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Most human figure models used in ergonomic analyses present postural comfort ratings based on joint angles, and present a single comfort score for the whole body or on a joint-by-joint basis. The source data for these ratings is generally derived from laboratory studies that link posture to ratings. Lacking in many of these models is a thorough treatment of the distribution of ratings for the population of users. Information about ratings distributions is necessary to make cost-effective tradeoffs when design changes affect subjective responses. This paper presents experimental and analytic methods used to develop distribution models for incorporating subjective rating data in ergonomic assessments.

Recent research in the ASPECT (Automotive Seat and Package Evaluation and Comparison Tools) program has led to the development of a new method for automobile driver posture prediction, known as the Cascade Model. The Cascade Model uses a sequential series of regression functions and inverse kinematics to predict automobile occupant posture. This paper presents an alternative method for driver posture prediction using data-guided kinematic optimization. The within-subject conditional distributions of joint angles are used to infer the internal cost functions that guide tradeoffs between joints in adapting to different vehicle configurations. The predictions from the two models are compared to in-vehicle driving postures.

A new method of predicting automobile occupant posture is presented. The Cascade Prediction Model approach combines multiple independent predictions of key postural degrees of freedom with inverse kinematics guided by data-based heuristics. The new model, based on posture data collected in laboratory mockups and validated using data from actual vehicles, produces accurate posture predictions for a wide range of passenger car interior geometries. Inputs to the model include vehicle package dimensions, seat characteristics, and occupant anthropometry. The Cascade Prediction Model was developed to provide accurate posture prediction for use with any human CAD model, and is applicable to many vehicle design and safety assessment applications.

The ASPECT (Automotive Seat and Package Evaluation and Comparison Tools) manikin provides new capabilities for vehicle and seat measurement while maintaining continuity with previous practices. This paper describes how the manikin is used in the development of new designs, the audit verification of build, and in benchmarking competitive vehicles and seats. The measurement procedures are discussed in detail, along with the seat and package dimensions that are associated with the new tool.

The primary objective of the ASPECT (Automotive Seat and Package Evaluation and Comparison Tools) program was to develop a new generation of the SAE J826 H-point manikin. The new ASPECT manikin builds on the long-term success of the H-point manikin while adding new measurement capability and improved ease of use. The ASPECT manikin features an articulated torso linkage to measure lumbar support prominence; new contours based on human subject data; a new weighting scheme; lightweight, supplemental thigh, leg, and shoe segments; and a simpler, user-friendly installation procedure. This paper describes the new manikin in detail, including the rationale and motivation for the design features. The ASPECT manikin maintains continuity with the current SAE J826 H-point manikin in important areas while providing substantial new measurement capability.

SAE Recommended Practice J941 describes the eyellipse, a statistical representation of driver eye locations, that is used to facilitate design decisions regarding vehicle interiors, including the display locations, mirror placement, and headspace requirements. Eye-position data collected recently at University of Michigan Transportation Research Institute (UMTRI) suggest that the SAE J941 practice could be improved. SAE J941 currently uses the SgRP location, seat-track travel (L23), and design seatback angle (L40) as inputs to the eyellipse model. However, UMTRI data show that the characteristics of empirical eyellipses can be predicted more accurately using seat height, steering-wheel position, and seat-track rise. A series of UMTRI studies collected eye-location data from groups of 50 to 120 drivers with statures spanning over 97 percent of the U.S. population. Data were collected in thirty-three vehicles that represent a wide range of vehicle geometry.

Four unembalmed human cadavers were used in eight direct-forearm-airbag-interaction static deployments to assess the relative aggressivity of two different airbag modules. Instrumentation of the forearm bones included triaxial accelerometry, crack detection gages, and film targets. The forearm-fracture predictors, peak and average distal forearm speed (PDFS and ADFS), were evaluated and compared to the incidence of transverse, oblique, and wedge fractures of the radius and ulna. Internal-airbag pressure and axial column loads were also measured. The results of this study support the use of PDFS or ADFS for the prediction of airbag-induced upper-extremity fractures. The results also suggest that there is no direct relationship between internal-airbag pressure and forearm fracture. The less-aggressive system (LAS) examined in this study produced half the number of forearm fracture as the more-aggressive system (MAS), yet exhibited a more aggressive internal-pressure performance.

