for towed crashes. CISS does not collect injury data for non-towed crashes. In 2004, using State data, the Final Regulatory Impact Analysis for the upgrade of FMVSS No. 202 found four times as many whiplash injuries in all crashes compared to those in tow-away crashes. NHTSA plans to update this analysis to accurately represent the current whiplash injury risk. Older field data, however, are still useful to provide a sense of the very large proportion of whiplash injuries that occur at low speed.
With historical data, we can attempt to generate estimates that include non-towed whiplash. Between 1982 and 1986, non-towed crash data were collected. Table II.5 shows the distribution of an approximation of whiplash injuries occurring in towed and non-towed impacts for the 1982-86 National Automotive Sampling System (NASS) data. The greatest ratio of non-towed to towed whiplashes was 20 times for the 0-10 km/h (0-6.2 mph) ΔV range. The next highest ratio was for the 11-20 km/h (6.8-12.4 mph) range at 8 times.[27] As expected, this ratio drops significantly at higher speeds because there are fewer non-towed crashes at these speeds. If we use the ratio of NASS data for non-towed to towed crashes as a multiplier for the CISS towed whiplash injury estimates in each speed range to attempt to account for the non-towed whiplash injuries in the newer data set, the result is column four in table II.5. If we distribute proportionally the cases of whiplash injuries where the impact speed was unknown to the known cases, the result is given in the fifth column. In this column we see that more than three-quarters (125,221/161,623) of all whiplash injuries occur at impact ΔV less than 20 km/h (12.4 mph). For only towaway rear impacts (not shown graphically) this ΔV limit captures 45% (8,355/18,570) of whiplash injuries. The whiplash injury distribution is shown graphically in Figure II.7. This estimate is provided to give a general sense of how considering whiplash injury only in tow-away crashes significantly underestimates overall whiplash injury distribution, particularly for lower speed crashes. This estimate comes with a large degree of uncertainty because it is based on historical NASS data.
Table II.5—Adjustments to Whiplash Injuries To Account for Non-Towed Crashes
ΔV (km/h) Ratio total to towed (82-86 NASS) Towed whiplash injury (2017-2020 CISS) Compensated whiplash injury Unknown ΔV distributed Unknown 5.1 12,637 64,553 0-10 19.8 675 13,339 22,210 11-20 8.1 7,680 61,868 103,011 21-30 2.8 6,302 17,550 29,220 31-40 1.1 2,624 2,768 4,609 41-50 1.0 107 110 184 51+ 1.0 1,183 1,183 1,972 Total Known ΔV 18,570 96,819 Total 31,207 161,372 161,372 
C. Field Data Analyses From Relevant Literature
In an earlier 1997 study of the National Automotive Sampling System-Crashworthiness Data System (NASS-CDS) across years 1980-1994, Prasad [28] found that rear impact collisions accounted for 11% of all possible struck vehicle scenarios. The distribution of crashes indicated that 50% of all rear impacts occur at ΔVs of 21 km/h (13 mph) or less, 86% occur at ΔVs less than 32 km/h (20 mph) and 94% occur at ΔVs of 40 km/h (25 mph) or less. Furthermore, when examining the distribution of injuries, it was found that less than 1% of rear end collisions resulted in severe injury of AIS 3 or more.
In another study, Parenteau [29] examined 1999 to 2015 NASS-CDS crash data to investigate the risk for MAIS 3+ outcomes including fatalities in crashes involving vehicles from model year (MY) 2000 and later. The risk for severe injury was lowest in rear crashes. The authors found head trauma to be the most likely severe injury for frontal passengers in rear collisions, followed by thorax and spinal injuries. The severe injuries were mostly the result of contact with the windshield, head restraint, and B-pillar. Many of these severe injuries develop from a seat retention issue (such as not wearing a seat belt) in which the occupant decouples from the seating system. It is unclear to what extent seat strength and retention issues overlap. The most severe injuries were attributed to forward intrusion of rear components.
Most rear collisions lead to a relatively low ΔV of the struck vehicle and this contributes to moderating injury of the vehicle occupants. The characteristics of the struck vehicle affect the injury severity and fatality risk of the occupants. As discussed in the next section, the majority of reported rear collision injuries are cervical injuries with or without clear pathology, while a small percentage of rear collisions are associated with high ΔV and severe injuries.
III. Statutory and Regulatory Background
A. The Safety Act and the Infrastructure, Investment and Jobs Act
Congress enacted the Safety Act for the purpose of “reduc[ing] traffic accidents and deaths and injuries resulting from traffic accidents.” [30] To accomplish this, the Safety Act authorizes the Secretary of Transportation to promulgate FMVSSs as well as to engage in other activities such as research and development. The Secretary has delegated the authority for implementing the Safety Act to NHTSA.[31] The Safety Act requires that FMVSSs “be practicable, meet the need for motor vehicle safety, and be stated in objective terms.” [32] To meet the Safety Act's requirement that standards be “practicable,” NHTSA must consider several factors, including technological and economic feasibility.[33]
In IIJA, Congress required NHTSA to issue this ANPRM to update FMVSS No. 207. The statute further states that if the Secretary determines a final rule complies with the Safety Act, a rule shall be issued with a compliance date not later than 2 motor vehicle model years after the model year the rule goes into effect.[34] Under this requirement, NHTSA is required to issue a final rule only if it meets the requirements of the Safety Act, namely that it is practicable, meets the need for safety, and is objective. In determining whether to proceed with the rulemaking, NHTSA must also consider all of the factors set forth in 49 U.S.C. 30111(b).
B. Regulatory History of FMVSS No. 207 and FMVSS No. 202, and Associated Research/Analyses
1. 1963—SAE Recommended Practice for Seats
The basis of the current FMVSS No. 207 standard is a recommended practice established by SAE International on November 1, 1963: SAE J879—Passenger Car Front Seat and Seat Adjuster. SAE J879 established uniform test procedures and minimum performance requirements for motor vehicle seats and seat adjusters.
J879 defined two test procedures. The first procedure, “Simulated Occupant Loading,” tested rearward seat back strength. It required a seat back to withstand a rearward moment of 480 Nm (4,250 in-lb) that was generated via a static load applied to the uppermost cross member of the seat back frame. However, this moment was calculated “about the rear attachments of the seat frame to the seat adjusters.” The July 1, 1968, revision to J879, J879B—Motor Vehicle Seating Systems, modified the moment to 373 Nm (3,300 in-lb) measured about the H-point, and the direction of the force was specified to be perpendicular to the seat back frame angle. The other procedure, “Simulated Inertial Loading,” established a 20 g minimum strength requirement for horizontal inertial seat loadings, applied in both the forward and rearward direction. This specification was designed to ensure that seat anchorages were strengthened to the point where the seats would remain attached to the vehicle body structure (typically the floor), preventing their inertia from releasing them and creating a ram-like action within the passenger compartment. During these tests, the seat back is braced to the seat base to isolate the seat attachment to the vehicle.
2. 1967—Publication of FMVSS No. 207, Seating Systems
In February 1967, FMVSS No. 207 was enacted, and it went into force beginning with MY 1969 passenger cars.[35] It was later extended to multipurpose vehicles, trucks, and buses in 1972.[36]
FMVSS No. 207 mostly mirrored the 1963 version of SAE J879. However, the minimum rearward moment requirement was set at 373 Nm (3,300 in-lb) as measured about the H-point.[37] Additionally, provisions were added for seats that folded forward to allow access to rear seats and to assure that seats had a positive restraining device (latch) to prevent them from swinging forward during a frontal crash. This prevented adverse inertial forces by a flailing seat back to the back of an occupant as they pitched forward during a frontal collision. The additional requirement also helped protect unrestrained rear seat occupants during frontal crashes or a hard breaking event who might otherwise get thrown over a pitched-forward seat back and could suffer injuries due to head impacts with the windshield or dash panel.
The new provision required the latch (and, hence, the seat back itself) to withstand a forward load of 20 times the weight of the seat back. The load was applied to the seat back at its center of gravity. There was a concurrent revision to SAE J879 in July 1968. SAE also changed the moment value and its reference point in J879 to be consistent with FMVSS No. 207. However, the SAE requirement applied the force generating the moment in a direction perpendicular to the seat back instead of horizontally (see Figure III.1). The result of this change was that a slightly higher force must be applied in FMVSS No. 207 to achieve the same moment level.[38] Since then, the requirements of FMVSS No. 207 and SAE J879B have not changed.
