Rear Seat Occupants Research Articles

The Scope and Nature of Injuries to Rear Seat Passengers in NSW Using Linked Hospital Admission and Police Data

Objective: To compare the pattern of injuries to front and rear seat occupants and test the hypothesis that rear seat passengers of different ages sustain different patterns of injury. Method: Patients admitted to a hospital following involvement in a crash in New South Wales (NSW) Australia between 2005 and 2007 were identified using International Classification of Diseases (10th edition [ICD10]) codes. Hospital admissions data were linked with NSW police crash data using probabilistic techniques. The profiles and patterns of injury of front and rear seat passengers were compared. Logistic regression was used to examine how age influenced the pattern of injury among rear seat passengers. Results: Sixty-three percent of hospital admissions were linked with police records. One in 5 passengers were rear seat passengers. There were more unrestrained occupants in the rear (7%) compared to drivers (3%) and front seat passengers (2%). Younger (9–15 years) injured passengers were seated in the rear more often than in the front passenger position and older injured passengers (>50 years) were seated more often in the front passenger position than in the rear (15% rear compared to 5% front aged 9–15 years; 22% rear compared to 37% front aged >50 years; χ2, P < .001). There were proportionally more fatal injuries among rear seat passengers (10%) than among drivers (5%) and front seat passengers (6%), and the pattern of injury between front and rear passengers also varied. Rear seat passengers had more head and abdominal injuries and fewer thoracic and knee/lower leg injuries than front seat passengers. After adjusting for vehicle age, restraint status, travel speed, and whether or not a fatality occurred in the crash, older (>50 years) rear passengers had 6.3 times the odds of sustaining thoracic injuries (95% confidence interval [CI], 2.6–15.0) and lower odds (odds ratio [OR] = 0.4, 95% CI, 0.2–0.9) of sustaining abdominal/lumbar injuries than the youngest occupants (9–15 years).The odds of sustaining a head injury did not vary with age, and the odds of sustaining thoracic, abdominal, or lower extremity injuries did not differ significantly between rear seat passengers aged 16–50 years and 9–15 years. Conclusions: The findings suggest that there is a need for enhanced protection for rear seat passengers, because they have proportionally more fatal injuries than front-seated occupants. The frequency of abdominal injury and the differences between injury patterns observed in front seat passengers suggests a potential benefit from adding abdominal injury risk assessment to rear seat occupant protection test protocols. There is also scope to improve chest protection for older rear seat passengers.

High strength steels, stiffness of vehicle front-end structure, and risk of injury to rear seat occupants

Previous research has shown that rear seat occupant protection has decreased over model years, and front-end stiffness is a possible factor causing this trend. In this research, the effects of a change in stiffness on protection of rear seat occupants in frontal crashes were investigated. The stiffness was adjusted by using higher strength steels (DP and TRIP), or thicker metal sheets. Finite element simulations were performed, using an LS Dyna vehicle model coupled with a MADYMO dummy. Simulation results showed that an increase in stiffness, to the extent it happened in recent model years, can increase the risk of AIS3+ head injuries from 4.8% in the original model (with a stiffness of 1000N/mm) to 24.2% in a modified model (with a stiffness of 2356N/mm). The simulations also showed an increased risk of chest injury from 9.1% in the original model to 11.8% in the modified model. Distribution of injuries from real world accident data confirms the findings of the simulations.

Assessment of Vehicle and Restraint Design Changes for Mitigating Rear Seat Occupant Injuries

Objective: Investigate the combined effects of belt geometry, seat substructure, and seat belt pretensioners and load limiters on rear seat occupant injury risk.Methods: An instrumented Hybrid III 5th percentile adult female dummy was subjected to simulated frontal impacts (Δv = 45.8 km/h, peak acceleration = 27.1 g). Testing was conducted on a rear seat of a typical family sedan with modifications allowing for adjustment in upper anchorage position, mounting of an antisubmarining seat pan, and the use of seat belt pretensioners with load limiters.Results: Dummy seated posture had the strongest effect on submarining. Seat belt pretensioners with load limiters reduced head and femur excursion and decreased chest injury measurements but did not prevent submarining. The antisubmarining seat pan, on the other hand, prevented submarining in one case but could not prevent submarining with the dummy in a slouched posture. Upper anchorage position resulting in poor belt geometry was shown to increase both chest injury measures and submarining.Conclusions: The results from this study demonstrate the importance of an upright seated posture and the potential benefits of including adjustable upper anchorages to allow good sash belt fit, antisubmarining seat pans, belt buckles positioned near the seat bight, and seat belts with pretensioners and load limiters for rear seat occupants. These data can be used to inform the design of a system of restraints to reduce injuries to rear seat occupants.

