A Visual-Vestibular Model to Predict Motion Sickness for Linear and Angular Motion.

OBJECTIVE: This study proposed a model to predict passenger motion sickness under the presence of a visual-vestibular conflict and assessed its performance with respect to previously recorded experimental data. BACKGROUND: While several models have been shown useful to predict motion sickness under repetitive motion, improvements are still desired in terms of predicting motion sickness in realistic driving conditions. There remains a need for a model that considers angular and linear visual-vestibular motion inputs in three dimensions to improve prediction of passenger motion sickness. METHOD: The model combined the subjective vertical conflict theory and human motion perception models. The proposed model integrates visual and vestibular sensed 6 DoF motion signals in a novel architecture. RESULTS: Model prediction results were compared to motion sickness data obtained from studies conducted in motion simulators as well as on-road vehicle testing, yielding trends that are congruent with observed results in both cases. CONCLUSION: The model demonstrated the ability to predict trends in motion sickness response for conditions in which a passenger performs a task on a handheld device versus facing forward looking ahead under realistic driving conditions. However, further analysis across a larger population is necessary to better assess the model's performance. APPLICATION: The proposed model can be used as a tool to predict motion sickness under different levels of visual-vestibular conflict. This can be leveraged to design interventions capable of mitigating passenger motion sickness. Further, this model can provide insights that aid in the development of passenger experiences inside autonomous vehicles.

A parametric modeling of adult body shape in a supported seated posture including effects of age.

Statistical body shape models (SBSM) provide compact, flexible representations of body shape that can be implemented in design software. However, few SBSMs have been created to represent adults in supported seated postures that are relevant for the design of seated environments, and none has incorporated the effects of age. This paper presents an SBSM based on surface laser-scan data from 155 U.S. adults. The data were processed to obtain homologous mesh structure and symmetric geometry, and the processed data were statistically analysed using principal component analysis to obtain a compact representation of the data variance. Regression analysis was conducted to predict body size and shape from stature, body mass index, ratio of sitting height to stature, sex, and age. The resulting model allows rapid generation of realistic body models for applications, including product design, accommodation assessment, and safety system optimisation. The model is publicly accessible at HumanShape.org. Practitioner summary: This paper presents a statistical model that represents adult body shapes in a supported seated posture based on 3 D anthropometric measurements. This model is the first whole-body parametric model known to incorporate age effects based on data extending beyond 65 years of age.

Post-Drive Standing Balance of Vehicle Passengers Using Wearable Sensors: The Effect of On-Road Driving and Task Performance.

Postural sway has been demonstrated to increase following exposure to different types of motion. However, limited prior studies have investigated the relationship between exposure to normative on-road driving conditions and standing balance following the exposure. The purpose of this on-road study was to quantify the effect of vehicle motion and task performance on passengers' post-drive standing balance performance. In this study, trunk-based kinematic data were captured while participants performed a series of balance exercises before and after an on-road driving session in real-time traffic. Postural sway for all balance exercises increased following the driving session. Performing a series of ecologically relevant visual-based tasks led to increases in most post-drive balance metrics such as sway position and velocity. However, the post-drive changes following the driving session with a task were not significantly different compared to changes observed following the driving session without a task. The post-drive standing balance performance changes observed in this study may increase vulnerable users' risk of falling. Wearable sensors offer an opportunity to monitor postural sway following in-vehicle exposures.

Static, Dynamic, and Cognitive Fit of Exosystems for the Human Operator.

OBJECTIVE: To define static, dynamic, and cognitive fit and their interactions as they pertain to exosystems and to document open research needs in using these fit characteristics to inform exosystem design. BACKGROUND: Initial exosystem sizing and fit evaluations are currently based on scalar anthropometric dimensions and subjective assessments. As fit depends on ongoing interactions related to task setting and user, attempts to tailor equipment have limitations when optimizing for this limited fit definition. METHOD: A targeted literature review was conducted to inform a conceptual framework defining three characteristics of exosystem fit: static, dynamic, and cognitive. Details are provided on the importance of differentiating fit characteristics for developing exosystems. RESULTS: Static fit considers alignment between human and equipment and requires understanding anthropometric characteristics of target users and geometric equipment features. Dynamic fit assesses how the human and equipment move and interact with each other, with a focus on the relative alignment between the two systems. Cognitive fit considers the stages of human-information processing, including somatosensation, executive function, and motor selection. Human cognitive capabilities should remain available to process task- and stimulus-related information in the presence of an exosystem. Dynamic and cognitive fit are operationalized in a task-specific manner, while static fit can be considered for predefined postures. CONCLUSION: A deeper understanding of how an exosystem fits an individual is needed to ensure good human-system performance. Development of methods for evaluating different fit characteristics is necessary. APPLICATION: Methods are presented to inform exosystem evaluation across physical and cognitive characteristics.