3. 1968—Publication of FMVSS No. 202, “Head Restraints”
In 1968, NHTSA issued FMVSS No. 202, “Head restraints,” requiring head restraints on cars manufactured after January 1, 1969.[39] The standard specified that the head restraint must sustain an 890 N (200 lb-f) rearward load applied 65 mm (2.5 in) below the top of the head restraint, while deflecting less than four inches (102 mm) and without a seat back failure. The standard also specified that the top of the head restraint must be at least 700 mm (27.5 in) above the H-point as measured along the torso reference line of the J826 manikin.[40] This effectively placed a 565 Nm (5,000 in-lb) moment minimum strength requirement on the seat back while also placing a lower bound on seat back stiffness because this moment must be achieved within a specified amount of deflection. Thus, between FMVSS Nos. 202 and 207, all requirements for seat back strength were set forth through static loads.
4. 1969—Report on Seat Safety Studies at ITTE
Following the issuance of FMVSS No. 207, Derwyn Severy, a principal investigator at the Institute of Transportation and Traffic Engineering (ITTE) at UCLA, published a paper [41] at the 13th Stapp Car Crash Conference advocating safer seat designs (“Stapp paper”). The ITTE had been conducting field investigations and crash tests throughout the 1960s as they worked to develop design concepts for vehicle seats.
The 1969 Stapp paper provided the basis for several seat design recommendations. Included were recommendations to increase the seat back strength requirement to 11,300 Nm (100,000 in-lb) and limit the seat back rotation to 10 degrees in a quasi-static test. According to Severy, this load level was consistent with collision-induced forces caused by the seat inertial forces augmented by a 50th percentile male occupant in a 30 g rear-end crash.
In 1976, Severy published a follow-on paper on seat design.[42] In it, he offered his observations on safety improvements in production seats brought about by the 1968 standard: “that laboratory tests established that production seats from cars large and small, foreign and domestic, and from vehicles 30 years old to new, have seat back strengths remarkably alike and that substantially exceed the required FMVSS No. 207 criteria.” Severy additionally stated that production seats were incapable of effectively resisting motorist inertial forces for any but light impact exposures without experiencing excessive yield and/or component separation.
5. 1974—Notice of Proposed Rulemaking (NPRM) To Revise FMVSS No. 207
In February 1974, Carl Nash of the Public Interest Research Group petitioned NHTSA to implement a dynamic requirement for seat backs. He asked NHTSA to add a rear impact test into FMVSS No. 208, “Occupant crash protection,” with acceptance criteria based on head rotation of a seated crash test dummy. Nash also called on NHTSA to consolidate FMVSS No. 202 with FMVSS No. 207 because of the close relationship between head restraints and seats in mitigating injuries in rear impacts.
In March 1974, NHTSA published an NPRM that included proposed seat back requirements that essentially mirrored Nash's request.[43] However, instead of amending FMVSS No. 208, NHTSA proposed to add the dynamic barrier test to a new, revised version of FMVSS No. 207. The test was to be conducted using the same moving barrier apparatus as that of the FMVSS No. 301 rear impact test for fuel system integrity, which had been proposed a year earlier.[44] Although a seated dummy was specified, NHTSA did not propose any requirements based on dummy head rotation as requested by Nash. Instead, NHTSA proposed a maximum seat back rotation of 45 degrees. The proposal also integrated the requirements of FMVSS No. 202 into a single, consolidated standard.
To support a decision for a final rule, NHTSA contracted with the University of New Mexico to conduct rear impact tests. Sled tests were run on yielding vs. rigid seat backs using post-mortem human subjects (PMHS).[45] At the time, NHTSA was concurrently investigating whether to revise FMVSS No. 202 to better mitigate the effects of whiplash. In consideration of this, rigid and yielding seats were tested with and without a head restraint. Sled tests were run by simulating a crash in which a stationary vehicle is struck from the rear by another vehicle having the same mass and travelling at a speed of 51 km/h (32 mph). The investigators observed that with no head restraint, rigid seats produced higher whiplash effects than yielding seats in low-speed rear impacts. Also, ramping was exacerbated in rigid seats with no head restraint. Thus, the results were deemed to be inconclusive as to whether yielding seats or rigid seats reduced the risk of injury. In addition to the work at the University of New Mexico, other basic research was being conducted on the more general topic of human injury tolerance to rearward forces and the biofidelity of the neck response of test dummies in rear impacts.[46 47] It is noteworthy that NHTSA commissions another study in 1974 on the safety of occupants of large school buses (school buses with gross vehicle weight rating (GVWR) greater than 4,536 kilogram (kg) (10,000 pounds (lb))) prior to issuance of FMVSS No. 222.[48] Following this study, NHTSA developed the concept of seating compartmentalization for school buses, which led to the following conclusion regarding the seating system: “The seats and restraining barriers must be strong enough to maintain their integrity in a crash yet flexible enough to be capable of deflecting in a manner which absorbs the energy of the occupant.” [49] At least in the context of larger school buses, NHTSA found there was a benefit to yielding seats that maintain structural integrity in order to maintain occupant compartmentalization when occupants were not protected by seat belts. Based on this conclusion, NHTSA developed a force-deflection requirement for the forward and rearward directions for large school bus seat backs.[50] The rearward requirement protects occupants in a rear collision, analogous to the rear impact issue discussed in this document.[51]
6. 1978—NHTSA Publishes a Request for Comment on Rulemaking Priorities
On March 16, 1978, NHTSA published a Request for Comments on the agency's plan to prioritize ongoing rulemaking efforts.[52] In establishing priorities for the plan, NHTSA stated that limited resources needed to be focused on rules with the largest safety benefits. It identified the 1974 proposal to require stiffer seats as one of several open rulemakings with low priority and proposed to terminate it. In 1979, when the plan was issued, the 1974 proposal was terminated.[53] No public comments were received in response to the request for comments.
Over the next several years, NHTSA continued to investigate the safety of occupants in rear impacts. Beginning in 1979, NHTSA conducted over 30 full-scale rear-impact crash tests on vehicles with instrumented dummies seated in the front seats. The FMVSS No. 301 barrier was driven into the stationary vehicles at speeds ranging from 48-56 km/h (30 to 35 mph). These rear impact crash tests are catalogued online.[54]
7. 1989—NHTSA Receives Petitions for Rulemaking on Revisions to FMVSS No. 207
In 1989, Kenneth J. Saczalski and Alan Cantor submitted their first petitions for rulemaking on this subject to NHTSA.[55 56] Saczalski sought an increase in the seat back moment requirement in FMVSS No. 207 from 373 Nm (3,300 in-lb) to 6,330 Nm (56,000 in-lb),a factor of 17 increase. The aim was to reduce the incidence of injuries due to ramping and ejection in rear-end crashes. On July 24, 1989, NHTSA notified Saczalski that his petition was granted.
Cantor's 1989 petition asked NHTSA to amend FMVSS No. 207 to eliminate occupant ramping during a rear impact. Cantor did not provide a standardized test procedure to measure and assess ramping, nor did he describe a practicable countermeasure that could prevent ramping. Nonetheless, on February 28, 1990, NHTSA notified Cantor that his petition was granted.
After granting these petitions, NHTSA published another request for comments (1989 RFC) on the need for amending the seat back performance requirement in FMVSS No. 207 and opened a docket to receive comments on the petitions and pertinent issues.[57] In his comments submitted to this docket, Saczalski provided additional recommendations.[58] He asked NHTSA to also include a dynamic rear impact crash test using the FMVSS No. 301 barrier and a 95th percentile male dummy in the seat.
Most comments from the automotive industry on the 1989 Saczalski and Cantor petitions opposed any new seat back stiffness requirements. They argued that real-world crash data did not indicate that a safety-related problem existed. General Motors, for example, cited its own field data to conclude that any benefits associated with seat standard changes for rear impact protection were very limited.[59] Ford cited a study of real-world crashes to conclude that a safety need did not exist.[60] The authors of that analysis had also reviewed test data from prior studies (including those of Severy, et al). They concluded that rigid seat backs would probably exacerbate injuries because yielding seats absorb energy safely as they deform, thus reducing injurious forces borne by the occupant, including whiplash-causing forces. Occupant rebound from a rear impact and a subsequent hard thrust forward was also cited as a negative effect of rigid seats. Furthermore, a follow-up study by two of the same authors concluded that ramping is more likely to occur in a rigid seat regardless of whether a seat belt is used or a head restraint is in place.[61] On the other hand, Mercedes-Benz supported an upgrade to FMVSS No. 207.[62] It noted that seats in Mercedes vehicles were specifically designed to reduce the danger to front and rear occupants during rear impacts as a result of excessive rearward seat back deformation and the resultant interaction between occupants.
