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An easy-to-use computer program for ride analysis was recently developed. The result of this effort-RideSim- predicts time history responses, power spectral density (PSD) functions, and a driver oriented measure of ride comfort. RideSim employs a graphical user interface (called SGUI, for simulation graphical user interface) to control data preparation, simulation execution, animation, and data analysis. The SGUI allows the user to operate the program by pointing and clicking with a mouse, rather than by using cumbersome text commands. It also manages the vehicle dynamics parameters, the resulting simulation output, and results of post-processing analyses (i.e., PSD analysis). The vehicle dynamics model was generated with the AUTOSIM multibody dynamics program. This program uses Kane’s Method and computer algebra to create a parametric dynamics simulation that can be easily linked to the SGUI.

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.

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.

For the 1997 data year, UMTRI's Center for National Truck Statistics collected data on rear underride as part of its Trucks Involved in Fatal Accidents (TIFA) survey. Data collected included whether the truck had a rear underride guard, whether the striking vehicle underrode the truck, and how much underride occurred. A primary goal was to evaluate rear underride of straight trucks. Overall, 453 medium and heavy trucks were struck in the rear by a nontruck vehicle in a fatal crash in 1997. Some underride occurred in at least 272 (60.0%) of the rear-end crashes. For straight trucks, there was some underride in 77 (52.0%) of the crashes, no underride occurred in 43 (29.1%) of the fatal rear-end crashes, and underride could not be determined in the remaining 28 (18.9%) straight truck rear-end crashes. Despite the fact that three-fourths of tractor combinations had an underride guard on the trailer, underride was more common for tractor combinations.