Lap Belt Fit Research Articles

The influence of seated postures and anthropometry on lap belt fit in vehicle occupants: A 3D computed tomography study

Objective In vehicle frontal collisions, it is crucial that the lap belt is designed to engage with the anterior superior iliac spine (ASIS) of occupants for a reliable restraint. This study aims to understand the influence of different seated postures on the geometrical relationship of the seat belt and the pelvis for various occupants using 3D upright and supine computed tomography (CT) systems. Methods The 3D shapes of bones and soft tissues around the pelvis were acquired through a CT scan for 30 participants. They were seated in a rigid seat equipped with a lap belt simulating the front seat of a small car, and wore a lap belt in three seated postures: upright, slouched and reclined. Parameters related to the likelihood of submarining occurrences, such as belt-ASIS overlap (an index for assessing the potential engagement of the lap belt with the ASIS) and the belt-pelvis angle (the difference between the belt angle and the normal direction of the anterior edge of the ilium) were compared. Results It was observed that the pelvis angle tilted rearward as the hip point was positioned forward and seatback angle increased. This can be seen in the slouched and reclined posture. The belt-pelvis angle was comparable between the slouched and the reclined postures, and was closer to zero (indicating that the lap belt path is closer to perpendicular to the anterior edge of the ilium) compared to the upright posture. In contrast, the belt-ASIS overlap increased with an increasing flesh margin of the ASIS and shallower belt angle. This suggests that the belt-pelvis angle is influenced by the seated posture whereas the belt-ASIS overlap is dependent more on an individual’s anthropometry. The plot of belt-pelvis angle and belt-ASIS overlap exhibited significant variability among participants. Conclusions The belt-pelvis angle and the belt-ASIS overlap of individuals will provide valuable information for understanding the current belt-fit location and predicting submarining occurrences for individuals in various postures when designing restraint systems.

Comparison of child and ATD belt fit and posture on belt-positioning boosters during self-selected, holding device, and nominal conditions

ObjectivePediatric anthropomorphic test devices (ATDs) are important tools for the assessment of child occupant protection and should represent realistic child belt fit and posture on belt-positioning boosters. Previous comparisons have been made to children in either self-selected or nominal postural conditions. This study compares belt fit and postural measurements between pediatric ATDs and a single cohort of children assuming different postures on boosters: self-selected, holding a portable electronic device, and nominal. MethodsA cohort of children (n = 25) were evaluated in a stationary vehicle on five boosters and in three postural conditions: nominal, self-selected, and a representative holding electronic device position. The Hybrid III 6- and 10-year-old and Q-Series 6- and 10-year-old ATDs were evaluated in the same five boosters and in two postural conditions: nominal and a representative holding electronic device position. A 3D coordinate measurement device was used to quantify belt fit (shoulder belt score, lap belt score, maximum gap size, and gap length) and anatomic landmark positions (head, suprasternale, ASIS, and patella). Landmark positions and belt fit were compared between ATDs and children for each booster and postural condition, and Pearson correlations (r) were assessed across boosters. ResultsATDs generally represented Nominal child postures across boosters. In the Device condition, ATDs were seldom able to be positioned to represent both the torso and head position of children, due to limited ATD spinal flexibility. When the torso position was matched, the ATD head was more rear by 63 mm. Correlations between Nominal child and ATD belt fit and belt gap metrics were generally weak and not significant, with the exception of lap belt score (all ATDs p < 0.07, r = 0.8549–0.9857). DiscussionATDs were generally able to represent realistic child postures and lap belt fit in Nominal and short duration Self-selected postures in a laboratory setting. However, these results display the potential difficulty of utilizing ATDs to represent more naturalistic child postures, especially the more forward head positions and flexed spinal posture associated with utilizing a portable electronic device.