Anthropometric Dimensions of Individuals With High Body Mass Index.

OBJECTIVE: This study presents anthropometric data for individuals with high body mass index (BMI). Modified anthropometric dimensions were also developed to address the challenges of obtaining accurate and repeatable data for this population segment. BACKGROUND: The prevalence of obesity affects approximately 40% of the U.S. adult population. Anthropometric data are needed to guide product design and safety, but few individuals with high BMI have been measured in available datasets. METHOD: Anthropometric data for a convenience sample of 288 adults with high BMI (≥30 kg/m2) were collected. To increase participation and minimize participant discomfort, measurements were collected at three bariatric weight loss clinics and one academic research institution. RESULTS: The current obese cohort are heavier than the U.S. general population, with a difference in mean body weight of 47 kg for women and 56 kg for men. The obese cohort are also heavier and have a higher BMI compared with the NIOSH (National Institute for Occupational Safety and Health) truck driver population. Waist circumferential measures of the current obese cohort were larger than women or men in either population compared, a result indicative of meaningful body shape differences. CONCLUSION: To our knowledge, this study is the first to collect anthropometric data for the obese population segment and conduct comparisons to the U.S. general population and available occupational databases. The obese cohort differed substantially with respect to the distributions of anthropometric variables. APPLICATION: These data provide insights about the obese population segment that are relevant to product design, and establish a foundation for future data collection efforts.

Motion sickness in passenger vehicles during test track operations.

As automation transforms drivers into passengers, the deployment of automated vehicles (AVs) has the potential to greatly increase the incidence of motion sickness. A study was conducted to quantify motion sickness response of front-seat passengers performing ecologically relevant passenger activities during conditions consistent with driving on public roadways. Fifty-two adults with a large range of self-reported levels of motion sickness susceptibility and age participated in data collection on a closed test track in a passenger sedan. Motion sickness ratings increased with task vs. no-task and moderate vs. low acceleration test conditions. Increased motion sickness susceptibility was associated with higher motion sickness ratings. In comparison to older participants (age > 60), younger participants (age < 60) experienced increased motion sickness. This is the first in-vehicle study that systematically compared normative passenger activities and acceleration magnitudes typical of normative driving conditions on motion sickness response for a large, diverse sample of passengers, enabling the exploration of the effects of covariates. Practitioner summary: The data demonstrate that a relatively large range of motion sickness response can be expected to result from passengers performing visual tasks in passenger vehicles. Measurement and modelling efforts should seek to elucidate relationships among the factors contributing to motion sickness for the purpose of informing and prioritising future countermeasures for automated vehicles (AVs). Abbreviations: AV(S): automated vehicles; BMI: body mass index; BVP: blood volume pulse; EDA: electrodermal activity; FMS: fast motion sickness scale; GPS: global positioning system; IMU: inertial measurement unit; ISO: International Organization for Standardization; MISC: misery scale; MSDV: motion sickness dose value; NDS: naturalistic driving study; SAE: Society of Automotive Engineers International; UMTRI: The University of Michigan Transportation Research Institute Key Aspect of Research: Motion sickness may be an important barrier to widespread adoption of automated vehicles @UMTRI.

The effect of bracing availability on one-hand isometric force exertion capability.

Environmental obstructions that workers encounter can kinematically limit the postures that they can achieve. However, such obstructions can also provide an opportunity for additional support by bracing with the hand, thigh or other body part. The reaction forces on bracing surfaces, which are in addition to those acting at the feet and task hand, are hypothesised to improve force exertion capability, and become required inputs to biomechanical analysis of tasks with bracing. The effects of kinematic constraints and associated bracing opportunities on isometric hand force were quantified in a laboratory study of 22 men and women. Analyses of one-hand maximal push, pull and lift tasks demonstrated that bracing surfaces available at the thighs and non-task hand enabled participants to exert an average of 43% more force at the task hand. Task hand force direction deviated significantly from the nominal direction for exertions performed with bracing at both medium and low task hand locations. PRACTITIONER SUMMARY: This study quantifies the effect of bracing on kinematically constrained force exertions. Knowledge that appropriate bracing surfaces can substantially increase hand force is critical to the evaluation of task-oriented strength capability. Force estimates may also involve large off-axis components, which have clear implications for ergonomic analyses of manual tasks.

