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In rear impacts, the seat and seatbelt are intended to provide occupant restraint and maintain the occupant on the seat with favorable kinematics and low biomechanical responses. This study analyzes the lack of restraint provided by lap-shoulder belts in rear impacts with and without pretensioning and offers thoughts on ways to provide early restraint by seatbelts. Rear sled tests were conducted at 40.2 km/h (25 mph) delta V with a lap-shoulder belted, instrumented 50th Hybrid III. The dummy instrumentation included head, chest and pelvis triaxial acceleration and upper and lower neck triaxial loads and moments. Lap and shoulder belt loads were measured. High-speed video recorded different views of the occupant kinematics. In the first series, two sled tests were conducted with a Ford F-150 driver seat. One test was with the standard lap-shoulder belts only and a second with buckle pretensioner activation. In the second series, three matched tests were conducted with a Ford Escape driver seat. One test was with the lap-shoulder belts only, a second with retractor and anchor pretensioning and a third with only retractor pretensioning. The analysis included occupant kinematics, lap-belt movement and estimation of the load on the occupant's torso. The load was the sum of force on the upper and lower torso. The upper torso mass was 30.8 kg (67.8 lb) based on GEBOD data for the 50th Hybrid III. It was multiplied by the resultant chest acceleration to calculate the upper torso force. The lower-torso mass was 30.9 kg (68.0 lb). It was multiplied by the resultant pelvic acceleration to calculate the lower torso force. The total load on the seatback was the sum of the upper and lower torso force. The change in angle (θ) of the lap belt was determined by video analysis. The angle θ was from the horizontal up to a line through the lap-belt webbing. Ways to provide early lap-belt restraint were considered. The rear sled testing at 40.2 km/h (25 mph) showed that the seatbelt provided essentially no restraint of the rearward movement of the occupant. The seat provided essentially all of the rearward restraint with and without pretensioning. There was minimal lap belt load in the series with the dual recliner Escape seat, except for a spike caused by pretensioning. There was more seat deformation in the tests with the single-side recliner F-150 seat. There were higher belt loads. The lap belt limited the lifting of the hips and thighs with essentially no rearward restraint of the occupant. Tension in the lap belt did not relate to restraint of rearward movement of the occupant. Seatbelts provided forward restraint of the occupant during rebound with the belts providing noticeable deceleration of the chest and pelvis. Concepts were considered to provide early lap-belt restraint. One involved a rear pretensioner that dynamically moves the lap-belt anchor forward and upward while tightening the belts in a rear impact. This provides a lap-belt angle greater than θ = 90 deg before occupant movement. With this geometry, the lap belt restrains rearward movement of the occupant and pulls the hip down early in a rear impact. Seatbelts and pretensioners were designed for occupant restraint in frontal crashes, so it is not a surprise they do not provide much restraint of an occupant in rear impacts up to 40.2 km/h (25 mph). The lack of early lap-belt restraint is due to the unfavorable belt angle from the anchors over the hip. A concept is discussed that dynamically moves the anchors in rear impacts to provide early belt restraint. [ABSTRACT FROM AUTHOR]

Occupant kinematics and biomechanical responses are assessed with and without pretensioning of normally seated and out-of-position front-seat occupants in rear sled tests. The results are compared to recent studies. Three series of rear sled tests were conducted at 24 and 40 km/h with a 2001 Ford Taurus. Series I consisted of two sled tests with a lap-shoulder belted 50th Hybrid III in the driver seat. Series II included four sled tests with a lap-shoulder belted 50th Hybrid III in both front seats. Two soft foam blocks were added, one was placed on the chest centerline under the shoulder belt and one on the pelvis under the lap belt providing additional webbing. Series III consisted of 8 runs and 16 ATD tests to assess the effect of pretensioning with out-of-positioned (OOP) occupants. The biomechanical responses were normalized with Injury Assessment Reference Values (IARV) for head, neck and chest. The ATD kinematics and biomechanical responses were similar in the yielding phase when the occupant was normally seated with and without pretensioning. The rebound displacement was greater with pretensioning in the 40 km/h tests due to the shoulder belt slipping off the shoulder. The hip displacement was similar, irrespective of pretensioning. All biomechanical responses were below IARVs. The highest response was for lower neck extension. The normalized response was at about 32% for the 24 km/h tests, irrespective of pretensioning. It was up to 59% in the 40 km/h tests with pretensioning. With the OOP occupants, there were no differences in the kinematics and biomechanical response with pretensioning. Testing of the effect of retractor pretensioning with out-of-position occupants and additional belt webbing in moderate to high-speed rear sled tests shows no effect on occupant kinematics and biomechanical responses. The displacement of the hips in a rear impact depends on the compliance of the seatback and amount of pocketing, the stiffness of the seat frame limiting rearward rotation, and the dynamic friction between the occupant and the seatback. [ABSTRACT FROM AUTHOR]