Optimization of Vehicle Deceleration to Reduce Occupant Injury Risks in Frontal Impact

Objective: In vehicle frontal impacts, vehicle acceleration has a large effect on occupant loadings and injury risks. In this research, an optimal vehicle crash pulse was determined systematically to reduce injury measures of rear seat occupants by using mathematical simulations. Method: The vehicle crash pulse was optimized based on a vehicle deceleration-deformation diagram under the conditions that the initial velocity and the maximum vehicle deformation were constant. Initially, a spring–mass model was used to understand the fundamental parameters for optimization. In order to investigate the optimization under a more realistic situation, the vehicle crash pulse was also optimized using a multibody model of a Hybrid III dummy seated in the rear seat for the objective functions of chest acceleration and chest deflection. A sled test using a Hybrid III dummy was carried out to confirm the simulation results. Finally, the optimal crash pulses determined from the multibody simulation were applied to a human finite element (FE) model. Results: The optimized crash pulse to minimize the occupant deceleration had a concave shape: a high deceleration in the initial phase, low in the middle phase, and high again in the final phase. This crash pulse shape depended on the occupant restraint stiffness. The optimized crash pulse determined from the multibody simulation was comparable to that from the spring–mass model. From the sled test, it was demonstrated that the optimized crash pulse was effective for the reduction of chest acceleration. The crash pulse was also optimized for the objective function of chest deflection. The optimized crash pulse in the final phase was lower than that obtained for the minimization of chest acceleration. In the FE analysis of the human FE model, the optimized pulse for the objective function of the Hybrid III chest deflection was effective in reducing rib fracture risks. Conclusions: The optimized crash pulse has a concave shape and is dependent on the occupant restraint stiffness and maximum vehicle deformation. The shapes of the optimized crash pulse in the final phase were different for the objective functions of chest acceleration and chest deflection due to the inertial forces of the head and upper extremities. From the human FE model analysis it was found that the optimized crash pulse for the Hybrid III chest deflection can substantially reduce the risk of rib cage fractures. Supplemental materials are available for this article. Go to the publisher's online edition of Traffic Injury Prevention to view the supplemental file.

Effects of Vehicle Front-End Stiffness on Rear Seat Dummies in NCAP and FMVSS208 Tests

Objective: This study is devoted to quantifying changes in mass and stiffness of vehicles tested by the National Highway Traffic Safety Administration (NHTSA) over the past 3 decades (model years 1982 to 2010) and understanding the effect of those changes on protection of rear seat occupants. Methods: A total of 1179 tests were used, and the changes in their mass and stiffness versus their model year was quantified. Additionally, data from 439 dummies tested in rear seats of NHTSA's full frontal crashes were analyzed. Dummies were divided into 3 groups based on their reference injury criteria. Multiple regressions were performed with speed, stiffness, and mass as predicting variables for head, neck, and chest injury criteria. Results: A significant increase in mass and stiffness over model year of vehicles was observed, for passenger cars as well as large platform vehicles. The result showed a significant correlation (P-value < .05) between the increase in stiffness of the vehicles and increase in head and chest injury criteria for all dummy sizes. Conclusions: These results explain that stiffness is a significant contributor to previously reported decreases in protection of rear seat occupants over model years of vehicles. Supplemental materials are available for this article. Go to the publisher's online edition of Traffic Injury Prevention to view the supplemental file.

