Analysis of the lack of restraint with and without belt pretensioning in 40.2 km/h rear impacts

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.</p

Frontal NCAP performance and field injury over 40 years

Vehicle and occupant responses in 35 mph NCAP tests were determined for small-midsize passenger cars grouped around model year (MY) 1980, 1990, 2000, 2010 and 2020. A baseline was established with 1980 vehicles not designed for NCAP. The results of four decades of vehicles designed for NCAP were compared to the baseline. The study also determined the risk for serious injury (MAIS 3 + F) by vehicle model year (MY) using 1989–2015 NASS and 2017–2020 CISS. It explored safety trends in frontal crashes over 50 MYs of vehicles. The 1980 baseline group was established with 10 1979–1983 MY passenger cars weighing The 1980 NCAP tests brought about changes in vehicle structures and occupant restraints by 1990; however, HIC15 and 3 ms chest acceleration have not changed much the past 20 years since the use of advanced airbags and seatbelts with pretensioner and load-limiters. For the driver, HIC15 dropped 40 ± 19% from the 1980 to 1990 NCAP tests and dropped further to 76 ± 32% in 2020. The percentage drops after 1990 were not statistically significant. The driver 3 ms chest acceleration dropped 18 ± 5% from 1980 to 1990 and plateaued with 22 ± 6% in 2020. For the front passenger, HIC15 dropped 68 ± 52% from the 1980 to 1990 NCAP tests and plateaued at 71 ± 49% in 2020. The passenger 3 ms chest acceleration dropped 13 ± 5% from 1980 to 1990 and has fluctuated with minimal change. Injury risks based on responses show the same initial drop in 1990 and have remained essentially constant. Nothing meaningful has changed in dummy responses in the past 20 years of NCAP testing. The field data found the belted driver MAIS 3 + F risk was 1.66 ± 0.37% in 1961–1989 MY vehicles and 1.39 ± 0.33% in 2010–2021 MY vehicles. For belted right-front passengers, the risk was 1.52 ± 0.39% in 1961–1989 MY vehicles and 1.42 ± 0.46% in 2010–2021 MY vehicles. The field data shows no meaningful change in injury risk in 50 MYs of vehicles. NCAP involves 35–40 mph delta-V, which represents a small fraction, 0.33%, of belted occupant exposure and only 8.6% of severe injury based on 1994–2015 NASS. The NCAP test lacks field relevance. Manufacturers are merely “tuning” the restraint systems for star ratings without meaningful changes in field injury risks the past 20 years. There are disbenefits of “tuning” safety for a single, high-severity crash when most of the severe injury occurs in lower severity crashes. NHTSA should reevaluate plans to change the dummy to Thor and add BrIC injury criteria to assess NCAP responses. These changes would cause manufacturers to further “tune” structures, restraints and interiors without meaningful effects in real-world crashes.</p

Mechanisms of femoral fracture

Mechanisms of femoral fracture of the condyles and shaft were experimentally investigated through controlled knee impact of denuded femurs in six human cadavers. High-speed movies recorded knee joint compression, femoral displacements and deformation, and fracture initiation. Fracture initiated at 10.6 +/- 2.7 kN knee load after 1.3 +/- 0.1 cm of knee joint compression for a 10.1 kg rigid impact at 13.2 +/- 1.4 m/s. Interestingly, fracture occurred 0.5 ms-1.5 ms after the peak in applied knee load of 18.3 +/- 6.9 kN, probably because a significant portion of the load is developed by inertial accelerations displacing the femur and coupled masses. Axial strain measurements at the femoral midshaft showed increasing anteroposterior bending and compressional deformations until the initiation of observed fracture. The kinematics of the observed fracture and the midshaft deformational strains indicate that fracture is predominantly due to tensile strain from anteroposterior bending of the femoral shaft or patellar wedging of the condyles.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/23420/1/0000368.pd

Concussion, Diffuse Axonal Injury, and AIS4+ Head Injury in Motor Vehicle Crashes