Objective: This study compared dummy kinematics and biomechanical responses with and without retractor pretensioning in a severe rear sled test. It compliments an earlier study with buckle pretensioning.Methods: Three rear tests were run at 40 km/h (25 mph) delta V with a lap-shoulder belted Hybrid III 50th male dummy on a 2013-18 Ford Escape driver seat and belt restraint. One test was with the lap-shoulder belts only, a second with retractor and anchor pretensioning and a third with only retractor pretensioning. The head, chest and pelvis were instrumented with triaxial accelerometers. The upper and lower neck, thoracic spine and lumbar spine had transducers measuring triaxial loads and moments. Lap belt load was measured. High-speed video recorded different views of the dummy motion. Dummy kinematics and biomechanical responses were compared to determine the influence of retractor belt pretensioning.Results: The dummy kinematics and biomechanical responses were essentially similar with and without retractor or retractor and anchor pretensioning in rear sled tests. There was an initial spike in lap belt load with pretensioning, but it did not result in different dummy head, neck or chest responses. In the tests, the dummy moved rearward away from the shoulder belt. The belts were tightened with the rapid pull on the webbing by pretensioning. The dummy loaded the seat, which yielded rearward restraining its motion. There was no significant effect of pretensioning on the dynamics of the dummy until late in rebound.Conclusions: There were no significant differences in dynamics of the Hybrid III with and without retractor or retractor and anchor pretensioning in a 40 km/h (25 mph) rear sled test. Belt pretensioning did not influence biomechanical responses in the rear impact because the seat supported the dummy. [ABSTRACT FROM AUTHOR]

Objective: This study compared biomechanical responses of a normally seated Hybrid III dummy on conventional and all belts to seat (ABTS) seats in 40.2 km/h (25 mph) rear sled tests. It determined the difference in performance with modern (≥2000 MY) seats compared to older (<2000 MY) seats and ABTS seats.Methods: The seats were fixed in a sled buck subjected to a 40.2 km/h (25 mph) rear sled test. The pulse was a 15 g double-peak acceleration with 150 ms duration. The 50th percentile Hybrid III was lap-shoulder belted in the FMVSS 208 design position. The testing included 11 <2000 MY, 8 ≥2000 MY, and 7 ABTS seats. The dummy was fully instrumented, including head accelerations, upper and lower neck 6-axis load cells, chest acceleration, thoracic and lumbar spine load cells, and pelvis accelerations. The peak responses were normalized by injury assessment reference values (IARVs) to assess injury risks. Statistical analysis was conducted using Student's t test. High-speed video documented occupant kinematics.Results: Biomechanical responses were lower with modern (≥2000 MY) seats than older (<2000 MY) designs. The lower neck extension moment was 32.5 ± 9.7% of IARV in modern seats compared to 62.8 ± 31.6% in older seats (P =.01). Overall, there was a 34% reduction in the comparable biomechanical responses with modern seats. Biomechanical responses were lower with modern seats than ABTS seats. The lower neck extension moment was 41.4 ± 7.8% with all MY ABTS seats compared to 32.5 ± 9.7% in modern seats (P =.07). Overall, the ABTS seats had 13% higher biomechanical responses than the modern seats.Conclusions: Modern (≥2000 MY) design seats have lower biomechanical responses in 40.2 km/h rear sled tests than older (<2000 MY) designs and ABTS designs. The improved performance is consistent with an increase in seat strength combined with improved occupant kinematics through pocketing of the occupant into the seatback, higher and more forward head restraint, and other design changes. The methods and data presented here provide a basis for standardized testing of seats. However, a complete understanding of seat safety requires consideration of out-of-position (OOP) occupants in high-speed impacts and consideration of the much more common, low-speed rear impacts. [ABSTRACT FROM AUTHOR]