Child and Youth Traffic-Related Injuries: Use of a Trauma Registry to Identify Priorities for Prevention in the United Arab Emirates

Objective: Traffic-related injuries are the main cause of death during childhood and youth in the United Arab Emirates (UAE), use of safety restraints by citizens is uncommon, rollovers are frequent, and current legislation does not protect rear-seat occupants. Because little was known about the circumstances of hospitalizations for traffic injuries to guide prevention, a trauma registry was used to assess causes and determinants for traffic-related injuries during childhood and youth (<19 years) and its value for prevention. Methods: One hundred ninety-three children and youth with traffic injuries were admitted for more than 24 h at surgical wards of the main trauma hospital in the Al-Ain region during a 36-month period (2003–2006). Injuries were analyzed by age, nationality, road user and vehicle types, severity, anatomical region, and the presence of head injury using Injury Severity Scores (ISS) and the Abbreviated Injury Scale (AIS). Results: Traffic injuries represented 40 percent (n = 193) of injuries to 0- to 19-year-olds, followed by falls (39 percent). Among 15- to 19-year-olds, who accounted for 46 percent of child and youth victims, the incidence was 150/100,000 person years, compared to an incidence of 15 to 51 for younger age groups. Overall, 53 percent were vehicle occupants, 23 percent were pedestrians, 14 percent were bicyclists, 6 percent were motorcyclists, with 4 percent other. The ratio of male-to-female victims was 6.7:1; for drivers it was 33:0; and for pedestrians, bicyclists, and motorcyclists it was between 10:1 and 12:1; injured females were mainly rear-seat passengers and the male: female ratio was 1.4:1. Seventy-one percent of pedestrians were ≤9 years old. Although the ratio of UAE children to foreign children was estimated at 0.7:1 in the community, 58 percent of the injured were UAE citizens. The ratio of injured UAE: non-UAE citizens was 1.4:1 overall but 5.6:1 for drivers and 4.5:1 for motorcyclists. Forty-one percent of citizens were injured in 4-wheel drive sport utility vehicles compared to 13 percent of non-citizens. Head injuries occurred in 68 percent of vehicle occupants and 51 percent of nonoccupants, with AIS ≥ 3 injuries in 23 percent of occupants and 26 percent of nonoccupants. Sixty-seven percent of rear occupants had head injuries. Conclusions: Male drivers and vulnerable road users were at an unusually high risk relative to females. A relatively high frequency of traffic-related head injuries among UAE children and youth, including rear-seat passengers and other vehicle occupants, suggests that considerable preventable morbidity is associated with nonuse of safety restraints and/or other factors such as excess speed and rollovers of 4-wheel drive vehicles. Trauma registries can be useful for prevention; inclusion of data on safety restraints and helmet use by road user type is essential.

Influence of the pre-tightening of seat belts on the loads acting on rear seat occupants during a frontal collision

Influence of the pre-tightening of seat belts on the loads acting on rear seat occupants during a frontal collision

Optimizing the Rear Seat Environment for Older Children, Adults, and Infants

Objective: Our recent rear seat safety research found that more-forward and higher lap belt anchorage locations and much shorter and stiffer seat cushions can improve the protection of older children from 6 to 12 years old who are using the vehicle belt without a booster. The objective of this study was to investigate whether the optimal rear seat restraint systems for adults and infants are consistent with those for older children. Methods: We conducted sensitivity analyses and design optimizations for adults and for infants in a rear-facing child restraint system (CRS) using a set of MADYMO models, an automated simulation framework, and occupant belt-fit and posture prediction models from our previous studies. A series of 12 sled tests was also used to validate the computational models. Results: The optimal belt anchorage locations and the seat cushion length for older children, adults, and rear-facing CRS-seated infants conflict with each other. In particular, more-forward lap belt anchorage locations that prevent submarining for older children would reduce the protection to both adults and CRS-seated infants, although the protection is still acceptable based on regulated injury criteria. A shorter seat cushion could provide optimal protection to older children and adults but would significantly increase the CRS rotation. Conclusions: The findings of this study suggested that adaptive/adjustable restraint systems are necessary to simultaneously improve the rear seat occupant protection for all age groups. Supplemental materials are available for this article. Go to the publisher's online edition of Traffic Injury Prevention to view the supplemental file.

