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A person's ability to perform a task is often limited by their ability to maintain balance. This is particularly true in lateral work performed in seated environments. For a truck driver operating the shift lever of a manual transmission, excessive shift forces can necessitate pulling on the steering wheel with the other hand to maintain balance, creating a potentially unsafe condition. An analysis of posture and balance in truck shifter operation was conducted using balance limits to define the acceptable range of shifter locations. The results are dependent on initial driver position, reach postures, and shoulder strength. The effects of shifter force direction and magnitude were explored to demonstrate the application of the analysis method. This methodology can readily be applied to other problems involving hand-force exertions in seated environments.

A new method is presented for physically measuring drivers' field of view in rearview mirrors. A portable coordinate measurement apparatus (FARO Arm) is used to measure the mirror locations, contours, and curvature. Measurements of the driver's head and eye locations while looking into each mirror are also made. Raytracing is used to map the two- or three-dimensional field of view in each mirror. The method differentiates between monocular, binocular, and ambinocular fields of view, and can account for head movements. This method has been applied to passenger cars, light trucks, and heavy trucks to document how drivers aim their mirrors during normal use.

This study was conducted to resolve discrepancies and fill in gaps in the biomechanical impact response of the human abdomen to frontal impact loading. Three types of abdominal loading were studied: rigid-bar impacts, seatbelt loading, and close-proximity (out-of-position) airbag deployments. Eleven rigid-bar free-back tests were performed into the mid and upper abdomens of unembalmed instrumented human cadavers using nominal impact speeds of 6 and 9 m/s. Seven fixed-back rigid-bar tests were also conducted at 3, 6, and 9 m/s using one cadaver to examine the effects of body mass, spinal flexion, and repeated testing. Load-penetration corridors were developed and compared to those previously established by other researchers. Six seatbelt tests were conducted using three cadavers and a peak-loading rate of 3 m/s. The seatbelt loading tests were designed to maximize belt/abdomen interaction and were not necessarily representative of real-world crashes.

This study continued the biomechanical investigations of forearm fractures caused by direct loading of steering-wheel airbags during the early stages of deployment. Twenty-four static deployments of driver airbags were conducted into the forearms of unembalmed whole cadavers using a range of airbags, including airbags that are depowered as allowed by the new federal requirements for frontal impact testing. In general, the depowered airbags showed a reduction in incidence and severity of forearm fractures compared to the pre-depowered airbags tested. Data from these twenty-four tests were combined with results from previous studies to develop a refined empirical model for fracture occurrence based on Average Distal Forearm Speed (ADFS), and a revised value for fifty-percent probability of forearm-bone fracture of 10.5 m/s. Bone mineral content, which is directly related to forearm tolerance, was found to be linearly related to arm mass.

This paper summarizes how modem computer simulation methods have been used to develop a “fleet” of heavy truck simulation programs called TruckSim Kinematical and dynamical modeling assumptions appropriate for simulating the general three-dimensional behavior of heavy trucks are described to the extent needed to construct such a model in a multibody program such as the AUTOS1M symbolic code generator Alternative kinematical assumptions were tested and compared to determine their influence on the simulation efficiency and accuracy As part of the validation, simulation results for the new programs were compared with results obtained with an older program that was developed by hand

Dynamic seat-position testing conducted recently at UMTRI on several different vehicles indicates that, in many cases, the current seating accommodation model represented in SAE J1517 does not accurately predict the distribution of driver seat positions. In general, J1517 tends to predict population percentile seat positions that are forward of observed percentile seat positions, and differences can be as much as 60 mm. It was hypothesized that vehicle factors other than seat height can have substantial and independent effects on driver seat position. The effects of steering-wheel position, seat height, seat-cushion angle, and transmission type on driver fore/aft seat position are being investigated, and results are being used to develop a new driver seating accommodation model called SAM.

Figures of merit describing the performance qualities of multiple-trailer vehicle combinations (for example, rearward amplification) are usually determined from either full-scale vehicle testing or computer simulation analysis. Either method is expensive and time consuming, and restricted in practice to organizations with specialized equipment and engineering skills. One goal of a recent study, conducted by the University of Michigan Transportation Research Institute and sponsored by the Federal Highway Administration, was to use basic vehicle properties to develop simple formulations for estimating the performance qualities of multiple-trailer vehicle combinations. Several hundred computer simulation runs were made using UMTRI's Yaw/Roll program. Five common double-trailer vehicle configurations (defined by trailer lengths and axle configurations) were studied. Each of the five vehicles was subject to fifteen parameter variations.

The road damage caused by heavy trucks is accentuated by the dynamic loads excited by roughness in the road. Simulation models of trucks are used to predict dynamic wheel loads, but special models are required for tandem suspensions. Parameter values to characterize tandem suspension systems can be measured quasi-statically on a suspension measurement facility, but it is not known how well they fit dynamic models. The dynamic behavior of leaf-spring and air-spring tandem suspensions were measured on a hydraulic road simulator using remote parameter characterization techniques. The road simulator tests were duplicated with computer simulations of these suspensions based on quasi-static parameter measurements to compare dynamic load performance. In the case of the walking-beam suspension, simulated performance on the road was compared to experimental test data to evaluate the ability of the walking-beam model to predict dynamic load.

The handling-performance capability of most large commercial vehicles operating on US highways is generally established by the limits of roll stability. Especially for heavy trucks, suspension properties play an important role in establishing the basic roll stability of the vehicle. For all highway vehicles, the limit of static roll stability is established first by the ratio of half-track width to center-of-gravity height, and then by the compliant responses of the vehicle, which lead to outward motion of the center of gravity in a turn. Three suspension properties, roll stiffness, roll-center height, and lateral stiffness, influence this motion significantly. This paper discusses the basic mechanisms of static roll stability and highlights the role of suspension properties in establishing the roll-stability limit. Facilities and procedures for measuring key suspension properties are described, and data from the measurement of ninty-four heavy-vehicle suspensions are presented.

Directional performance characteristics of heavy truck combinations are reviewed with respect to the influences of multiple axles and articulation points. The performance characteristics considered include steady turning, directional stability, and forced responses in obstacle avoidance maneuvers. The review provides useful insights to engineers interested in the handling and safety qualities of these types of vehicles.

The implications of restricting axle loads to preserve pavements while at the same time allowing gross combination weights over 80,000 pounds are examined with respect to the design qualities of the types of heavy trucks that might be developed. The proposed vehicles would have more axles than current designs thereby achieving higher gross combination weights with smaller axle loads. Design factors influencing mobility, productivity, preservation of the highway infrastructure, and performance in safety-related maneuvers are discussed.

A method is presented for checking vehicle designs to see if they will meet size and weight rules that may be applicable to vehicles weighing more than 80,000 lb. Then, examples of heavy trucks that have been designed to be productive are used in illustrating analytical evaluations of measures of performance in safety-related maneuvering situations. The paper concludes with the point of view that trucks over 80,000 lb could have design attributes that would allow these heavier vehicles to have levels of intrinsic safety exceeding or comparable to those of current trucks.