At the time, NHTSA commissioned a study on injury incidence to support a rulemaking decision.[63] This analyzed the problem using NASS real-world crash data. The study confirmed that seat back yield in severe rear crashes does occur.[64] Severe crashes were found to be infrequent, however, amounting to approximately 5% of all rear impacts. The study also showed that impacts with components in the rear seat compartment and ejections are a relatively small portion of the injuries. Injuries due to occupant impacts to components in the rear seat compartment accounted for 2.8% (unrestrained occupant) and 0.1% (restrained occupant) of the most severe injury to front seated occupants in rear impacts, and only 3.2% of all harm to unrestrained occupants in rear impacts involved occupant ejection.
The study also concluded that current seat designs provided reasonable safety in rear-end crashes, and that seat belts are effective in reducing injuries. The report suggested that new head restraint designs offered the best possibility to mitigate the largest portion of injuries in rear-end crashes.
Additionally, Transport Canada submitted a report to the docket of 23 case studies of real-world rear impacts, all of which involved vehicles that experienced seat back failures, and 11 of which resulted in occupant ejections.[65] Of the cases involving a rear seat passenger, four of the five rear passengers sustained injuries attributed to seat back failure of the front seat.
NHTSA provided a summation of the comments and reports in a 1992 summary report.[66] This document was placed in the docket for the safety plan discussed below. The report concluded that improving seating system performance may be more complex than simply increasing the strength of the seat back, and that a proper balance in seat back strength and compatible interaction with head restraints and seat belts must be obtained to optimize injury mitigation.
8. 1992-2000 NHTSA Publishes a Request for Comment on Possible Revisions to FMVSS No. 207, Grants Two Petitions and Conducts Research
In November 1992, the agency published another Request for Comment on more recent research findings and a proposed plan to address seat back performance.[67] At that time, the agency had refrained from upgrading FMVSS No. 207 until significant results from research were obtained, though the rulemaking action resulting from the 1989 petition grants was still open. The first document the agency placed in the docket was a report summarizing agency findings up to that point. The 1992 report stated that four categories of performance issues need to be addressed as part of potential future changes to FMVSS No. 207.[68] These four categories are:
(1) Seating system integrity: the ability of the seat and its anchorage to the vehicle to withstand crash forces without failure.
(2) Energy absorbing capability: the extent to which the seat and its attachment components absorb energy and the manner in which the seat and its attachment components release energy during rebound.
(3) Compatibility of a seat and its head restraint: The concern in this category is that any change in seat back energy absorbing capability could exacerbate head or neck injuries if the geometry and energy absorbing capability of the head restraint is not also changed.
(4) Seat belt restraint system: a seating system and its seat belt restraint system must complement each other to prevent injury.
Over the ensuing 10-year period, the agency conducted extensive physical testing of seat backs, performed computer modeling of seated occupants in rear impacts, and conducted dynamic testing of instrumented test dummies in vehicle seats. At the same time, NHTSA also assessed how new requirements for head restraints could mitigate whiplash injury in lower-speed rear-end crashes. The details of those efforts are outlined in several NHTSA reports provided in docket folder NHTSA-1998-4064 (document numbers 24-27, 31).
NHTSA also granted two more petitions related to seat back strength: King (March 1998) [69] and Hogan (December 1998).[70] King petitioned for a dynamic test using the FMVSS No. 301 rear impact test procedure. Hogan stated that conformance to the current regulation was being used in litigation as a defense for the performance of contemporary seat designs, and therefore asked NHTSA to “suspend” FMVSS No. 207 until such time that the standard could be improved.
In comments posted in dockets NHTSA-1996-1817 [71] and NHTSA-1998-4064,[72] most in the automobile industry argued that seat back deformation was protective to the occupant by absorbing some crash energy. However, there was recognition that better seat back performance requirements could improve occupant safety in rear impacts greater than 40 km/h (25 mph). Greater control of occupant kinematics in severe rear crashes was thought to enhance occupant safety, even for belted occupants, by controlling rearward deflection of the seat back. Further comments presented by the Advocates for Highway and Auto Safety expressed concern about the harm caused by bodily impact with vehicle structures and noted the importance of negating excessive seat back rotation, ramping, and occupant rebound. One individual consultant described the consultant's opinion regarding the deficiency of FMVSS No. 207 and the impact that the standard may have had on automotive seat designs from that time. Another consulting firm expressed concern about the level of deformation that occurs due to the force applied to seat backs of that time in rear impacts and its effect on the effectiveness of the restraint systems in higher severity rear impacts.
The comments and research at the time affirmed that the issues of seat back, head restraint, and belt retention were inextricably linked to overall occupant safety. For example, in studies such as the 1997 Prasad,[73] 1977 University of New Mexico study, and 1976 Severy study, the disbenefits of a rigid seat were particularly evident in seats with baseline head restraints.[74] In the 1997 Prasad study for example, the authors found that stiffer seats led to higher neck and lumbar spine loads in rear impact tests. One complicating factor from this period is that most of the laboratory tests were performed with Hybrid II or Hybrid III 50th percentile male (HIII-50M) dummies, which are seated dummies designed based on human indices measured in frontal crashes. The torso and pelvis of these dummies do not articulate well in rear impacts, and such articulation is needed to faithfully exhibit ramping. While a larger size ATD would more fully exercise a seat back in a rear impact, the additional use of a smaller ATD with female-specific characteristics may have provided a more comprehensive assessment of occupant kinematics and injury risk for different seat designs in these earlier studies. Comments posted in the docket also emphasized the rear impact protection points NHTSA made in the 1992 study, in particular the need for energy absorption of the seat back, while also recognizing that performance requirements may enhance rear impact protection.
9. 2004—NHTSA Issues Final Rule Upgrading FMVSS No. 202, Head Restraints
NHTSA's research on rear impact crashes and head restraints led the agency in January 2001, to address the problem of whiplash injuries by proposing to upgrade the head restraint standard, FMVSS No. 202.[75] At the time, the agency estimated that approximately 800,000 whiplash injuries occurred annually in all crash types, resulting in a total annual cost of $5.2 billion. Whiplashes in rear impacts were estimated to be about 270,000 annually.
After considering public comments on the proposal, NHTSA published the final rule on December 14, 2004.[76] It was estimated to reduce the number of whiplash injuries by about 17,000 per year. The revised standard imposed an increased head restraint height requirement such that all outboard front seat head restraints must be capable of adjusting to at least 800 mm (31.5 in) and not have an adjustment position below 750 mm (29.5 in). It also imposed a minimum backset [77] measurement that required the head restraint to be closer to the back of a seated occupant's head. The updated standard maintained the requirement for the head restraint to withstand a 200 lb-f or 890 N rearward force applied 65 mm (2.5 in) below its top, when adjusted to its highest position, which must be at least 800 mm. Thus, this imposes an effective rearward strength requirement on seat backs of 654 Nm (5,790 in-lb), where 654 = 890*(0.8-0.065). This is a factor of 1.75 greater than the rearward strength requirement of FMVSS No. 207.
10. 2004—NHTSA Terminates Rulemaking on FMVSS No. 207, Seating Systems
By the time NHTSA finalized the head restraint regulation in 2004, it was clear to the agency that additional research and data analyses were needed to allow a fully informed decision on any change to the seat back strength requirement in FMVSS No. 207. A year earlier, researchers at Johns Hopkins University Applied Physics Laboratory completed a study commissioned by NHTSA, which strongly suggested that seat back stiffness plays a role in whiplash injury risk in low-speed rear impacts.[78] The main finding was that the risk of whiplash injury cannot be related to a single design factor, such as head restraint height. The study concluded that altering the seat back design could have an effect on the occurrence of whiplash. Additional analyses were needed to assure that a NHTSA-imposed seat back requirement would not create a greater risk of whiplash. Since it was not clear when such analyses would be complete, on November 16, 2004, NHTSA terminated the FMVSS No. 207 rulemaking proceeding that had been open since 1989.[79] NHTSA was unable to fully establish that a need for a stronger seat back existed, establish a definitive link between injury reductions and potential new regulatory seat back requirements, or show that new requirements under consideration would not exacerbate risk of neck injuries due to whiplash, roof contacts, or rebound. However, NHTSA did not make a finding that an FMVSS No. 207 amendment was not warranted. Instead, NHTSA stated that further study is needed to make a definitive determination of the relative merits of different potential rulemaking approaches and that research on seat back issues would continue.
11. Further Regulatory Changes Since 2004
There have been two prominent regulatory changes regarding occupant safety in rear-end crashes that have been fully implemented since NHTSA terminated the rulemaking on FMVSS No. 207: a revision to FMVSS No. 202, and a revision to FMVSS No. 301, the fuel system integrity standard. FMVSS No. 202 is the standard focused on neck injury protection in rear impacts. Regarding FMVSS No. 301, while the stated purpose of the standard is to reduce incidence of fire and fuel ingestion incidents, it utilizes a test procedure that represents a relatively severe rear impact in the field and has been recommended by petitioners as a viable basis for an upgrade to FMVSS No. 207. Additionally, some researchers have reported that vehicles compliant with the updated FMVSS No. 301 have shown significant reduction in fatality risk in rear impact.[80] Therefore, as part of our analysis of the need for new seat back strength requirements, NHTSA considers the effects that these changes have had on seat performance and occupant injury risk in moderate-to-severe rear-end crashes.