Belt fit for children in vehicle seats with and without belt-positioning boosters

Objective The purpose of the current study is to use 3D technology to measure in-vehicle belt fit both with and without booster seats across different vehicles among a large, diverse sample of children and to compare belt fit with and without a booster. Methods Lap and shoulder belt fit were measured for 108 children ages 6–12 years sitting in the second-row, outboard seats of three vehicles from October 2017 to March 2018. Each child was measured with no booster, a backless booster, and a high-back (HB) booster in three different vehicles. Alternative high-back (HB HW) and backless boosters that could accommodate higher weights were used for children who were too large to fit in the standard boosters. Lap and torso belt scores were computed based on the belt location relative to skeletal landmarks. Results Both lap and torso belt fit scores were significantly different across vehicles when using the vehicle belt alone (no booster). In all vehicles, lap belt fit improved when using boosters compared with no booster among children ages 6–12 years in rear seats—with one exception of the HB HW booster in the minivan. Torso belt fit improved when using boosters compared with no booster in the sedan, and torso belt fit improved in the minivan and SUV with the use of HB and HB HW boosters when compared with no booster. Conclusions Lap and torso belt fit for children ages 6–12 years in rear seats was substantially improved by using boosters. Parents and caregivers should continue to have their children use booster seats until vehicle seat belts fit properly which likely does not occur until children are 9–12 years old. Decision makers can consider strengthening child passenger restraint laws with booster seat provisions that require children who have outgrown car seats to use booster seats until at least age 9 to improve belt fit and reduce crash injuries and deaths.

Comparison of three-point belt fit between humans and Hybrid-III anthropometric test devices in a driver mockup

Objective: The Hybrid-III anthropometric test devices (ATDs) are widely used by the automotive industry to evaluate restraint system performance in standardized vehicle crash tests. The relationship between the belt fit measured for people in driving posture and the belt fit obtained with ATDs has not been reported in the literature. The present study compares lap and shoulder belt fit data from ATDs and to a statistical estimate for drivers using age, stature, and BMI.Methods: The lap and shoulder belt fits were measured for small-female and midsize-male Hybrid-III ATDs in a laboratory mockup of a midsize sedan. A range of lower and upper belt anchorage locations were used. The ATD belt fit data were compared with predictions from a regression model developed by data from 97 men and women measured in the same driving package conditions. Humans were free to position the belt comfortably, even if the position was not optimal.Results: The measurements of the ATD belt fit were obtained and compared to the regression estimate for a driver using age, stature, and BMI as predictors. For the small female, the ATD’s lap belt was placed 46 mm further forward and 12 mm lower relative to the pelvis than the regression model estimates for a driver’s lap belt placement. For the midsize male, the lap portion of the belt was placed 13 mm more rearward and 33 mm lower on the physical ATD than the regression model estimates for a similarly sized driver. The shoulder belt was placed an average of 66 mm more inboard and 11 mm more outboard on the small-female and midsize-male physical ATDs, respectively, compared with regression model estimates for drivers.Conclusions: Differences in the lap and shoulder belt fits were quantified between the physical ATDs and regression predictions for similarly sized humans in driving postures. The consequences of these differences should be investigated to help increase understanding of the relationship between belt fit and belt performance.

Comparison of three-point belt fit between humans and ATDs in rear seats

ABSTRACTObjective: The anthropomorphic test devices (ATDs) in the Hybrid III family are widely used as human surrogates to test the crash performance of vehicles. A previous study demonstrated that passenger belt fit in rear seats was affected by high body mass index (BMI) and to a lesser extent by increased age. Specifically, the lap belt was worn higher and more forward as BMI and age increased. The objective of this study was to compare passenger belt fit to the belt fit achieved when installing the small female and midsize male Hybrid III adult ATDs using standard procedures.Methods: The ATDs were installed using standardized procedures in the same conditions previously used with volunteers. Belt fit was measured using methods analogous to those used for the volunteers. Comparative human belt fit values were obtained by using regression analysis with the volunteer data to calculate the mean expected belt fit for people the same size as the ATDs.Results: For the small female ATD, the upper edge of the lap belt was on average 59 mm forward and 11 mm above the anterior–superior iliac spine (ASIS) landmark on the ATD pelvis bone. In contrast, the belt position for similar size passengers was 17 mm forward and 22 mm above the ASIS. For the midsize male ATD, the belt was 34 mm forward and 10 mm above the ASIS. For similar size passengers, the position was 38 mm forward and 44 mm above the ASIS. For context, the belt width in this study was 38 mm.Discussion: The results suggest that the lap belt fit obtained by ATDs is more idealized but more repeatable compared to that achieved by similar size passengers. Future standardization efforts should consider investigating whether new belt-positioning procedures with ATDs may improve the biofidelity of ATD response.