The analysis of safety of rear seat occupants of a passenger car during the road accident

The test results indicate that in many structural solutions of the passenger cars, dynamic loads of the rear seat passengers can be significantly higher compared to the front seat passengers, so the risk of injuries is higher for them. The work specifies examples of courses of dynamic loads that occur during the frontal collision with an obstacle and that affect the front seat and the rear seat passengers. At the same time, the attention is paid to relations between a seat occupied in a car and the probability of injuries in various road accidents.

Research on the Safety of Rear Seat Occupants in the Frontal Collision

To study the injury values rear seat occupants sustain in the frontal collision, this paper constructed the simulation model of the rear occupant restraint system of a vehicle model using MADYMO software. The influence of the rear 3-point seatbelt stiffness and retractor locking feature, the rear seat cushion stiffness and angle with the vehicle floor on head injury criterion HIC36, thorax 3ms resultant acceleration T3MS, thorax performance criterion THPC, left and right femur force of rear occupants were analysed through the simulation model. The conclusion shows that HIC36 drops when the seatbelt stiffness increases and retractor locking feature decreases compared to the original values; HIC36, T3MS, left and right femur force become less when the seat cushion stiffness decreases and angle increases compared to the original values.

Injury Risk Investigation of the Small, Rear-seat Occupant in Side Impact

For children seated next to the struck side, real-world crash outcome was determined for the rear-seat of passenger vehicles over the entire range of side impact crash severities. The method was first to calculate the actual risk for an occupant based on field data. The data sources were non-rollover, tow-away crashes from the 1997 - 2009 National Automotive Sampling System. By limiting the struck passenger vehicle to model year 1985 or newer, field data were identified for a total of 588 children. In all crashes, the child was seated in the rear-seat area on the struck side of the passenger vehicle. A matrix of MADYMO model simulations calculated the response of child dummies over the entire range of the field data. Age dependent, moderate to serious (AIS ≥ 2) injury risk curves were derived and evaluated for children in side impact. Risks to the children were calculated by combining the derived child risk curves with the MADYMO model simulations. The evaluations were conducted from the point of view of an aggregate approximation of AIS ≥ 2 injury rates across the crash severity range for the entire child group of all ages. The results were that the simulations and biomechanical injury risks reasonably matched the actual NASS-CDS-based trauma risks. For all children, the accumulated injury risk approximation was 10.66% and the field-based approximation was 10.73%. This field-based methodology focuses occupant safety design toward a more far-reaching system approach where the entire range of side-impact crash severities and occupant variability are considered. Language: en

Head Impact Contact Points for Restrained Child Occupants

Objective: Head injuries are the most common injuries sustained by children in motor vehicle crashes regardless of age, restraint, and crash direction. For rear seat occupants, the interaction of the subject with the seat back and the vehicle side interior structures has been previously highlighted. In order to advance this knowledge to the development of countermeasures, a summary of vehicle components that contributed to these injuries is needed. Therefore, the objective of this study was to create a contact map of the vehicle interior for head and face injuries to rear-seated restrained children in front crashes. Methods: The Crash Injury Research and Engineering Network (CIREN) was queried for rear-seated, restrained child occupants (age 0–15 years) in forward-facing child restraints, booster seats, or lap and shoulder belts who sustained an AIS2+ head and/or face injury in a frontal motor vehicle crash. Cases were analyzed to describe injury patterns and injury causation scenarios. A contact point map was developed to summarize the vehicle components related to injury causation of the head/face injury. Results: Twenty-one cases met the combined inclusion and exclusion criteria. Seven of the child occupants were restrained in forward-facing child restraints, 2 in belt-positioning booster seats, and 12 in lap and shoulder belts. There were 28 head and 17 facial injuries. For left rear occupants, the most common contact point was the pillar in front of the occupant's seat row; that is, B-pillar for second-row occupants, indicating a leftward kinematics. For right rear occupants, due to differences in crash dynamics, the most common contact point location was the passenger's seat back, suggesting that these occupants moved predominantly forward. Conclusions: Contact points associated with head/face injury for restrained children 0 to 15 years in frontal crashes have been delineated. In a majority of the cases, the head/face injury was the most severe injury and severe injuries to other body regions were uncommon, suggesting that efforts to mitigate head injuries for these occupants would greatly improve their overall safety. The majority of the head/face contact points were to the first row seat back and B-pillar. In these frontal crashes, the importance of head/face contact with the vehicle side structure suggests that deploying a curtain air bag in frontal impacts may help manage the energy of impact. These data advance the current understanding of injury patterns and causation in frontal crashes involving restrained rear-row occupants and can be used to develop solutions to mitigate the injuries sustained.