<div><p><b>Purpose</b>: This is a descriptive study of the annual incidence of brain injuries in motor vehicle crashes by type, seat belt use, and crash severity (delta <i>V</i>) using national accident data. The risk for concussion, diffuse axonal injury (DAI), and severe head injury was determined.</p><p><b>Methods</b>: 1994–2011 NASS-CDS was analyzed to estimate the number of brain injuries annually in nonejected adults involved in motor vehicle crashes. Crashes were grouped by front, side, rear, and rollover, and the effect of belt use was investigated. Light vehicles were included with model year 1994+. Head injuries were identified as concussion, DAI, severe head injury (Abbreviated Injury Scale [AIS] 4+), and skull fracture. The annual incidence, risk, and rate for different types of head injury were estimated with standard errors.</p><p><b>Results</b>: Motor vehicle crashes involved 33,191 ± 7,815 occupants with concussion, 5,665 ± 996 with AIS 4+ head injuries, 986 ± 446 with DAI, and 3,300 ± 531 with skull fracture annually. The risk was 1.64 ± 0.39% for concussion, 0.28 ± 0.05% for severe head injury (AIS 4+), 0.05 ± 0.02% for DAI, and 0.16 ± 0.03% for skull fracture in tow-away crashes. The risk for severe head injury (AIS 4+) was highest in rollovers (0.74 ± 0.16%) and lowest in rear impacts (0.17 ± 0.05%). Head injury risk depended on seat belt use, crash type, and crash severity (delta <i>V</i>). Seat belt use lowered the risk for AIS 4+ head injury by 74.8% and skull fracture by 73.2%.</p><p><b>Conclusions</b>: Concussions occur in about one out of 61 occupants in tow-away crashes. The risk was highest in rollover crashes (4.73 ± 1.09%) and it was reduced 69.2% by seat belt use. Severe brain injuries occurred less often and the risk was also reduced by seat belt use.</p></div

Size and age of fatal drivers by crash type, vehicle type and gender

Objective: The objective of this study was to determine the physical characteristics of fatal drivers in motor vehicle crashes with focus on rear impacts. Methods: 1998 to 2020 FARS data was analyzed for height, weight, and age of fatal drivers. The data was queried by gender, crash type and vehicle type. Results: The average fatal driver weighed 80.4 kg, was 173.4 cm tall, and was 43 years old. Females were 16.0 kg lighter and 14.2 cm shorter than males on average. The height was 151.2 cm for the 5th percentile female, 177.0 cm for the 50th male and 188.9 cm for the 95th male. The weight of fatal drivers increased linearly with calendar year. The increase rate was greater in females than in males. About 3% of fatal drivers were involved in rear crashes, 39.9% in frontal crashes and 36.8% in rollovers. The average fatal driver was 172.5 cm tall and weighed 81.0 kg in rear impacts. They were similar in height and weight to the overall sample. The average fatal driver in rear impacts was 46 years old, 3 years older than the overall average. Pickup truck drivers weighed 85.4 kg and were 176.8 cm tall on average. They were heavier and taller than passenger car drivers on average, which were 78.0 kg and 172.2 cm. Fatally injured minivan drivers were 10 years older than fatally injured passenger car drivers on average. The findings are compared with ATDs (anthropometric test devices) used in sled and crash testing. Conclusion: The average weight of fatal drivers increased with calendar year. The average size of fatal drivers was similar by crash types. Fatal drivers were older in rear impacts.</p

Driver injury in near- and far-side impacts: Update on the effect of front passenger belt use