Evaluating an intervention to improve belt fit for adult occupants

IntroductionPrevious laboratory studies have demonstrated that some drivers position their seat belts suboptimally. Specifically, the lap portion of the belt may be higher and farther forward relative to the pelvis than best practice, and the shoulder portion of the belt may be outboard or inboard of mid-shoulder. This study evaluated the performance of a video-based intervention for improving the belt fit obtained by drivers. MethodTwenty-nine adult drivers participated in this study. Belt fit was measured before and after the intervention in participants’ vehicles and in a laboratory mockup. ResultsData from both the in-vehicle and laboratory belt measures found that 95% of participants sampled improved some aspect of lap belt fit. For the in-vehicle test conditions, participants who lowered the lap belt location (Z) after the intervention showed an improvement of 26 mm on average. Among those participants who shifted the horizontal lap belt location rearward (closer to the pelvis), an average improvement of 36 mm was observed. No significant differences were observed between baseline and post-intervention shoulder belt fit. ConclusionsThe results provide preliminary evidence that an intervention improves driver belt fit. More research is needed to establish what aspects of this intervention affected behavior and how effective such an intervention is in the context of public health. Practical applicationsThese findings can help better inform intervention initiatives to improve occupant belt fit.

Predicting vehicle belt fit for children ages 6–12

ABSTRACTObjective: To predict shoulder belt fit and lap belt fit as a function of child age, vehicle seat characteristics, and belt geometry.Methods: In a previous study, the lap belt and shoulder belt fit of 44 children aged 5–12 were measured in a simulated vehicle seat while varying cushion length, cushion angle, seatback angle, and belt anchorage geometry. A regression model was developed to predict lap belt fit and shoulder belt fit as a function of vehicle parameters and child stature. These regression models were applied to the stature distribution of 6- to 12-year-olds using a range of vehicle geometry data to predict the proportion of children expected to achieve good belt fit in the second-row, outboard seating positions of 46 vehicles when not using belt-positioning boosters.Results: Across the ranges observed in vehicles, lap belt angle had the strongest effect on lap belt fit, although vehicle cushion length also contributed. Shoulder belt fit was most strongly affected by D-ring location. Vehicles with the geometric conditions most suitable for children are estimated to provide good lap belt fit for 25% of children aged 6 to 12. In 20% of vehicles, the shoulder belt is too far inboard for the target child population; 20% of vehicles are estimated to have shoulder belt fit too far outboard for children ages 6 to 12.Conclusions: Based on this geometric analysis, the rear seats of most vehicles are unlikely to provide good lap belt fit for up to 75% of children ages 6–12. Shoulder belt fit is outside the target range for 40% of children. Consequently, children under 12 years of age are likely to experience markedly poorer belt fit when transitioning out of a booster seat.

Seat belt use and fit among drivers aged 75 years and older in their own vehicles