(a) FMVSS No. 202a, “Head Restraints”
FMVSS No. 202a was issued in 2004 and applied an updated set of safety requirements for head restraints beginning with model year 2010.[81] Although the new requirements were not specifically intended to strengthen seat backs, the head restraint upgrade resulted in an increase in the minimum acceptable seat back strength.
FMVSS No. 202a requires a fully extended head restraint to withstand an 890 N (200 lb-f) rearward load. Although this load was not changed in FMVSS No. 202a, the minimum height of the head restraint was raised from 700 mm to 800 mm. Thus, the effective torque requirement on the seat back increased from about 565 Nm (5,000 in-lb) to 654 Nm (5,790 in-lb).[82]
FMVSS No. 202a also introduced a new optional dynamic test for head restraints. In the dynamic test, the entire vehicle is tested on a sled with a seated HIII-50M dummy and subjected to a 17.3 km/h (10.75 mph) rear impulse. The dummy's rearward head rotation with respect to its torso must be limited to 12 degrees for the dummy in all outboard designated seating positions. Though inertial forces of the occupant acting on the seat back in FMVSS No. 202a testing are much lower compared to those associated with an FMVSS No. 301 test pulse, FMVSS No. 202a's dynamic test may have potentially resulted in stronger seat back designs for those seats certified to this option because a stiffer seat back with an adequately positioned head restraint would capture the head motion before the limits are exceeded. Neither NHTSA nor, to our knowledge, the petitioners, however, have studied whether the upgrade to FMVSS No. 202a has resulted in injury reductions other than whiplash.
(b) Upgrade to FMVSS No. 301, Fuel System Integrity
On November 13, 2000, NHTSA proposed a more stringent rear impact offset test using a lighter deformable barrier.[83] A final rule was published on December 1, 2003, and the new requirements for the fuel systems were phased in during MYs 2007-2009.[84] Although the fuel containment requirements remained the same as the previous version of FMVSS No. 301, the crash test was generally more rigorous for most passenger cars. Vehicles that passed the new rear impact requirements were found to provide protection against crashes in which the impact produced a 33 to 50 percent higher ΔV (which corresponds to 110 percent more energy being dissipated in the crash) compared to the previous test.[85]
In a post-regulatory assessment, NHTSA compared the structure of pre- and post-standard vehicles. NHTSA observed substantial structure upgrades in the newer vehicles, which may mitigate intrusion of vehicle structures into the rear seat occupant compartment. For example, in the 2016 study, Viano and Parenteau found MY 2008 and onward FMVSS No. 301 compliant vehicles to have a 27.1-32.8% reduction in fatality risk in rear impacts compared to 1996-2001 MY vehicles. Two considerations limit the conclusions that can be drawn from this data. First, injury risk was estimated irrespective of post-crash fire. Thus, some of the injury risk reduction could be a reduction in the incidence of fire. Second, the authors noted that the changes in rear structures occurred while front seats were transitioning to higher retention designs, which may contribute to the reduction in fatality risk.
(c) NCAP
In 2007 NHTSA published a notice requesting comments on an agency report titled “The New Car Assessment Program (NCAP) Suggested Approaches for Future Program Enhancements.” [86] With regard to rear impact protection, NHTSA proposed that it could provide consumers with basic information on rear crashes such as safe driving behavior, proper adjustment of head restraints, real-world safety data by vehicle classes, and links to the Insurance Institute of Highway Safety (IIHS) rear impact test results. The agency further proposed that a dynamic rear impact test, which addresses those injuries not covered by the agency's current standards, could be investigated and incorporated into the ratings program. Several organizations and manufacturers recommended that NHTSA evaluate the effectiveness, cost, and safety benefits of a rear impact test before incorporating such a test into NCAP. Industry comments suggested that NHTSA should also evaluate the effectiveness of the FMVSS No. 202a update and that incorporating rear impact safety into NCAP would be better directed toward areas not fully addressed by the current regulation. Commentors suggested that NHTSA should study whiplash-type injuries and countermeasures and encourage public education on the proper adjustment of the head restraint. NHTSA concluded that a dynamic test would not be premature at that time since such an option existed in FMVSS No. 202a. However, NHTSA noted that the test dummy used by IIHS is not used for testing FMVSS compliance, and some of the injury criteria used for the assessment had not been correlated with real-world injury. Ultimately, the agency did not incorporate rear impact protection information into the NCAP program.
IV. Review of Additional Literature
NHTSA, industrial, academic, and non-profit researchers have conducted significant research into the rear impact protection of seat backs and head restraints, and research is ongoing. Researchers have investigated occupant dynamics in rear impacts, development of safer seats for the occupant in rear impacts, and occupant injury mechanisms in rear impacts.
A. Occupant Dynamics
Occupant dynamics and protection in rear collisions is a complex multivariable problem. The ideal safe seat for one occupant in a certain rear collision scenario may not be the ideal safe seat for another occupant or for a different scenario. For example, research suggests that females have a higher risk of whiplash injury compared to males and respond differently to a rear impact.[87 88 89 90] Additionally, other occupant characteristics, such as weight, can play a significant role in rear impact injury risk, as shown in the NASS-CDS case number 2011-49-57 noted by Viano and Parenteau.[91] This case outlines a rear collision with an estimated ΔV between 35 and 39 km/h (21.7 and 24.2 mph). The 141 kg (311 lb) driver of the rear impacted 2008 model passenger vehicle suffered critical head and neck injuries after decoupling from the rotated driver seat back and colliding with the rear seat back. The 68 kg (150 lb) right front passenger of the same struck vehicle, however, had no documented injury.[92] The injury severity suffered by the driver in this case is rare in rear impacts. Viano and Parenteau found passengers with injuries of MAIS 4 or greater severity, including fatalities, represented 0.08% of passengers with injury in rear collisions in MY 2008 and newer vehicles. A quantitative description of seat back response is complicated by the potential sensitivity of response to a range of initial conditions and external factors including head posture,[93] awareness,[94] seat belt use and seat geometry including initial seat back recline angle,[95] details of the crash pulse,[96 97] and specific occupant characteristics such as weight distribution. The initial posture and location of the occupant is also thought to influence injury risk. Many occupants in rear collisions are believed to be out-of-position ( e.g., seated off-center), and out-of-position occupants are thought to have a higher probability of injury in rear impacts than symmetrically or normal-positioned occupants.[98 99 100]
Some research suggests that limiting seat back rotation can have detrimental effects, particularly regarding neck injuries. In the 1997 Prasad study of real-world rear impacts, the authors concluded that a revision to severely limit seat back rotation would have detrimental effects. The study analyzed the 1980-94 NASS database to compare injury rates in pickup trucks with passenger vehicles in rear impacts. This allowed for comparison between yielding seat performance with the rotationally stiff seats of pickup trucks (stiffness is due to the small gap between seat and cab). A higher rate of occupant injury in rear collisions across all ΔVs was observed in pickup trucks. The authors inferred that rotationally rigid seats could have an increased rate of injury in rear impacts. The 1997 Prasad study further analyzed a series of sled tests to investigate the relationship between seat stiffness and anthropomorphic test device (ATD) kinematics for rear impact ΔV of 16, 24, and 40 km/h (9.9, 14.9, and 24.9 mph). After assessing the range of sampled speeds and ATD measurements, Prasad hypothesized that (all else being equal) stiffening of the baseline 1996 production seats can result in an overall increase in whiplash type injuries at low-to-moderate speeds and a greater potential for serious neck injury at higher speeds, in addition to other conclusions. This study, however, has limitations. Many of the pickups in the crash data analyzed may not have had head restraints because trucks were not required to have head restraints until MY 1993. Moreover, a rotationally rigid seat represents the extreme end of the debate around the seat strength set by FMVSS No. 207. While modern production seats are characterized by a seat strength many times the value set by FMVSS No. 207, these seats also display a degree of balance between high and low-speed rear impact protection and the characteristic of rearward rotation of the seat back.
Other research suggests that optimizing seat back design, including stiffness, can reduce injury risks in rear impact. In a 1996 study, Svensson, et al.[101] analyzed the influence of seat back properties on neck injury using the HIII ATD with a Rear Impact Dummy (RID)-neck in low-speed rear collision sled testing. The study found that it was possible to significantly reduce harmful head-neck motion of the ATD by optimizing the head-to-head restraint gap, seat back frame stiffness, and characteristics of the seat-back cushion.