A naturalistic study of passenger seating position, posture, and restraint use in second-row seats.

OBJECTIVE: The objective of the current study was to increase scientific understanding of rear-seat passenger seating position, postures, CRS use, and belt use through a naturalistic study. A secondary objective was to compare data from vehicles used in ride-hailing with data from other vehicles. METHOD: Video cameras were installed in the passenger cabins of the vehicles of 75 drivers near the center of the windshield. The video data were downloaded after the vehicles were operated by their owners for two weeks. Video frames were sampled from near the ends and in the middle of each trip, and at five-minute intervals in trips longer than 15 min. A total of 7,323 frames with second-row passengers were manually coded. RESULTS: A total of 444 unique second-row passengers were identified in video frames from 1,188 trips taken in 65 of the 75 vehicles in the study. Two of the vehicles that were driven for commercial ride-hailing during the study period accounted for 199 (45%) of the passengers. Considering multiple passengers in some trips, a total of 1,899 passenger-trips were identified. For passengers not using child restraint systems (CRS), the belt use rate was 65% in the non-ride-hailing vehicles versus 32% among passengers in the ride-hailing vehicles. No CRS use was observed in the ride-hailing vehicles. Among children using backless boosters, the shoulder belt was lateral to the clavicle or under the arm in 26% of frames. Among belted passengers not using CRS, the belt was lateral to the clavicle or on the neck about 6% of the time. Belted passengers not using CRS were observed leaning to the left or right about 27% of the time, with leaning away from the shoulder belt more common than leaning into the belt. CONCLUSIONS: This study is the first to report seating position, posture, and belt fit observations for a large naturalistic sample of second-row passengers that includes adult occupants. The data suggest that low rear seat belt use rates remain a concern, particularly in ride-hailing vehicles. Non-nominal belt placement and posture may also be common in second-row seating positions.

A parametric head geometry model accounting for variation among adolescent and young adult populations.

BACKGROUND AND OBJECTIVE: Modeling the size and shape of human skull and scalp is essential for head injury assessment, design of helmets and head-borne equipment, and many other safety applications. Finite element (FE) head models are important tools to assess injury risks and design personal protective equipment. However, current FE head models are mainly developed based on the midsize male, failing to account for the significant morphological variation that exists in the skull and brain. The objective of this study was to develop a statistical head geometry model that accounts for size and shape variations among the adolescent and young adult population. METHODS: To represent subject-specific geometry using a homologous mesh, threshold-based segmentation of head CT scans of 101 subjects between 14 and 25 years of age was performed, followed by landmarking, mesh morphing, and projection. Skull and scalp statistical geometry models were then developed as functions of age, sex, stature, BMI, head length, head breadth, and tragion-to-top of head using generalized Procrustes analysis (GPA), principal component analysis (PCA) and multivariate regression analysis. RESULTS: The statistical geometry models account for a high percentage of morphological variations in scalp geometry (R2=0.63), outer skull geometry (R2=0.66), inner skull geometry (R2=0.55), and skull thickness (error < 1 mm) CONCLUSIONS: Skull and scalp statistical geometry models accounts for size and shape variations among the adolescent and young adult population were developed as functions of subject covariates. These models may serve as the geometric basis to develop individualized head FE models for injury assessment and design of head-borne equipment.

Does the fit of personal protective equipment affect functional performance? A systematic review across occupational domains.

OBJECTIVE: To explore the effect of personal protective equipment (PPE) fit on functional performance across a range of occupational domains. BACKGROUND: PPE introduces an ergonomic, human systems integration, and mass burden to the wearer, and these factors are thought to be amplified if PPE is ill-fitting. However, few studies have considered the role of fit (static, dynamic, and cognitive) when evaluating PPE-related performance detriments in occupational settings. METHOD: A systematic literature review was conducted to identify relevant studies, which were then critically appraised based on methodological quality and collated to compare key findings and present evidence-based recommendations for future research directions across a range of occupational domains. RESULTS: 16 published studies met the inclusion criteria, 88% of which found that the fit of PPE had a statistically significant effect on occupational performance. Poorly sized PPE resulted in slower or increased reaction time; decreased range of motion or mobility; decreased endurance or tolerance; decreased pulmonary function; and altered muscle activation. Limited research met the inclusion criteria and those that did had risks of bias in methodology quality. CONCLUSION: Future research evaluating the effect of PPE on performance in occupational settings should aim to recruit a more representative population; consider sex as a covariate; quantify and evaluate PPE fit and performance when integrated with all relevant equipment items; include outcome measures related to all three categories of fit (static, dynamic, cognitive); and assess performance of operationally relevant tasks.