ABSTRACTObjective: This article aims to describe seat belt wearing patterns and quality of seat belt fit among drivers aged 75 years and older. A secondary aim is to explore associations between body shape, comfort, and seat belt use patterns.Methods: This is an observation and survey study of a cohort of 380 drivers aged 75 years and over. During home visits, photographs were taken of the drivers in their vehicles for later analysis of belt fit and a short survey was also administered to collect demographic data and information about seat belt use and comfort. Seat belt fit and use of belt and seat accessories were analyzed from the photographs.Results: Data from 367 participants with photographs were analyzed. Whereas 97% reported using a seat belt and 90% reported their seat belt to be comfortable, 21% reported repositioning their seat belt to improve comfort. Good sash and lap belt fit were achieved in 53 and 59% of participants, respectively, but only 35% achieved overall good fit. Both poor sash and lap belt fit were observed in 23% of participants. Drivers who were in the obese category had over twice the odds (95% confidence interval [CI], 1.2–4.1) of having a poor lap belt fit than those in the normal body mass index [BMI] range, and drivers who were overweight had 1.8 times the odds (95% CI, 1.1–2.9) of having poor lap belt fit. Older females also had twice the odds (95% CI, 1.3–3.5) of poor lap belt fit compared to older males, regardless of BMI. Sash belt fit did not vary significantly by BMI, stature, or gender. However older drivers who reported that they had not made any adjustments to the D-ring height had 1.7 times the odds of having poor sash belt fit than those who made adjustments (1.2–2.9). Females were 7.3 times more likely to report comfort problems than males (95% CI, 3.2, 16.3) but there was no association between reported comfort and BMI or seat belt fit. Drivers who reported comfort problems had 6 times the odds (3.2–13.6) of also reporting active repositioning of the belt.Conclusions: The results suggest that older drivers face challenges in achieving comfortable and correct seat belt fit. This may have a negative impact on crash protection. Belt fit problems appear to be associated with body shape, particularly high BMI and gender. There is a need for further investigation of comfort accessories; in the interim, older drivers and occupants should be encouraged to use features such as D-ring adjusters to improve sash belt fit.

Nature and etiology of hollow-organ abdominal injuries in frontal crashes

Injuries to the hollow organs of the lower digestive system carry substantial risk of complication due to infection and blood loss, and commonly require invasive abdominal surgery to diagnose and treat. The causes of, and risk factors for, lower abdomen injury in automobile collisions are poorly understood. The goal of this study was to investigate the risk factors and potential mechanisms of hollow-organ, lower abdomen injury in belted automobile occupants in frontal collisions.A field survey data analysis was performed to examine the relationship between various occupant and collision factors and the risk of moderate or greater severity injury (i.e., Abbreviated Injury Scale, AIS 2+) to the small intestine, large intestine, or mesentery among belted occupants involved in frontal collisions. Descriptive and comparative risk factor analyses were performed with data originating from that National Automotive Sampling System Crashworthiness Data System (NASS-CDS) over the years 2000–2011. Multivariable logistic regression models were developed to describe the effects of these factors on hollow-organ injury risk. Potential injury mechanisms were further investigated through in-depth examination of select cases exhibiting hollow-organ injuries from the Crash Investigation Research and Engineering Network (CIREN).The inclusion criteria yielded 25,407 individual cases from NASS-CDS, representing a weighted population of 11,373,358 exposed automobile occupants. Within this dataset, 143 cases (weighted frequency: 7962 occupants) exhibited AIS 2+ injury to hollow abdominal organs. Multivariable regression analysis indicated a statistically significant increased risk of moderate or greater severity injuries to the hollow organs of the abdomen with increased in ΔV (odds ratio (OR) 1.07, 95% confidence interval: 1.06–1.09) and age (OR: 1.03, 1.01–1.06). Albeit non-statistically significant, a positive association between BMI and injury risk was observed, especially among obese individuals (OR: 3.55, 0.82–15.2). No association was observed for gender or seated location within the vehicle. Resultfrom this study indicate that hollow abdominal organ injury is a universal problem in frontal collisions, not confined to a specific gender or seating location. Examination of CIREN cases suggests these types of injuries are associated with direct loading of the lower abdomen by the lap belt, either through poor initial belt positioning or through a “submarining” type of kinematic where the lap belt slips off of the pelvis and loads into the abdomen. Potential countermeasures against hollow-organ abdominal injury should include measures to improve initial lap belt fit, and to retain engagement of the lap belt on the pelvis throughout the collision event.