A separate statistical analysis involving 20 years of the NASS database by Burnett [102] found that front seat occupants are significantly more protected in rear collisions compared to other crash directions, even for the most severe rear impacts where major seat yielding and occupant decoupling from the seat can occur. The study also conducted quasi-static mechanical testing and rear impact sled tests of seven production seats to investigate the correlation between mechanical parameters and ATD kinematics. The study found no significant correlation between the seat strength and any of the recorded ATD metrics, while seat stiffness and an energy absorption parameter were nonlinearly correlated with ATD metrics.
B. Rear Impact Protection Technology
This section discusses some seat designs intended to improve rear impact protection that have been incorporated over the years.
In 1998, a set of design guidelines was published by Volvo Cars and Autoliv, Inc. for seats that emphasized the importance of controlling an occupants' absolute and relative head and torso kinematics throughout the rear impact process, to protect against neck and other injuries.[103] The Volvo Cars' Whiplash Protection System (WHIPS) was introduced in 1998 and is built around these guidelines. In a significant rear collision, the first generation WHIPS seat back rotation point moves rearward and later transitions to rearward rotation. During seat back rotation, a mechanical linkage irreversibly absorbs rotational energy, so there is less energy directed into the occupant and rebound is reduced. The seat back will then continue to rotate and deflect rearward as a typical production seat. According to data reported by Volvo, the first generation WHIPS seat reduced soft tissue neck injury risk by 21% to 47% as compared to prior seats.[104]
Another technology for whiplash injury protection is active head restraints that was introduced by Saab in the late 1990s.[105] These systems aim to reduce the head restraint contact time by actively shifting the head restraint forward in a rear impact through a mechanical linkage in the seat structure activated when the seat occupant moves rearward into the seat. Data acquired by the NCAP program for MY2023 show that 21 vehicle models representing 4 percent of vehicle sales are reported as having active head restraints or provide the option. At least one automotive supplier is working on an electromechanical system that moves the head restraint up to 40 mm forward when a rear sensor in the vehicle anticipates a rear impact.[106]
In the early 1990s, General Motors (GM) Research and Development Center undertook an in-depth study of seat characteristics to improve occupant safety in rear impacts. In general, the GM seat design fostered movement of the pelvis rearward and into the lower portion of the seat back frame in a way that would preclude ramping and reduce the moment arm on the seat back. A key design component was to balance the stiffness of the seat resisting the rearward movement of the pelvis against the ability of the seat back frame to resist backward rotation. GM established their own quasi-static test for the purposes of assuring that a given seat met the design parameters. It was a destructive test that made use of a 50th percentile male dummy loaded rearward into the seat back through the lumbar joint. The dummy was free to move up, down, and sideways during rear loading. The test also allowed the seat back to rotate rearward and twist in a manner similar to what was observed in sled testing. Eventually, GM's seat design targets were published by SAE International.[107] The targets were derived from various measurements taken during their quasi-static test. The targets contained many more parameters than FMVSS No. 207's single requirement to withstand a 373 Nm (3,300 in-lb) moment (see table 1 for a list of the parameters). Notably, the GM parameters included a criterion that limited the seat stiffness to no more than 25 kN/m, while attempting to assure that the seat had sufficient energy absorbing properties. GM stressed that simply raising the FMVSS No. 207 moment beyond 373 Nm would not achieve a desirable seat design. According to GM, increasing only the seat back's stiffness would reduce the beneficial effects of yielding.
A seat design feature that was rare 25 years ago, but appears to be much more common in modern seats is a dual recliner system.[108 109] A dual recliner system places gear mechanisms controlling the static recline angle on both sides of the seat. This improvement significantly strengthened production seats and reduced longitudinal axis twisting.[110] The agency does not have an estimate of the current level of implementation of dual recliners and requests that commenters provide these data.
An IIHS study of contemporary production seats claims that a wide range of seating systems have achieved a balance between low-speed protection while maintaining structural integrity at higher speeds and occupant retention.[111] This study conducted rear impact sled testing on 26 modern production seats at a ΔV of 36.5 km/h (22.7 mph) using a 78 kg (172 lb) Hybrid III 50th percentile male dummy. The maximum dynamic seat back rotation ranged from 15° to 47° from the initial angle and the dummy was retained by all seat backs. During testing, the vertical displacements of the dummies was between 41 mm to 144 mm. The authors concluded that a majority of tested production seats provided adequate occupant retention at a ΔV of 36.5 km/h (22.7 mph), but with a range of performance metrics. Moreover, all 26 seats tested by IIHS had “Good” ratings for low-speed rear impact protection as determined by a separate IIHS test using the BioRID dummy at a ΔV of 16 km/h (10 mph).
C. Non-Contact Injuries
This section outlines a segment of the literature concerning non-contact neck and thorax injuries resulting from rear collisions.
1. Neck Injuries
The term whiplash has been used since the 1920s to describe various symptoms or signs of cervical spine injury in motor vehicle accidents. The first case series studies on motor vehicle whiplash injury were published in the early 1950s.[112] Later in the 1960s, studies were conducted on the mechanisms of whiplash injury.[113] These and related efforts developed the notion that the whiplash injury rate could be reduced by preventing hyperextension of the neck. The initial version of FMVSS No. 202 mandated head restraints as a countermeasure to this type of neck injury.[114] After the mandate was introduced, a statistical analysis of crash data sets found modest improvements in the whiplash injury rates.[115] A 1982 NHTSA report of rear impacts in passenger cars, for example, found that integral head restraints reduced whiplash injury risk by 17% while adjustable restraints reduced the risk by 10%.[116] A Swedish study found a similar 20% decrease in neck injuries as a result of the head restraint.[117] However, the persistence of frequent whiplash injury motivated later studies of cervical spine dynamics in rear collisions.
In 1995, the Quebec Task Force on Whiplash Associated Disorders categorized whiplash injuries into five grades, 0 to IV, in order of increasing severity. For convenience, we will continue to refer to whiplash associated disorders as whiplash injuries. The Quebec study determined that 90% of insurance claims fell within grades 0 and I where there was no clear pathology based on existing technology, but symptoms may include neck pain, headache, memory loss, jaw pain, hearing disturbance, and dizziness. Grades II and III include musculoskeletal and neurological signs; grade IV contains cervical fractures and dislocations. The most severe soft tissue whiplash type injury occurring in grade IV is typically characterized by disc herniation and is often accompanied by facet-joint hematoma, peripheral spinal nerve and spinal cord contusion or articular process fracture.[118] The findings of a study on very low velocity rear collisions [119] led the authors to conclude that a biomechanical “limit of harmlessness” for whiplash exists for rear collision ΔV between 10 to 15 km/h. The author goes on to explain that this is the speed range below which there were no anatomical signs of injury, but did not rule out “psychological injury.”
Basic research of rear collision neck kinematics indicate that neck and head dynamics occur through a complex process. The neck may experience compression, tension, shear, torsion, retraction, protraction, flexion, and extension to varying degrees and at different points in time. Studies on cervical spine kinematics in rear collisions by Svensson, et al.[120] and McConnell, et al.[121] in 1993, Geigl, et al.[122] in 1994 and Panjabi, et al.[123] in 1998 noted that the neck displayed an unnatural S-shaped curve in the early stages of the kinematics due to retraction, and Panjabi hypothesized that neck injury may occur before head contact with the head restraint. In a study by Feng, et al.,[124] the authors described early rear impact neck dynamics through a series of kinematic spinal processes. The authors noted that rear impact forces are at first distributed across the occupant's torso through the seat back and then are transmitted to the neck and head. These initial forces impose torso straightening and likely movement of the occupant's torso up the seat back. The authors hypothesize that axial compression is generated in the spinal column, which travels up the neck to the head. As the head moves upwards axial tension is then proposed to develop in the neck through disproportionate movement of the head and neck due to a constrained torso. As these first actions evolve the head lag phenomenon (also described in an earlier 1976 study [125] ) or retraction develops through a delay between the forward motion of an occupant's torso and head. Retraction leads to shear in the cervical column and curvature of the neck is reduced. These theorized actions occur before the head contacts the head restraint.
2. Thorax Injuries in High-Speed Rear Impacts
A recent NHTSA research study was conducted with 14 PMHS tests in rear facing seats in frontal collisions at a ΔV of 56 km/h for different recline angles and seat types to investigate thorax injuries.[126] The structure supporting the seat back was rigidized to avoid unpredictable permanent deformations of the seat during the event. The goal of the study was to examine non-standard seating configuration for vehicles with automated driving systems (ADS) with reclined rear-facing seats in a frontal collision. It may also, however, provide some insight into rear impact dynamics because the loading is rearward with respect to the seat back orientation. Additionally, the 56 km/h ΔV test is very severe for a rear impact. The CISS data reported in section II.B indicates this speed represents more than 95% of all towaway rear impacts. The authors found that rib fractures occurred in the PMHSs due to a complex combination of chest compression and expansion with upward shear loading. The majority of rib fractures occurred after peak chest compression when the abdominal contents shifted rearward and upward into the thorax due to the ramping motion of the PMHS, which created a combined loading (compression/tension and shear) to the thorax. Similar magnitudes of rib strains were observed regardless of seat types, while strain modes varied according to recline angle and seat type. Fewer injuries were seen with a more upright 25-degree seat back, compared to a more typical initial seat angle of 45-degree seat back.