Effect of Class I-III obesity on driver seat belt fit.

OBJECTIVE: Approximately 40% of the U.S. adult population are obese. An issue associated with this trend is proper seat belt fit for obese occupants. This study extends previous research, in which few individuals with high BMI (> 40 kg/m2) were included, by examining the relationship between participant and belt factors on belt fit for drivers with Class I-III obesity. METHODS: Posture and belt fit of 52 men and women with BMI from 31 to 59 kg/m2 (median 38 kg/m2) were measured in a laboratory vehicle mockup. Five seat belt configurations were achieved by manipulating the belt anchorage locations. Body and belt landmark locations were recorded using a three-dimensional coordinate measuring machine. RESULTS: Higher BMI was associated with a lap belt position further forward and higher relative to the pelvis. On average, the lap belt was positioned an additional 32 mm forward and 13 mm above the ASIS with each increasing level of obesity classification. Sex had a small effect after accounting for BMI and stature. The mean fore-aft location of the lap belt was 24 mm more forward for men vs. women and 12 mm higher for women vs. men at the same stature and BMI. On average, women used 50 mm more belt webbing in the lap and 92 mm more in the shoulder vs. men. CONCLUSIONS: The results suggest that increasing levels of obesity class effectively introduces slack in the seat belt system by routing the belt further away from the skeleton. Because the belt is designed to engage the pelvis during a frontal crash, belt placements that are higher and further forward may increase injury risk by allowing excursions or submarining. Unique to this cohort, sex had an important effect on belt fit measures after taking into account stature and BMI. The participant and belt factors considered explained only about 40% of the variance in belt fit. The remaining variance may be due to preference or exogenous body shape effects. Further research is needed to assess methods for enhanced seat belt fit for people with obesity, including addressing sex differences in belt routing.

Prevalence of non-nominal seat positions and postures among front-seat passengers.

OBJECTIVE: Recent studies have suggested that a relationship exists between crash injury risk and occupant posture, particularly in postures different from those used with anthropomorphic test devices (ATDs) in crash testing. The objective of this study was to increase scientific understanding of typical front-seat passenger postures through a naturalistic study. METHOD: Video cameras were installed in the passenger cabins of the vehicles of 75 drivers. Reflective targets were attached to the seats and the seat position and seat back angle was moved through their available ranges during instrumentation. The video data, along with vehicle acceleration and location data, were downloaded after the vehicles were operated as usual by their owners for two weeks. Video frames were manually coded to identify characteristics of front-seat passenger posture and position. Seat position and seat back angle were estimated using the calibration data obtained during vehicle instrumentation. RESULTS: Video frames from a total of 2733 trips were coded for 306 unique front-seat passengers. For these trips, a total of 13638 frames were coded; each frame represents about four minutes of travel time. The head was rotated left or right in 33% of frames, and the torso was rotated left or right about 10% of the time and pitched forward in almost 10% of frames. No seat position or seat back angle change was noted in 40 (53%) of vehicles and the distributions of seat position and seat back angle on arrival were essentially unchanged during travel. The seat was positioned full-rear on the seat track about 23% of the time and rearward of the mid-track position in 92% of frames. The mean seat back angle was 25.4 degrees (standard deviation 6.4 degrees); seat back angle was greater than 30 degrees in 15% of frames and greater than 35 degrees in less than 1% of frames. CONCLUSIONS: This study is the first to report distributions of postures, seat positions, and seat back angles for front-seat passengers. Seat positions rearward of the middle of the seat adjustment range are common, but highly reclined postures are infrequent. Non-nominal torso and head postures also are nontrivial.

Child Posture and Belt Fit in a Range of Booster Configurations.