Effects of Obesity on Seat Belt Fit

Introduction: Obesity has been shown to increase the risks of some types of injury in crashes. One way in which obesity may increase injury risk is by changing the routing of the belt relative to the underlying skeletal structures. Methods: Belt fit was measured in a laboratory study of 54 men and women, 48 percent of whom were obese, defined by body mass index (BMI) of 30 kg/m2 or greater. Test conditions included a wide range of upper and lower belt anchorage locations and ranges of seat height, seat cushion angle, and seat back angle spanning the conditions in a large fraction of front and rear seats in passenger cars and light trucks. In some conditions, foot position was restricted to simulate the typical situation in the second row of a small sedan. Results: Across individuals, an increase in BMI of 10 kg/m2 was associated with a lap belt positioned 43 mm further forward and 21 mm higher relative to the anterior–superior iliac spines of the pelvis. Each 10 kg/m2 increase in BMI was associated with an increase in lap belt webbing length of 130 mm. The worsening of lap belt fit with restricted foot position was slightly greater for obese participants. Obesity was associated with a more-inboard shoulder belt routing across a wide range of upper belt anchorage locations, and the shoulder belt webbing length between the D-ring and latch plate increased by an average of 60 mm with each 10 kg/m2 increase in BMI. Discussion and Conclusions: The results suggest that obesity effectively introduces slack in the seat belt system by routing the belt further away from the skeleton. Particularly in frontal crashes, but also in rollovers and other scenarios, this slack will result in increased excursions and an increased likelihood and severity of contacts with the interior. The higher routing of the lap belt with respect to the pelvis also increases the likelihood of submarining in frontal crashes.

Effects of vehicle seat and belt geometry on belt fit for children with and without belt positioning booster seats

A laboratory study was conducted to quantify the effects of belt-positioning boosters on lap and shoulder belt fit. Postures and belt fit were measured for forty-four boys and girls ages 5–12 in four highback boosters, one backless booster, and on a vehicle seat without a booster. Belt anchorage locations were varied over a wide range. Seat cushion angle, seat back angle, and seat cushion length were varied in the no-booster conditions.All boosters produced better mean lap belt fit than was observed in the no-booster condition, but the differences among boosters were relatively large. With one midrange belt configuration, the lap belt was not fully below the anterior–superior iliac spine (ASIS) landmark on the front of the pelvis for 89% of children in one booster, and 75% of children failed to achieve that level of belt fit in another. In contrast, the lap belt was fully below the ASIS for all but two children in the best-performing booster. Child body size had a statistically significant but relatively small effect on lap belt fit. The largest children sitting without a booster had approximately the same lap belt fit as the smallest children experienced in the worst-performing booster. Increasing lap belt angle relative to horizontal produced significantly better lap belt fit in the no-booster condition, but the boosters isolated the children from the effects of lap belt angles. Reducing seat cushion length in the no-booster condition improved lap belt fit but changing cushion angle did not.Belt upper anchorage (D-ring) location had a strong effect on shoulder belt fit in conditions without shoulder belt routing from the booster. Unexpectedly, the worst average shoulder belt fit was observed in one highback booster with a poorly positioned shoulder belt routing clip. The shoulder belt was routed more outboard, on average, with a backless booster than without a booster, but raising the child also amplified the effect of D-ring location, such that children were more likely to experience poor shoulder belt fit due to outboard and forward D-ring locations when sitting on the booster. Taller children experienced more-outboard shoulder belt fit in conditions without shoulder belt routing by the booster and in the one booster with poor shoulder belt routing. Adjustable shoulder belt routing on three of the highback boosters effectively eliminated stature effects, providing approximately the same shoulder belt fit for all children. Seat back angle did not have a significant effect on shoulder belt fit.The results of this study have broad applicability toward the improvement of occupant restraints for children The data show substantial effects of booster design on belt fit, particularly the effects of alternative lap and torso belt routing approaches. The data quantify the critical importance of belt anchorage location for child belt fit, providing an important foundation for efforts to optimize belt geometry for children.

Evaluation of the static belt fit provided by belt-positioning booster seats

Belt-positioning booster seats are recommended for children who use vehicle seat belts as primary restraints but who are too small to obtain good belt fit. Previous research has shown that belt-positioning boosters reduce injury risk, but the belt fit produced by the wide range of boosters in the US market has not previously been assessed. The present study describes the development of a method for quantifying static belt fit with a Hybrid-III 6-year-old test dummy. The measurement method was applied in a laboratory seat mockup to 31 boosters (10 in both backless and highback modes) across a range of belt geometries obtained from in-vehicle measurements. Belt fit varied widely across boosters. Backless boosters generally produced better lap belt fit than highback boosters, largely because adding the back component moved the dummy forward with respect to the lap belt routing guides. However, highback boosters produced more consistent shoulder belt fit because of the presence of belt routing guides near the shoulder. Some boosters performed well on both lap belt and shoulder belt fit. Lap belt fit in dedicated boosters was generally better than in combination restraints that also can be used with an integrated harness. Results demonstrate that certain booster design features produce better belt fit across a wide range of belt geometries. Lap belt guides that hold the belt down, rather than up, and shoulder belt guides integrated into the booster backrest provided better belt fit.