Patterns of correlation between vehicle occupant seat pressure and anthropometry

Seat pressure is known as a major factor of seat comfort in vehicles. In passenger vehicles, there is lacking research into the seat comfort of rear seat occupants. As accurate seat pressure measurement requires significant effort, simulation of seat pressure is evolving as a preferred method. However, analytic methods are based on complex finite element modeling and therefore are time consuming and involve high investment. Based on accurate anthropometric measurements of 64 male subjects and outboard rear seat pressure measurements in three different passenger vehicles, this study investigates if a set of parameters derived from seat pressure mapping are sensitive enough to differentiate between different seats and whether they correlate with anthropometry in linear models. In addition to the pressure map analysis, H-Points were measured with a coordinate measurement system based on palpated body landmarks and the range of H-Point locations in the three seats is provided. It was found that for the cushion, cushion contact area and cushion front area/force could be modeled by subject anthropometry, while only seatback contact area could be modeled based on anthropometry for all three vehicles. Major differences were found between the vehicles for other parameters.

Comparison of rear seat occupant injuries in AM50 and AF05 in frontal crashes

For rear seat occupants involved in motor vehicle fatal crashes, the number of fatalities of the unbelted rear seat occupants is approximately 3.8 times higher than that of the belted rear seat occupants. In part because of this finding, the National Police Agency decided that wearing a seatbelt would be mandatory for rear seat occupants in Japan from June 2008. In addition, the Japan New Car Assessment Program (J-NCAP), beginning from 2009, considered an evaluation of rear seat occupant safety. For the evaluation test, the J-NCAP has to select from either male (Hybrid III AM50) or female (Hybrid III AF05) dummies. The purpose of the present study is to evaluate different kinematic and response characteristics of Hybrid III AM50 and AF05 dummies seated in rear seats in frontal crashes. For this study, a full-frontal rigid barrier impact test and a frontal offset deformable barrier impact test were conducted following the Japanese-type approval test procedure using a small passenger car with engine displacement of 1496 cc. For occupant restraints, three-point seatbelts were worn by both Hybrid III AM50 and Hybrid III AF05 dummies in rear seats to evaluate their different kinematics. In the full-frontal rigid barrier impact test, the measured injury criteria from AF05 dummy of HIC15, neck extension moment, Nij, and 3-ms clip chest acceleration did exceed the Injury Assessment Reference Values (IARVs) for the AM50 dummy. However, in the full-frontal rigid barrier impact test, the measured injury criteria from AM50 dummy for the 3-ms clip chest acceleration did exceed IARV. Using the measured injury criteria, the injury risks of the AF05 dummy were determined to be greater than those of the AM50 dummy in the full-frontal rigid barrier impact test. Especially, the AIS3+ neck injury risks determined from the tension force, neck extension moment and Nij of the AF05 dummy were larger by 27% to 31% when compared with the risks of the AM50 dummy. The chest deflection of the AF05 dummy (45 mm) was similar to that of the AM50 dummy (43 mm); however, the AIS3+ chest injury risk from the chest deflection of the AF05 dummy (63%) was almost twice than that of the AM50 dummy (33%). From the full-frontal rigid barrier impact test results, an ‘unconstrained ilium by the lap belt’ phenomenon (that is, the lap belt slipped up and over the ilium) was seen in the AF05 dummy, as observed from the drastic drop in chest acceleration. The test results also indicated that this phenomenon also affected head acceleration and neck load. No such phenomenon was observed in the AM50 dummy test results. In the frontal offset deformable barrier impact test, the injury criteria measured from the AM50 dummy seated on the barrier-impacted side were of higher values than those measured from the AF05 dummy seated on the nonimpacted side in the rear seat. In this offset test configuration, the left-side sill acceleration (49 G) on the impacted side was higher than the right-side sill acceleration (27 G) on the nonimpacted side. This indicates that the factor of vehicle acceleration on injury criteria is similar to the factor of dummy body size on injury criteria. The results also indicated that injury criteria from the AF05 and AM50 dummies did not exceed IARVs and that the injury risks of both dummies are very similar. The measured injury criteria and injury risks in the full-frontal rigid barrier impact test results are higher than those in the frontal offset deformable barrier impact test results.