Belt positioning boosters reduce injury risk for child occupants compared with seat belts alone. While boosters shorten the effective seat length (and thus reduce slouching), "boosting" the child relative to the vehicle interior components also achieves additional safety benefits. First, the increase of the lap belt angle usually improves belt fit across the pelvis and reduces the risk of the occupant slipping ("submarining") under the belt. Second, the torso belt is re-centered over the bony landmarks of the shoulder for more effective/secure restraint. Third, the child's head is relocated in a range better protected by side airbags. The objective of this research was to quantify differences in posture and belt fit across a range of booster designs that provide different levels of boosting. Posture and belt fit were measured in 25 child volunteers aged four to 12. Children were measured in three laboratory seating conditions selected to provide a range of cushion lengths and belt geometries. Six different boosters, as well as a no-booster condition, were evaluated. The low height boosters produced postures that were more slouched, with the hips further forward than in other more typical boosters. Lap belt fit in the low height boosters was not meaningfully different from the other boosters. Shoulder belt fit produced by the lowest height booster was similar to the no-booster condition. Belt positioning boosters that boost the child less than 70 mm produced postures similar to the no-booster condition. While lap belt guides on these products can produce a similar static lap belt fit, they may not provide adequate dynamic performance and do not achieve the other benefits that come with raising the child to a more advantageous location relative to interior components and belts.

Posture and belt fit in reclined passenger seats.

Objective: Highly reclined postures may be common among passengers in future automated vehicles. A laboratory study was conducted to address the need for posture and belt fit in these seating configurations. Methods: In a laboratory vehicle mockup, the postures of 24 men and women with a wide range of body size were measured in a typical front vehicle seat at seat back angles of 23°, 33°, 43°, and 53°. Data were gathered with and without a sitter-adjusted headrest. Posture was characterized by the locations of skeletal joint centers estimated from digitized surface landmarks. Results: Regression analysis demonstrated that the pelvis rotated rearward and lumbar spine flexion decreased with increasing recline. The lap portion of the 3-point belt was more rearward relative to the pelvis in more-reclined postures, and the torso portion crossed the clavicle closer to the midline of the body. Regression equations were developed to predict posture and belt fit variables as a function of passenger characteristics, seat back angle, and the use of the headrest. Conclusions: Spine posture changes as the torso reclines in an automotive seat, and belt fit is altered by the change in posture. The results can be used to accurately position crash test dummies and computation human models and to guide the design of belt restraints.

Comparison across vehicles of passenger head kinematics in abrupt vehicle maneuvers.

Objective: Studies of vehicle occupant motions in response to abrupt vehicle maneuvers have demonstrated movements that may result in changes in the level of protection for the occupant if a crash subsequently occurs. The previous studies have typically used a single vehicle. The current study assesses whether the patterns of occupant head movement are different across passenger vehicle types.Method: Data collection was conducted on a closed test track with the same driver for all trials. A passenger sedan, a minivan, and a pickup truck were equipped with inertial measurement units to quantify vehicle dynamics. Head location was tracked using Microsoft Kinect v2 sensor and a novel methodology that fits 3 D head scan data to the depth data acquired in the vehicle. Twelve men and women with a wide range of body size and age were recruited. The primary purpose of the study was obfuscated by telling the participants that the focus was on vehicle ride motion. Participants sat in the right front seat and wore the vehicle belt. The first event during the test track route was a hard brake (approximately 1 g) to a stop from 35 mph (56 kph). Within the space of approximately 5 min the participants also experienced two aggressive, right-going lane changes, a sharp right turn with simultaneous hard braking, and a second hard braking event. The vehicles were presented in random order for each participant. This paper presents comparison across vehicles of head motions in the braking and lane-change maneuvers.Results: Accelerations were similar across the vehicles for both braking and lane-change events. The means (standard deviations) of forward head-CG excursion in the first braking event were 162 (54), 112 (39), and 176 (46) mm for the minivan, passenger car, and truck, respectively. The forward head excursion in the passenger car was found to be significantly smaller than in the other two vehicles using a paired t-test (p < 0.01). Across vehicles, the mean excursion in the second braking exposure was smaller than in the first (p < 0.01). In the first lane change event, the mean (SD) inboard head excursions were 126 (51), 110 (49), and 140 (68) mm; the values were not significantly different across vehicles or in the second lane-change event. A detailed investigation did not reveal an explanation for the smaller head excursions in the passenger car.Discussion: This is the first quantitative occupant kinematics study to compare responses across vehicles. Although a significant difference was found between vehicles, the overall responses are similar to those observed in a previous study.Conclusions: The results confirm previous studies showing large variance in excursions across occupants. Further study is needed to understand the factors that affect responses across vehicles.

Development of a three-dimensional body shape model of young children for child restraint design.

The design of child restraints is guided in part by anthropometric data describing the distributions of body dimensions of children. However, three-dimensional body shape data have not been available for children younger than three years of age. This study presents body shape models for children weighing 9-23 kg in a seated posture relevant to child restraint design. A laboratory study collected surface geometry data of 67 children, ages 12-58 months. Novel template fitting methods were employed to obtain homologous meshes and to standardize the posture. Principal component analysis and regression were used to develop a statistical body shape model (SBSM). The SBSM was exercised to create 18 manikins representing children aged 1-3 years, with varying size and shape. These manikins will be useful for assessing child accommodation in restraints. The SBSM can also provide guidance for the development of anthropomorphic test devices and computational models of child occupants.