The Need for Enhanced Protocols for Assessing the Dynamic Performance of Booster Seats in Frontal Impacts

Objective: The primary objective of this work was to examine variations in the level of crash protection provided by different models of high-back booster seats in frontal impact. Secondary objectives included examination of the influence that specific belt positioning features have on the ability of a booster to achieve and maintain good seat belt fit; and the relationship between dummy loads, motion, and belt fit, both statically (pre-impact) and dynamically (during impact). Methods: Seventeen different models of high-back booster seats were subjected to simulated frontal impacts on a rebound crash sled. The TNO P10 dummy, instrumented to measure head and chest accelerations and targeted to allow head motion tracking, was used in these tests. Three high-speed cameras were used to record dummy motion. Associations between pre-impact seat belt geometry, the dynamic seat belt fit, and dummy response were examined. Results: Clear variations were observed in the level of protection provided by the booster seats tested. Specifically, there were variations in the ability to provide and maintain good seat belt fit. Only three of the seventeen booster seats provided good sash (shoulder) and lap belt fit during dynamic testing. All seventeen boosters had a “sash guide.” Sash guide type did not appear to influence the dynamic belt fit. However, the location of the guide and ultimately where on the shoulder the sash was positioned pre-impact did influence the dynamic sash fit. Anti-submarine clips (ASCs) that work to position the lap belt low on the abdomen were also found to maintain good lap belt fit during the dynamic tests. However, two booster seats without ASCs were also able to maintain good dynamic lap belt fit, although the mechanism of this behavior is less clear. Though there was a relationship between head excursion, head acceleration and the pre-impact static position of the sash belt (shoulder belt), there was no relationship between dummy response and the overall ability of a booster seat to provide and maintain both good sash and lap belt fit. Conclusions: Booster seats aim to achieve a good seat belt fit for children too small to use the adult seat belt. Variations in dynamic seat belt fit observed among these seventeen commercially available booster seats demonstrate the need for regulatory protocols that incorporate assessment of dynamic seat belt fit. With current technologies, visual examination of the seat belt during dynamic testing is the best method for assessing this performance.

Do parents choose appropriate automotive restraint devices for their children?

This study aims to describe parental choices of childhood automotive restraints and compare them with guidelines based on weight and height. Parents were surveyed and their children's heights and weight were measured. Results indicated that many parents believed their child fit a lap or shoulder belt when their children were too short to fit these devices. For children weighing < 40 pounds, 45% of parents believed the lap belt fit. Thirteen percent of 4-7-year-olds used booster seats, appropriate for 72% by sitting height criteria; and 33% of children < or = 7 years used the lap/shoullder belt, appropriate for 8% by sitting height criteria. Implications are that parental perceptions of fit may lead to inappropriate restraint choices for children. Practitioners should discuss child restraint use with parents in the context of their child's weight and height.

Assessment of the static fit of automobile lap-belt systems on front-seat passengers.

While automobile seat belts are recognized as reducing injury in frontal collisions, the lap belt can cause injury to the abdominal contents during impact. A lap belt which is malpositioned, i.e., above the anterior superior iliac spines (ASIS) of the pelvis before impact, is suggested as a causative factor in many of these injuries. A questionnaire was completed by 198 adult passengers on lap-belt fit as well as vehicle, anthropometric and behavioural factors. All measures were self-reported. The fit of automobile seat belts was also investigated in the laboratory to determine some of the factors thought important in the pre-impact position of the lap belt. Seven factors, subject size, subject sitting posture, clothing thickness, vehicle configuration, vehicle seat position, seat back angle and the handling of the belt by the occupant, were assessed on 51 subjects sitting in six simulated vehicles. The sample purposely included a disproportionate number of tall, short, heavy and thin subjects. The questi...