Effect of increase in weight and stiffness of vehicles on the safety of rear seat occupants

In this study, full-scale finite element (FE) simulations have been performed to identify factors affecting the protection of rear seat occupants. An FE model based on the 2001 Ford Taurus was used and coupled with a Hybrid III 5th percentile female dummy model in the rear seat of the vehicle. The dummy model was restrained using a three-point belt system. The effects of changes in the vehicle design, including changes in vehicle weight and stiffness, on injury readings of the rear seat dummy, including head injury criterion (HIC), chest acceleration and Nij, were evaluated. The simulation results were first validated against available test data for a Ford Taurus vehicle and later used for the analysis. The analysis showed that an increase in the stiffness of the vehicle can significantly increase rear seat dummy injury measures. It was shown, for example, that the HIC15 of a rear seat dummy can increase from 478 to 755 between two vehicles with an increase in stiffness from 1000 to 1557 N/mm.

Seatbelt effectiveness for rear seat occupants in full and offset frontal crash tests

In Japan, it became mandatory for rear seat occupants to wear seatbelts as of 2008. This paper summarises the results of full car crash tests for rear seat occupants, and compares the kinematics and injury risk to belted and unbelted rear sear occupants in order to show the effectiveness of seatbelts. Full-width rigid barrier and offset frontal impact tests were conducted using Hybrid III fifth percentile female and 3-year-old dummies in belted or unbelted conditions in the rear seat. In both full and offset frontal tests, the injury measures of the belted fifth female and 3-year-old dummies in the rear seat were relatively low because contact with the car interior was prevented by the seatbelt, although the head injury criterion and the chest deflection of the fifth female dummy were relatively large. In the tests with the fifth female dummy not belted, its knees and head made contact with the front seatback and the head of the front seat dummy, respectively. Due to this impact by the fifth female dummy, the injury measures of the driver dummy became high. The unbelted 3-year-old dummy moved in the passenger compartment, making contact with several locations in the car. These test results were comparable with accident analyses that show high injury risks to the chest of belted rear seat occupants, and high injury risks to the head and lower extremities in unbelted rear seat occupants.

Sensitivity of THOR and Hybrid III Dummy Lower Neck Loads to Belt Systems in Frontal Impact

Objectives: To determine head–neck biomechanics with a focus on lower neck injury metrics in frontal impact. The mid- and large-size Hybrid III dummies and the mid-size Test device for Human Occupant Restraint (THOR) were positioned on a buck. Tests were conducted at low, medium, and high (3.3, 6.7, and 15.7 m/s) change in velocities using 3 restraint types: normal 3-point belt with no pretension (type A), 10-cm pretension (type B), and 200 N pretension (type C). Repeat tests were conducted. Measured vertical and shear forces and sagittal bending moments were evaluated at the upper and lower regions of the neck to different types of belt systems and at different change in velocities. Peak values normalized with respect to the belt type A were used in the comparative analysis. Metrics transformed to the occipital condyles and T1 were also evaluated. Results: All dummies showed good repeatability. Peak measured and transformed upper and lower neck moments were greatest in the large-size dummy. The mid-size Hybrid III dummy responded with greater forces and moments than the THOR. Regardless of dummy type, anthropometry, and velocity, peak lower neck moments were more sensitive to belt types than peak lower neck forces. A similar pattern was apparent for upper neck data. Moments in the THOR were more sensitive than moments in the mid-size Hybrid III dummy. Conclusions: This study offers quantitative generic restraint-based data and addresses response differences between dummies and dummies of the same family. Because of increased sensitivity to belt types at the upper and lower necks for both forces and moments, the THOR appears to be an improvement to better assess injury potential to rear seat occupants wherein frontal impact air bags do not exist.