<p><b>Purpose</b>: This is a study that updates earlier research on the influence of a front passenger on the risk for severe driver injury in near-side and far-side impacts. It includes the effects of belt use by the driver and passenger, identifies body regions involved in driver injury, and identifies the sources for severe driver head injury.</p> <p><b>Methods</b>: 1997–2015 NASS-CDS data were used to investigate the risk for Maximum Abbreviated Injury Scale (MAIS) 4 + F driver injury in near-side and far-side impacts by front passenger belt use and as a sole occupant in the driver seat. Side impacts were identified with GAD1 = L or R without rollover (rollover ≤ 0). Front-outboard occupants were included without ejection (ejection = 0). Injury severity was defined by MAIS and fatality (F) by TREATMNT = 1 or INJSEV = 4. Weighted data were determined. The risk for MAIS 4 + F was determined using the number of occupants with known injury status MAIS 0 + F. Standard errors were determined.</p> <p><b>Results</b>: Overall, belted drivers had greater risks for severe injury in near-side than far-side impacts. As a sole driver, the risk was 0.969 ± 0.212% for near-side and 0.313 ± 0.069% for far-side impacts (<i>P</i> < .005). The driver's risk was 0.933 ± 0.430% with an unbelted passenger and 0.596 ± 0.144% with a belted passenger in near-side impacts. The risk was 2.17 times greater with an unbelted passenger (NS). The driver's risk was 0.782 ± 0.431% with an unbelted passenger and 0.361% ± 0.114% with a belted passenger in far-side impacts. The risk was 1.57 times greater with an unbelted passenger (<i>P</i> < .10). Seat belt use was 66 to 95% effective in preventing MAIS 4 + F injury in the driver. For belted drivers, the head and thorax were the leading body regions for Abbreviated Injury Scale (AIS) 4+ injury. For near-side impacts, the leading sources for AIS 4+ head injury were the left B-pillar, roof, and other vehicle. For far-side impacts, the leading sources were the other occupant, right interior, and roof (8.5%).</p> <p><b>Conclusions</b>: Seat belt use by a passenger lowered the risk of severe driver injury in side impacts. The reduction was 54% in near-side impacts and 36% in far-side impacts. Belted drivers experienced mostly head and thoracic AIS 4+ injuries. Head injuries in the belted drivers were from contact with the side interior and the other occupant, even with a belted passenger.</p

Severe injury in multiple impacts: Analysis of 1997–2015 NASS-CDS

<p><b>Purpose</b>: This is a descriptive study of the incidence and risk for severe injury in single-impact and multi-impact crashes by belt use and crash type using NASS-CDS.</p> <p><b>Methods</b>: 1997–2015 NASS-CDS data were used to determine the distribution of crashes by the number of impacts and severe injury (Maximum Abbreviated Injury Score [MAIS] 4+F) to >15-year-old nonejected drivers by seat belt use in 1997+ MY vehicles. It compares the risk for severe injury in a single impact and in crashes involving 2, 3, or 4+ impacts in the collision with a focus on a frontal crash followed by other impacts.</p> <p><b>Results</b>: Most vehicle crashes involve a single impact (75.4% of 44,889,518 vehicles), followed by 2-impact crashes (19.6%), 3-impact crashes (5.0%) and 4+ impacts (2.6%). For lap–shoulder-belted drivers, the distribution of severe injury was 42.1% in a single impact, 29.3% in 2 impacts, 13.4% in 3 impacts, and 15.1% in 4+ impact crashes. The risk for a belted driver was 0.256 ± 0.031% in a single impact, 0.564 ± 0.079% in 2 impacts, 0.880 ± 0.125% in 3 impacts, and 2.121 ± 0.646% in 4+ impact. The increase in risk from a single crash to multi-impact collisions was statistically significant (<i>P</i> < .001).</p> <p>In a single impact, 53.8% of belted drivers were in a frontal crashes, 22.4% in side crashes, 20% in rear crashes, and 1.7% in rollover crashes. The risk for severe injury was highest in a rollover at 0.677 ± 0.250%, followed by near-side impact at 0.467 ± 0.084% and far-side impact at 0.237 ± 0.071%. Seat belt use was 82.4% effective in preventing severe injury (MAIS 4+F) in a rollover, 47.9% in a near-side impact, and 74.8% in a far-side impact.</p> <p>In 2-impact crashes with a belted driver, the most common sequence was a rear impact followed by a frontal crash at 1,843,506 (21.5%) with a risk for severe injury of 0.100 ± 0.058%. The second most common was a frontal impact followed by another frontal crash at 1,257,264 (14.7%) with a risk of 0.401 ± 0.057%. The risk was 0.658 ± 0.271% in a frontal impact followed by a rear impact. A near-side impact followed by a rear crash had the highest risk for severe injury at 2.073 ± 1.322%.</p> <p><b>Conclusions</b>: Restraint systems are generally developed for a single crash or sled test. The risk for severe injury was significantly higher in 2-, 3-, and 4+-impact crashes than a single impact. The majority (57.9%) of severe injuries occurred in multi-impact crashes with belted drivers. The evaluation of restraint performance warrants additional study in multi-impact crashes.</p