D. Summary
While progress has been made in understanding rear impact injuries, the literature continues to point toward the need for a greater understanding before conclusions can be drawn about the exact mechanisms of injury and the risk factors involved, particularly in regards to whiplash.[127] Likewise, important safety improvements have been made in production seats over the last 50 years and a greater understanding of the relationship between seat back characteristics and injury has been achieved, but questions remain with respect to precisely quantifying protective characteristics. The continued uncertainty around how best to protect occupants as well as the varied approaches and developments in rear impact technology suggests that, as NHTSA considers amendments to FMVSS Nos. 207 and 202a, there is value in preserving industry flexibility in seat back and head restraint design and strength parameters to allow further research into and development of these systems.
V. Petitions for Rulemaking at Issue in This Document
A. Statutory and Regulatory Background
Under 5 U.S.C. 553(e), 49 U.S.C. 30162(a)(1) and 49 CFR part 552, interested persons can petition NHTSA to initiate a rulemaking proceeding. Upon receipt of a properly filed petition, the agency conducts a technical review of the petition, material submitted with the petition, and any additional information.[128] After conducting the technical review, NHTSA determines whether to grant or deny the petition.[129] The Safety Act states that all FMVSS requirements must be practicable, meet the need for motor vehicle safety, and be stated in objective terms.[130] Accordingly, NHTSA will initiate a rulemaking only if the agency believes that the proposed rule would meet these criteria. If a petition is granted, a rulemaking proceeding is promptly initiated in accordance with statute and NHTSA procedures. A grant of a petition and a commencement of a rulemaking proceeding do not, however, signify that the rule in question will be issued. That decision is made on the basis of all available information developed in the course of the rulemaking proceeding, in accordance with statutory criteria.[131] If a petition under this section is denied, the reasons for the denial are published in the Federal Register .[132]
B. Petition of Kenneth J. Saczalski
On October 28, 2014, Kenneth J. Saczalski of ERST petitioned NHTSA to amend FMVSS Nos. 207 (Seating systems), 213 (child restraint systems), and 301 (Fuel system integrity). Saczalski requested that NHTSA increase the static strength requirement for seat backs by a factor of six and implement a new dynamic requirement. The dynamic requirement would assess the seat back of a vehicle by performing a rear impact crash test with a 50th percentile male ATD positioned in the seat. The petition also suggested adding a rear impact requirement to FMVSS No. 213, “Child restraint systems,” and implementing a new requirement for rear seats that would resist the forces of loose cargo that may be stowed behind the rear seats.
1. FMVSS No. 207, Seating Systems
Saczalski seeks an amendment to FMVSS No. 207, S4.2(d) to increase the rearward force that occupant seats must withstand from a 373 Nm (3,300 in-lb) moment measured about the H-point to a 2,260 Nm (20,000 in-lb) moment measured from the pivot intersection of the seat back structure and the seat cushion frame.[133] While this ostensibly represents an increase by a factor of six, because FMVSS No. 202a effectively requires seat backs to withstand a 654 Nm (5,790 in-lb) moment, this would only increase the performance requirement by a factor of 3.5 above current requirements, if measured about the H-point. The actual factors would be closer to a factor of 5.4 above the required FMVSS No. 207 moment and 3.1 above the FMVSS No. 202a requirement, depending on the relative position of the seat pivot with respect to the H-point.[134]
Saczalski also made a more general request that FMVSS No. 207 seat strength testing be conducted “to ultimate strength levels” that establish a seat's capacity to withstand crash forces. According to Saczalski, testing must be repeated to examine strength variations relating to adjustable seat components, such as height adjusters. Saczalski does not, however, provide a specific set of performance requirements or tests that he asserts should be conducted. Saczalski also requested that NHTSA add a requirement that seats not experience a “sudden load collapse” ( i.e., a failure of structural components that causes the occupant support loading to suddenly drop off) of 400 pounds force or greater within a short span of rearward deformation. According to Saczalski, this testing should be done using a “torso body-block” device that replicates the upper body weight of a 95th percentile male.
2. Use of FMVSS No. 301, “Fuel System Integrity,” To Test Seats
Saczalski petitioned NHTSA to implement a new seat back requirement using the dynamic rear-end crash test prescribed in the latest revision of the fuel system integrity test described in FMVSS No. 301. In this test, a stationary vehicle is struck in the rear by a 1,368 kg (3,015 lb) deformable barrier travelling at 80 km/h (50 mph). The barrier overlaps the rear end of the vehicle by 70%.
Saczalski asserted that a dynamic, full vehicle test is needed in addition to the static requirements discussed above. The main purpose of such a test would be to fully assess the safety of children in rear seats who may be exposed to collapsing front seat backs. Saczalski cites in his petition a 2008 study by Children's Hospital of Philadelphia (CHoP).[135] The study examined risk levels through an epidemiological study of real-world crashes, and found that in a rear-end crash, children seated directly behind a seat back that yielded exhibited about twice the risk of injury as children seated behind a seat back that did not yield. Saczalski has asked for a dynamic test to be run with Hybrid III 95th percentile male dummies (HIII-95M) in the front seats with 12-month-old dummies seated directly behind in forward-facing child restraints.[136] He recommends a pass/fail limit on front seat back rotation of no more than 25 degrees rearward from its initial seat back orientation. He also recommends that NHTSA impose pass/fail requirements based on dummy measurements within the head, neck, chest, and extremities. This would apply to the HIII-95M and the 12-month-old dummies. Saczalski recommends pass/fail requirements for both dummies equivalent to “their respective NHTSA injury reference levels for the head, neck, chest, and extremities.” [137]
Saczalski also suggested that the test be run with 20 kg (44 lb) simulated luggage cases in the trunk area, which he stated could push the rear seat forward. According to Saczalski, such a requirement will guard against injuries due to the intrusion of a rear seat occupied by a child into a yielding front seat back.
3. FMVSS No. 213, Child Restraint Seats
Saczalski asked NHTSA to include a rear impact requirement for child restraint systems within FMVSS No. 213, which does not contain such requirements. He suggested using the same test and performance criteria as the European standard for child restraint systems, United Nations Economic Commission for Europe Regulation 44 (ECE R.44),[138] but run at a higher test speed of 40 km/h.[139] The ECE standard contains requirements for various sized child dummies subjected to a 30 km/h rear impact. Like FMVSS No. 213, the European standard also includes requirements for a frontal impact, but those are not discussed in Saczalski's petition.
C. Petition of Alan Cantor
In a letter dated September 28, 2015, Alan Cantor of ARCCA petitioned NHTSA to revise FMVSS No. 207 by implementing new requirements for seat back strength involving a crash test with an ATD. He also requested that NHTSA reinstate a provision to FMVSS No. 209, “Seat belt assemblies,” that he states would prevent occupant injuries in rear impacts.
1. Use of FMVSS No. 301, “Fuel System Integrity,” To Upgrade FMVSS No. 207
Cantor requested a dynamic test to assess seat back loading by occupants of different sizes. He envisioned the use of the current FMVSS No. 301 procedure with Hybrid III 50th Percentile male dummies (HIII-50M). Additionally, Cantor requested that a test be performed at oblique impact angles to assess the potential of excessive seat back twisting that Cantor stated could facilitate rearward ramping and an out-of-position orientation of the occupant in the seat during subsequent impacts. A full vehicle test was also envisioned, but alternatively Cantor suggested that a sled test could be run using an impulse equivalent to that produced by the dynamic procedure. Cantor did not request a change to the static requirements of FMVSS No. 207, nor did he call for the use of rear seated child dummies in the dynamic, full vehicle test. Under Cantor's rationale, the test with the HIII-50M dummies would serve as the basis for a new set of FMVSS requirements. The requirements would apply to front seats as well as rear “bucket” seats, such as those within minivans, that he suggests may also have a propensity to collapse.
2. Rearward Rotation Limit and Structural Symmetry Requirement
Cantor recommended a pass/fail limit for rearward seat back rotation of no more than 15 degrees from its initial seat back orientation (measured in real-time during the test). For the oblique impacts, there would be a requirement that the differential rearward deflection of the seat back is no more than 10 degrees between the left and right sides. According to Cantor, this will assure structural symmetry of the seat to prevent excess twisting of the seat under load, which can lead to ramping or out-of-position orientation of an occupant if subsequent impacts occur.