Purpose: This study collected and analyzed available testing of motor vehicle seat strength in rearward loading by a body block simulating the torso of an occupant. The data were grouped by single recliner, dual recliner, and all belts to seat (ABTS) seats.Methods: The strength of seats to rearward loading has been evaluated with body block testing from 1964 to 2008. The database of available tests includes 217 single recliner, 65 dual recliner, and 18 ABTS seats. The trends in seat strength were determined by linear regression and differences between seat types were evaluated by Student's t-test. The average peak moment and force supported by the seat was determined by decade of vehicle model year (MY).Results: Single recliner seats were used in motor vehicles in the 1960s to 1970s. The average strength was 918 ± 224 Nm (n = 26) in the 1960s and 1,069 ± 293 Nm (n = 65) in the 1980s. There has been a gradual increase in strength over time. Dual recliner seats started to phase into vehicles in the late 1980s. By the 2000s, the average strength of single recliner seats increased to 1,501 ± 335 Nm (n = 14) and dual recliner seats to 2,302 ± 699 Nm (n = 26). Dual recliner seats are significantly stronger than single recliner seats for each decade of comparison (P < .001). The average strength of ABTS seats was 4,395 ± 1,185 in-lb for 1989-2004 MY seats (n = 18). ABTS seats are significantly stronger than single or dual recliner seats (P < .001). The trend in ABTS strength is decreasing with time and converging toward that of dual recliner seats.Conclusions: Body block testing is an quantitative means of evaluating the strength of seats for occupant loading in rear impacts. There has been an increase in conventional seat strength over the past 50 years. By the 2000s, most seats are 1,700-3,400 Nm moment strength. However, the safety of a seat is more complex than its strength and depends on many other factors. [ABSTRACT FROM AUTHOR]

Objective:A number of field accident studies have found that rebound is a source for occupant injury after rear impacts. Sled tests were run to investigate occupant kinematics and rebound, including head velocity and displacement with 3 different seats, 2 conventional seat designs, and 1 all belts to seat (ABTS). Methods:Nine rear-end sled tests were run with a belted 50th Hybrid III dummy on a Taurus, Mustang, or Sebring ABTS seat in nominally 16.5, 24.1, and 32.5 km/h rear-end delta Vs. There was no sled braking after the rear acceleration to study rebound from the seat. Dummy kinematics were analyzed from high-speed video and biomechanical responses from triaxial head and chest accelerations, triaxial upper and lower neck loads and moments, and seat belt loads. Peak responses were tabulated during seat back rotation rearward and rebound forward. Ratios of biomechanical and kinematic responses were determined comparing ABTS to conventional seat responses for each delta V. Student's t-test was used to determine significant differences between the ratios of ABTS to conventional seat responses. Results:The rebound velocity of the head varied from 2.9 to 6.8 m/s with respect to the sled. Overall, it was 69 ± 22 percent higher than the sled delta V. It was greatest with ABTS in the highest severity test where seat back yielding absorbed energy and reduced rebound in the conventional seats. The time to maximum forward excursion was significantly shorter with ABTS compared to the conventional seats with a ratio of 0.54 ± 0.34 (t = 6.13, df = 5, P < .001). Conclusions:ABTS seats remain more upright in rear-end crashes and transfer greater load to the occupant during rebound than conventional seats that yield rearward and absorb energy in higher severity crashes. Rebound occurs earlier and at higher velocities with ABTS. This displaces the occupant toward the front interior. Supplemental materials are available for this article. Go to the publisher's online edition ofTraffic Injury Preventionto view the supplemental file. [ABSTRACT FROM PUBLISHER]