Impact of Belt Use by Rear-Seat Occupants on Injury Severity of Belted Drivers in New Jersey

In January 2010, legislation in New Jersey required all occupants of vehicles to wear seatbelts regardless of seating positions. Although it is known that an unbelted rear-seat passenger affects the safety of the driver, the level of the impact is not clear. The objective of this research was to identify the factors that influenced the injury severity of a belted driver with and without rear-seat occupants. Injury severity models were developed with crash data from the Fatality Analysis Reporting System for New Jersey for 2004 to 2006. The results indicated that the probability that a driver or right-front-seat occupant would sustain more-severe injuries was higher when a left-backseat, middle-backseat, or right-backseat occupant was unbelted. For vehicles with two backseat occupants (left-back and right-back), coefficient values for these variables indicated that lack of seat belt use by either occupant affected the injury severity level of a belted driver. The results showed that the right-backseat occupant had the greatest effect on the injury level of drivers compared with the left-back and middle-back occupants. Although seat belt use by a backseat occupant was found to affect the injury severity of a belted driver, this research demonstrated that the effect became more significant or increased as the number of backseat occupants in the vehicle increased.

A matched-cohort analysis of belted front and rear seat occupants in newer and older model vehicles shows that gains in front occupant safety have outpaced gains for rear seat occupants

Previous studies have suggested that rear seat occupants are at lower risk of serious injury and death in crashes. However, over the last 10–15 years there have been significant changes in front seat safety systems. The aim of this study was to determine whether there is still a benefit for rear seated occupants compared to front seat occupants. A matched-cohort approach, using data on restrained occupants from the US National Automotive Sampling System (data years 1993–2007), was adopted. Conditional poisson regression modeling was used to evaluate the relative risk of AIS3+ injury in front (passenger and driver) and rear seat occupants, in vehicles of model year 1990–1996 compared to newer vehicles. Occupant age, belt type, and intrusion were additional variables in the model. The relative risk of AIS3+ injury for front and rear occupants was influenced by age and model year. For those aged 16–50 years in older vehicles, the front and rear seat offered similar levels of protection (RR = 1.14, CI = 1.09–1.19), however in newer model vehicles (1997–2007), the rear seat carried a higher risk of injury (RR = 1.98, CI = 1.90–2.06). For adults over 50 years, the rear seat carried a higher risk in both older and newer vehicles, and for 9–15 year olds, the rear seat carried a lower risk. These findings suggest that safety for front seat occupants has improved over the last decade, to the point where, for occupants over 15 years of age, the front seat is safer than the rear seat. While the benefit of rear seating for children aged 9–15 years has decreased over time, they are still at lower risk in the rear seat.

Rear-Seat Motor Vehicle Travel in the U.S.: Using National Data to Define a Population at Risk

Recent studies suggest that the relative protection offered by rear seating in motor vehicle crashes has decreased, potentially reflecting disproportionate advancements in front-seat safety technology. Safe adaptation of advanced front-seat restraint systems for the rear-seat environment will require exposure data that are currently unavailable. This study uses national data to quantify rear-seat occupancy patterns, restraint use, and annual travel exposure in the U.S. in order to support the development of advanced crash protection systems for rear-seat motor vehicle occupants. Data from the 2000-2006 National Automotive Sampling System Crashworthiness Data System and 2001 National Household Transportation Survey were analyzed in 2008 to quantify occupancy patterns (e.g., seat position, restraint use) and annual person-trips for rear-seat passengers in the U.S. The overall proportion of person-trips by rear-seat occupants is relatively low (12.9%); however national at-risk exposure remains significant (approximately 39 billion annual person-trips). Annual rear-seat travel exposure is similar among children < or = 12 years and adults (18.9 vs 19.1 billion person-trips) despite the fact that children are proportionally much more likely to ride in rear positions (79.3% vs 7.4%). Restraint use among adult rear-seat occupants was also much lower than among front-seat occupants (50.4% vs 82.2%). While rear-seat occupancy is relatively low compared with front-seat occupancy at-risk rear-seat travel by both child and adult passengers in the U.S. remains significant. Restraint use by rear-seat occupants is much lower than that among front-seat passengers, particularly among adults and older children, substantially increasing injury risk. Development of future crash protection systems for rear-seat passengers must account for these exposure patterns to ensure safe and effective integration into production vehicles.