The factors that influence airbag-induced upper-extremity injuries sustained by drivers were investigated in this study. Seven unembalmed human cadavers were used in nineteen direct-forearm-interaction static deployments. A single horizontal-tear-seam airbag module and two different inflators were used. Spacing between the instrumented forearm and the airbag module was varied from 10 cm to direct contact in some tests. Forearm-bone instrumentation included triaxial accelerometry, crack detection gages, and film targets. Internal airbag pressure was also measured. The observed injuries were largely transverse, oblique, and wedge fractures of the ulna or radius, or both, similar to those reported in field investigations. Tears of the elbow joint capsule were also found, both with and without fracture of the forearm.

This paper describes an ongoing effort to develop computer-simulated instrumentation for the UMTRI Driver Interface Research Simulator. The speedometer, tachometer, engine and fuel gauges, along with warning lights are back projected onto a screen in front of the driver. The image is generated by a Macintosh running LabVIEW. Simulated instrumentation (instead of a production cluster) was provided so that new display designs can be rapidly generated and tested. This paper addresses the requirements for prototyping software, the advantages and disadvantages of the packages available, and the UMTRI implementation of the software, and its incorporation into the driving simulator.

Prominent, longitudinally convex lumbar supports are frequently recommended for auto seats based on the assumption that such supports will induce sitters to choose postures with substantial lumbar lordosis. Lumbar lordosis has been associated with reduced spine loading as measured by pressure in the intervertebral disks. Data from a laboratory study of the influence of lumbar support on driving posture demonstrate that, on average, lumbar lordosis is not strongly affected by large increases in lumbar support prominence. These findings, and their implications for seat design, are reviewed.

Data from the 1990 U.S. Nationwide Personal Transportation Survey were analyzed to determine the distribution of trip durations and sitting times for use in the design of automobile seat comfort studies. Two measures relating to the incidence and prevalence of long-term sitting were calculated and presented for the U.S. population and various subgroups. The information can be used to select an appropriate test duration for comfort studies. The subgroup data allow the test duration to be tailored for specific market segments.

Tilt-table testing is one means of quantifying the static roll stability of highway vehicles. By this technique, a test vehicle is subjected to a physical situation analogous to that experienced in a steady state turn. Although the analogy is not perfect, the simplicity and fidelity of the method make it an attractive means for estimating static rollover threshold. The NHTSA has suggested the tilt-table method as one means of regulating the roll stability properties of light trucks and utility vehicles. One consideration in evaluating the suitability of any test method for regulatory use is repeatability, both within and among testing facilities. As a first step toward evaluating the repeatability of the tilt-table method, an experimental study examining the sensitivity of tilt-table test results to variables associated with methodology and facility was conducted by UMTRI for the Motor Vehicle Manufacturers Association. This paper reports some of the findings of that study.

A round-robin center of gravity height measurement study was conducted to assess current practice in the measurement of the vertical position of the center of gravity (c.g.) of light truck-type vehicles. The study was performed by UMTRI for the Motor Vehicle Manufacturers Association. The laboratories participating in the study were those of Chrysler Corporation, Ford Motor Company, General Motors Corporation, and the National Highway Traffic Safety Administration. The primary objectives of this study were (i) to determine to what extent the differing experimental procedures used by the participating laboratories at the time of the study result in significant differences in the measured vertical position of the center of mass of light truck-type vehicles, and (ii) to gain insight into the physical causes of such differences.

This paper discusses techniques developed and used by the Biosciences Group at the University of Michigan Transportation Research Institute (UMTRI) for measuring three-dimensional head motion, skull bone strain, epidural pressure, and internal brain motion of repressurized cadavers and Rhesus monkeys during head impact. In the experimental design, a stationary test subject is struck by a guided moving impactor of 10 kg (monkeys) and 25 or 65 kg (cadavers). The impactor striking surface is fitted with padding to vary the contact force-time characteristics. The experimental technique uses a nine-accelerometer system rigidly affixed to the skull to measure head motion, transducers placed at specific points below the skull to record epidural pressure, repressurization of both the vascular and cerebrospinal systems, and high-speed cineradiography (at 1000 frames per second) of radiopaque targets.

A test series using unembalmed cadavers was conducted to investigate thoracic response differences in lateral impacts between high energy (rib fractures produced) and low energy (no rib fractures produced) testing and also the response to low energy impacts for different impact directions (frontal, 45°, and lateral). Five of the test subjects were instrumented with a nine-accelerometer package and an eighteen-accelerometer array to measure thoracic response. Seven of the test subjects were instrumented with a triaxial accelerometer on the head and a six-accelerometer array to measure thoracic response. Impact events were performed with either the UMTRI pendulum impact device or the UMTRI pneumatic impact device. The subject was struck with a free-traveling mass (25 or 56 kg) which was fitted with either a 15 cm round or 20 cm square rigid metal surface.