Evaluating an intervention to improve belt fit for adult occupants: Promoting positive beliefs.

INTRODUCTION: Seat belt use provides significant public health benefit, however, most public awareness campaigns have generally focused on seat belt use rather than encouraging adults to improve seat belt fit with belt placement. This study provides an evaluation of a video-based intervention to improve adult belt fit assessing whether a video-based intervention can target beliefs and knowledge of seat belt placement and be perceived as relevant by the target audience. METHOD: An intervention group of 29 adults (15 women and 14 men) and a comparison group of 99 adults (41 women and 47 men) participated. RESULTS: The intervention group had significantly more favorable beliefs around belt fit than the comparison group related to Health Belief Model constructs of higher self-efficacy, greater benefits, and fewer barriers. The intervention group was also significantly better at accurately drawing belt fit than the comparison group. The video intervention was described as relevant, interesting, and the intervention group favored the provision of a diverse sample of models in the intervention. CONCLUSIONS: Overall, the study provides insight into relevant target beliefs for an intervention focused on belt fit and suggests that a brief video-based intervention in the style of a public service announcement may be effective in promoting positive beliefs and knowledge around belt fit. Future efforts should confirm these findings with a larger sample size spanning multiple geographic and demographic areas. PRACTICAL APPLICATIONS: These findings can help better inform intervention initiatives to improve occupant belt fit.

Evaluating an intervention to improve belt fit for adult occupants.

INTRODUCTION: Previous 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. METHOD: Twenty-nine adult drivers participated in this study. Belt fit was measured before and after the intervention in participants' vehicles and in a laboratory mockup. RESULTS: Data 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. CONCLUSIONS: The 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 APPLICATIONS: These findings can help better inform intervention initiatives to improve occupant belt fit.

Driver head locations: Considerations for head restraint design.

OBJECTIVE: U.S. FMVSS 202a requires that a vehicle head restraint lie within a specified distance (55 mm) from the physical headform on the head restraint measurement device (HRMD). Smaller values of this distance, known as backset, are frequently associated with improved protection against neck injury in rear impact. In some vehicles, small backsets are also associated with complaints of head restraint interference with drivers' preferred head positions. The objective of this study is to examine head/head restraint distances using data from a lab study of driving posture to provide guidance for safe and comfortable head restraint design. METHODS: Head positions were measured for 88 U.S. drivers in a laboratory mockup using a seat from a mid-size sedan. The head restraint was removed to allow measurement of drivers' preferred head locations without interference from the head restraint. Rates of disaccommodation, defined as interference between predicted possible head restraint locations and drivers' preferred head locations, were analyzed at HRMD-referenced backsets of 25, 50, 75, and 100 mm measured at 22° and 25° seat back angles. RESULTS: With HRMD-referenced backsets of 25 mm and 50 mm measured at 25°, the head restraint intersected the preferred head locations of 17.9 and 5.2% of the drivers, respectively. An HRMD-referenced backset measured at 22° produced larger accommodation rates than the same backset measured at 25°. CONCLUSIONS: The reported distribution of occupant head positions and the resulting restrictions on comfortable head restraint position at various HRMD-referenced backsets and seat back angles help provide guidance for head restraint design. Knowing the actual mean driver-selected seat back angle for a particular vehicle seat and the model presented in this work, a manufacturer can choose a head restraint location that will have a high likelihood of complying with FMVSS backset requirements while also achieving minimal disaccommodation. The findings in this study support the flexibility in the current FMVSS 202a that permits testing at more upright seat back angles than the 25° originally proposed.

Modeling Hand Trajectories during Sequential Reach Movements in a Pulley Threading Task.

Modeling of human motion is common in ergonomic analysis of industrial tasks and can help improve workplace design. We propose a method for modeling the trajectories of hand movements in the frontal plane during a sequential reach task that involves threading string through a system of pulleys. We model the motions as a combination of two consecutive phases, one where the hand is reaching between pulleys and another when the hand is engaged in threading a target pulley. Hand trajectories were modeled separately for each phase by fitting basis-splines to the observed data. Predicted trajectories were computed using task parameters as the input and compared to average trajectories from the 12 participants who completed the study.