3. Additional Dynamic Testing and NCAP Implementation
Cantor also requested another dynamic test to assess seat back loading to be performed with a Hybrid III 95th male dummy (HIII-95M) and to incorporate results into the NCAP star rating for the vehicle. This test would be performed in a manner similar to the current FMVSS No. 301 procedure, but at an impact speed of the barrier that is 8 km/h (5 mph) faster than the current FMVSS No. 301 speed. He argues that it would serve to inform consumers on whether a given vehicle seat back has the propensity to collapse. Cantor states it would also provide incentive to manufacturers to develop enhancements to rear impact crash protection.
Cantor recommended the same pass/fail limit for rearward seat back rotation for the NCAP tests as he recommended for the FMVSS No. 301 impacts. Cantor did not specify how the results would be factored into the NCAP rating.
4. FMVSS No. 209, Seat Belt Assemblies
Cantor requested that NHTSA restore S4.1(b), which NHTSA deleted in a final rule published in 1999.[140] This provision required the lap belt portion of the seat belt be designed to remain on the pelvis under all crash conditions. Cantor states that restoring S4.1(b) would assure that vehicles will be equipped with seat belt technologies that prevent ramping in rear impact crashes.
D. NHTSA's Analysis of Saczalski and Cantor Petitions
NHTSA is denying in part the Saczalski and Cantor petitions as they pertain to the following recommendations: Cantor's requested amendments to NCAP and request to restore anti-ramping language to FMVSS No. 209, and Saczalski's requests to add a rear impact test to FMVSS No. 213 and a cargo test requirement to FMVSS No. 207. As part of this rulemaking effort to update FMVSS No. 207 and to facilitate informed comment, NHTSA is granting the petitions in part with regard to updating the strength requirement in FMVSS No. 207, the structural symmetry requirement requested by Cantor, and the possible development of new test procedures for seat back strength under FMVSS No. 207. NHTSA notes that, at this time, insufficient information has been provided to support the petitioners' suggested specific strength levels or test designs, but NHTSA seeks comment on this issue. The remainder of this section provides NHTSA's opinions on the recommendations in the petitions to provide context and information to support informed comment on an update to FMVSS No. 207. Later in this document, we discuss NHTSA's current thinking on an integrated and unified approach to rear impact protection and seeks comment on that approach.
1. Analysis of Data and Research Provided by Cantor and Saczalski Regarding Safety Need
In the past, NHTSA and petitioners on this topic have not been able to demonstrate that a safety need exists regarding the seat back strength requirement in FMVSS No. 207.[141] In their petitions, Saczalski and Cantor both implied that factors related to child safety have given rise to a new safety need for stronger seat backs. NHTSA acknowledges that there is evidence that, in some crash scenarios, seat back deformation or rearward movement due to component failure can lead to injury, but NHTSA believes that the petitioners have not provided sufficient supporting data to demonstrate a worsening safety need related to seat back strength compared to NHTSA's past determination. NHTSA discusses the materials provided by petitioners below and seeks comment on this question.
In support of his petition, Saczalski references the CHoP study. NHTSA agrees with Saczalski that the 2008 CHoP study is useful for understanding the levels of risk to which children in rear seats are exposed, but the CHoP study did not determine that this risk was associated with front seat back strength. The information submitted by petitioners did not provide new or pertinent information to build upon the CHoP study or further demonstrate a safety need.
Saczalski provided NHTSA with his own publications, including one from the 2014 annual meeting of the International Federation of Automotive Engineering Societies (FISITA).[142] This paper described 13 cases of infant fatalities in rear-end crashes in which the infant was seated behind an occupied front seat. However, as with the CHoP study, Saczalski's paper did not provide additional insight on whether the fatalities were associated with front seat back strength. Moreover, because most of the fatalities occurred in vehicles that were built prior to MY 2000, the cases he cites may not reflect the lower level of risk associated with new vehicles. Since then, improvements have been made to FMVSS Nos. 202a, 301, and other standards that may impact the conclusions reached in the CHoP study and Saczalski's paper. In addition, changes in manufacturer's design targets and the more frequent use of dual recliners may have resulted in seat designs that are generally stronger.
Saczalski also provided the results of several sled tests with crash test dummies, which he argues demonstrate that the seat back of a front-seated adult can collapse on a child sitting in the rear in a 48 km/h rear-end impact. While these tests may illustrate the potential consequences of seat back deformation or failure, they simply reinforce a finding of which NHTSA is already aware: that it is possible for some seat backs to yield in a severe rear-end impact in a way that could potentially injure occupants.
Finally, according to Saczalski, fatality counts within the Fatal Accident Reporting System (FARS) from 2001-2011 show that fatalities in infants (0-12 months) have doubled since 1990-2000, from which he infers a worsening safety need.
NHTSA believes that the conclusion Saczalski draws from this data is inaccurate. NHTSA has queried FARS for infant and adolescent fatalities where the child was known to be restrained in a rear seat, non-ejected, in a non-rollover, rear impact. Over the last 15 years captured in the study, the average fatality rate is 7.7 per year, ranging from 1 to 15 per year (See Figure V.1). There is a great deal of scatter and no clear fatality trend over time. If the data are expanded to all children up to an age of 5, the average fatality rate is 31.9 per year, ranging from 22 to 60 (See Figure V.2). Again, there is no clear trend in the data. The data for the 0-5-year-olds have less scatter than that for the 0-12-month-olds. This latest data is not supportive of a claim that there is a fatality risk that continues to increase. NHTSA notes that these data provide an estimate of all-cause mortality and therefore provide no insights into whether front row seat performance contributed to the child's death.
2. Rear Structure Intrusion
Saczalski states in his petition that there are phenomena other than front seat back failure and ramping that create risk to children in rear seats. He notes that rear-seated children in rear-end collisions are often injured by poorly designed rear structures that push children forward into the front seat back. He supports this claim using a 2008 study of NASS-CDS data, which looked at the risk to children seriously injured in rear impacts and indicated that injury caused by intrusion from the rear seating area is a larger problem than deforming front seat.[143] NHTSA appreciates the analysis done by Saczalski and agrees that there is evidence to support a finding that there is a safety risk to children in the rear seat in a rear impact crash. NHTSA also agrees that this risk involves more factors than just front seat back collapse, such as rear structure intrusion. NHTSA seeks comment on the significance of the intrusion issue in the overall context of rear impacts and whether a practicable solution to this issue exists. NHTSA notes that the 2006 revision to FMVSS No. 301, Fuel system integrity, which would not have been in place for the model years of the vehicles Saczalski studied, may have induced changes to rear vehicle structures that mitigated the intrusion problem.
NHTSA wishes to emphasize that Saczalski and Cantor do not appear to have considered whether increasing the requirement for seat strength would have any unintended negative safety impacts. This document discusses at length the literature, such as the 1997 Prasad study, which suggest a possible association between significantly stiffer seats and increased incidence of whiplash and other non-contact injuries. NHTSA seeks comment on these potential negative safety impacts, which the agency believes is critical to understanding the overall safety problem in occupant protection in rear impact and whether changes to FMVSS No. 207 will meet a need for safety.
3. Cost and Practicability
Cantor argues in his petition that upgrading seat back strength would not impose a major cost on manufacturers, claiming that many modern vehicles have stronger seats compared to those in 1989 even in absence of a change to FMVSS No. 207. To support this claim, he cites his own testing, in which he claims to have studied newer vehicles using the FMVSS No. 207 procedure and found that they “tested out” somewhere between 2.5 to 10 times the current compliance level (373 Nm). Based on his own testing, he concludes that it would not be cost prohibitive for original equipment manufacturers that use less strong seats to increase seat back strength, and he argues that an upgrade to the standard is needed to assure all seat backs have a minimum strength.
NHTSA does not believe that Cantor's examples of actual seat back strength in the modern vehicles provide new or better data over what was known to NHTSA in 2004, when NHTSA terminated a rulemaking to increase seat back strength. The variance seen in Cantor's test results is consistent with that seen in the Severy data from the 1960s. It was also seen in data in a 1998 report prepared by NHTSA.[144]
NHTSA agrees that increasing seat back strength is technically feasible. Any rulemaking action to change the seat back strength requirement, however, must be practicable, meet the need for motor vehicle safety, and be stated in objective terms. As part of this analysis, a rulemaking action would assess whether this would be a cost-effective way to increase overall motor vehicle safety.
E. Assessment of the Specific Recommendations by Cantor and Saczalski
In this section, NHTSA presents its assessment of specific matters petitioned for by Cantor and Saczalski. The first section discusses the matters on which NHTSA is granting the petitions and initiating rulemaking and provides NHTSA's opinions on those specific petitioned-for issues to facilitate informed comment. The second section covers the issues on which NHTSA is denying in part and provides the reasons for denial as required in 49 CFR part 552.
1. Matters on Which NHTSA Is Granting the Petitions
(a) Amend FMVSS No. 207 To Increase Seat Back Moment Requirement and Alter Load Application Method
Saczalski asked NHTSA to raise the torque requirement about the seat back pivot to 2,260 Nm (20,000 in-lb). This would raise the current FMVSS No. 207 requirement of 373 Nm (3,300 in-lb) by a factor of about 5.4 and by a factor of about 3.1 above the FMVSS No. 202a requirement of 654 Nm (5,788 in-lb). In addition, Saczalski recommended that the load be applied through a “body block” representing a 95th percentile male, rather than to the upper member of the seat frame. NHTSA is granting the petition on the torque requirement and static test design issues in part, is initiating rulemaking to consider whether to upgrade FMVSS No. 207 on these topics and seeks comment on the analysis below.
Saczalski did not explain why a torque limit of 2,260 Nm was preferable to other limits that NHTSA has considered previously (See table V.1) and would not result in the potential safety harms discussed above. Furthermore, Saczalski does not provide a compelling reason why a body block test would be the most effective way to test rearward moment strength statically. NHTSA notes that Saczalski is also requesting a dynamic requirement, and he did not explain why amending the FMVSS to use a body block for the static test would be necessary if NHTSA were to accept his recommendation to incorporate a dynamic test with a more biofidelic dummy.
Table V.1—Past Recommendations for Revising the Quasi-Static Seat Back Torque Requirement in FMVSS No. 207
Test reference Current standard Recommendations FMVSS No. 207 (since 1968) Severy (1969) NHTSA (1974 NPRM) Saczalski (1989 petition) Viano 1 (2003) Saczalski (2014 petition) H-point moment, min 373 Nm (3,300 in-lb) 11,300 Nm (100,000 in-lb) 373 Nm (3,300 in-lb) 6327 Nm (56,000 in-lb) 1700 Nm (15,000 in-lb) 2260 Nm (20,000 in-lb). Seat back requirement “withstand” torque “withstand” torque specifics given below “withstand” torque. Seat back rotation, max 10 deg 40 deg Load drop limit, max 2000 N over 10° rot 1780 N “sudden”. Load application upper member of seat back frame upper member of seat back frame upper member of seat back frame upper member of seat back frame thru HIII-50M lower torso thru HIII-95M body block. Seat stiffness, max 25 kN/m Frame compliance, max 2.0 deg/kN Load limit, min 7.7 kN Seat twist, max 15 deg Dummy H-point upward displ., max (design target only) 50 mm 1 Viano's quasi-static test equipment and procedure represents more of an alternate test method than a simple revision to FMVSS No. 207. Details are described in Viano (2003), “Resolving the debate between rigid (stiff) and yielding seats: seat performance criteria for rear crash safety,” cited earlier. Saczalski also suggested that NHTSA impose a requirement so that, when tested to failure, there is no sudden drop in load of 1,780 N (400 lb-f) or greater within a short span. NHTSA is also granting the petition on this issue in part. NHTSA is aware of others who have recommended similar changes in the past to assure a gradual deformation of seat back components. NHTSA notes that Saczalski did not suggest an objective and practicable test procedure. Depending on how a test is carried out, a sudden load drop in a quasi-static test may not necessarily indicate an unsafe design. Even a drop to zero is not necessarily problematic if a slight perturbation in backward movement brings the load back up. NHTSA seeks comment on this requirement. What safety benefits could be obtained from such a requirement? Is there a practicable and objective test procedure that can be developed?
(b) Structural Symmetry
To assure structural symmetry of the seat, Cantor petitioned for a pass/fail limit for rearward seat back rotation of no more than 15 degrees from its initial seat back orientation (measured in real-time during the test) and 10 degrees of differential rearward deflection between the left and right sides for oblique impacts. NHTSA is granting in part on this issue and seeks comment. In particular, does the increased prevalence of dual recliners in the fleet remove any safety benefits that may be gained from a structural symmetry requirement? If not, what test procedures and anti-twisting standards should NHTSA consider and why? NHTSA notes that Cantor does not provide data or evidence supporting his proposed pass/fail limit or deflection amounts proposed.
(c) Dynamic Rear Impact Test Design
Both Saczalski and Cantor petitioned NHTSA to add a new dynamic crash test to FMVSS No. 207, which would test seat back performance using a 1,368 kg (3,015 lb) deformable barrier that strikes the rear of the vehicle at 80 km/h.[145] NHTSA is granting the petitions in part on this issue and seeks comment on the analysis below. NHTSA has previously considered, in the 1974 NPRM, adding a new dynamic requirement of the type recommended by Saczalski and Cantor. Table V.2 shows the various dynamic rear impact tests that have been proposed and considered in the past.
Table V.2—Past Recommendations for a Dynamic Seat Back Strength Requirement
Nash 1974 NPRM 1974 Saczalski 1989 1 Cantor 1999 2 Viano 2002 Saczalski 2015 4 Cantor 2015 Test type FMVSS No. 301 (1974) FMVSS No. 301 (1974) FMVSS No. 301 (1974) FMVSS No. 301 (1974) Sled test FMVSS No. 301 (2003) FMVSS No. 301 (2003). Impactor speed 3 48 km/h 48 km/h 48 km/h 48 km/h 30-36 km/h3 80 km/h 80 km/h. Barrier specs 1814 kg rigid 1814 kg rigid 1814 kg rigid 1814 kg rigid 1368 kg deformable 1368 kg deformable. Impact angle +/− 30 deg 0 deg 0 deg 0 deg 0 deg 0 deg +/− 30 deg. Impact overlap 100% 100% 100% 100% 100% 70% 70%. Dummy size HII-50M HII-50M HIII-95M 50M2 HIII-50M HIII-95M HIII-50M. Rear seat dummy CRABI-12M in FFCS Seat back rotation, max No fail 40 deg 40 deg 15 deg 35 deg 25 deg 15 deg. Seat back twist, max 8 deg 10 deg. Head, HIC unspecified value CRABI 390 | HIII 700 Head/neck extension 45 deg 45 deg n/a 10 deg. Neck moment 45 deg unspecified value 20 Nm CRABI 17 Nm | HIII 179 Nm Neck x-displacement 60 mm n/a Neck y-displacement 30 mm n/a Chest deflection CRABI 30 mm | HIII 70 mm Femur load CRABI n/a | HIII 12.7 kN 1 Contained within Saczalski's comments to NHTSA's 1989 Request for Comments. SeeRegulations.gov, Docket Document No. NHTSA-1996-1817-0024. 2 Contained within Cantor's presentation to NHTSA on November 18, 1999. Cantor recommended the use of a dummy designed with an articulated pelvis. See Regulations.gov, Docket Document No. NHTSA-1998-4064-0030 for a copy of the presentation. 3 Except for the Viano (2003) recommendation, the impactor speed for each recommendation represents the speed of the moving barrier when it strikes the stationary test vehicle. The Delta-V experienced by the test vehicle is about half of the impactor speed, depending on the mass of the vehicle. For the Viano recommendation, the 30-36 km/h impulse for the sled test corresponds to the Delta-V range observed in FMVSS No. 301 rigid barrier tests run at 54.2 km/h (33.2 mph). 4 Saczalski's 2015 petition recommended use of “NHTSA injury reference values for the head, neck, chest, and extremities” for the HIII-95 seated in the front and the CRABI seated in the rear. For convenience, we have entered IARVs for the CRABI “C” and the HIII-95M “H” in the table above that correspond to those that NHTSA recommended in Eppinger, 2000 (cited earlier)
Document Information
- Published:
- 07/16/2024
- Department:
- National Highway Traffic Safety Administration
- Entry Type:
- Proposed Rule
- Action:
- Advance notice of proposed rulemaking.
- Document Number:
- 2024-15390
- Dates:
- Comments must be received no later than September 16, 2024. The Saczalski and Cantor petitions are granted in part and the CAS petition is denied as of July 16, 2024. See ADDRESSES and Section VIII. Public Participation for more information about submitting written comments and reviewing comments submitted by other interested parties.
- Pages:
- 57998-58038 (41 pages)
- Docket Numbers:
- Docket No. NHTSA-2024-0001
- RINs:
- 2127-AM53: Seatback Safety Standards
- RIN Links:
- https://www.federalregister.gov/regulations/2127-AM53/seatback-safety-standards
- PDF File:
- 2024-15390.pdf
- CFR: (1)
- 49 CFR 571