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Rollover accidents are of special concern for commercial vehicle safety. The relatively low roll stability of the commercial truck promotes rollover and contributes to the number of truck accidents and injuries. This Research Report takes an in-depth look at the mechanics and contributing factors to rollover accidents and helps to identify prevention strategies.

In this study, experimental methods were used to compare the consequences of employing snubbing versus dragging strategies to control the speeds of trucks on downgrades. Vehicle tests were performed on a long steep grade. A mobile dynamometer was used to study cooling rates and hot spotting. The basic findings of the study are: (1) the average temperature per pound (kilogram) of brake drum is practically equivalent whether light dragging or snubbing is used; (2) the hottest brakes will be cooler if snubbing is used; and(3) on short downhill descents, the dragging strategy will cause hot spots to develop to a greater extent. For many years there has been controversy between those that recommend dragging brakes versus those that recommend snubbing (pulsing) to control vehicle speed during downhill descents. Recently, interest in commercial driver licensing (CDL) has stimulated discussions of the merits of these two braking strategies.

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.

Intelligent Vehicle-Highway Systems (IVHS) improve the operation of cars and trucks on public roads by combining information technology with road transportation technologies. The basic ideas about IVHS are by no means new but a number of converging forces have encouraged significant IVHS development in North America recently. Based on the results of a Delphi survey to project realistic future scenarios, both applied and fundamental research agenda are being formulated in a Michigan-based IVHS program to push the IVHS technologies for advanced motorist information systems and for backup vehicle controls under emergency conditions. The scope of the research agenda includes social/human elements as well as hardware and software technological systems. The Michigan research program is expected to contribute to the development of IVHS in North America, both technically and institutionally.

The roll stability of heavy-duty trucks and truck combinations is discussed both on the level of the fundamental mechanics of vehicle response and from the viewpoint of the quantitative influence of size and weight variables. The presentation on fundamentals begins with the case of a rigidly-suspended vehicle and builds up to the case of a tractor-semitrailer with distinctive suspension stiffnesses and spring lash properties at the various axle positions. Size and weight considerations cover variations in axle load, gross weight, and overall width as well as incidental issues involving the height and possible lateral offset of the payload center of gravity. Size and weight influences on roll stability are interpreted in terms of the likely implications for rollover accident involvement.

Certain multiply-articulated truck combinations are known to exhibit lightly damped trailer yaw motions in response to rapid inputs of steering. This paper clarifies the yaw response phenomenon and illustrates this characteristic for ten vehicle combinations which are currently in use in the U.S. The phenomenon of interest is described in terms of the “amplification” in lateral acceleration level experienced at the rear-most trailer of the combination with respect to the lateral acceleration level achieved at the truck or tractor. Results from two types of computerized simulation are presented; one representing a linear treatment of the vehicle and producing frequency response characteristics, and the other representing a rather complete nonlinear treatment of the vehicle and producing time history responses in an emergency obstacle-avoidance maneuver.

Frequency response methods are applied in developing an understanding of the influence of design parameters on the directional performance of commercial vehicle combinations employing full trailers. Transfer functions are used to describe the contributions of full trailers, trucks, and tractor-semitrailers to the rearward amplification between the lateral accelerations of the towing and last units in truck-full trailers, doubles, and triples combinations. These transfer functions show how forward velocity, distances from pintle hitches to center-of-gravity locations, and cornering coefficients influence rearward amplification.

This paper provides a common data base of noise and traction properties for a sample of heavy truck tires. It provides objective information which contrasts these characteristics. It postulates that tires exhibiting improved traction performance are generally those whose tread patterns yield lower noise output. Conversely, the tire which exhibits less desirable peak longitudinal traction properties has been found to be noisier. The degree of disadvantage incurred by the bias lug-rear, bias or radial rib-front configuration cannot yet be objectified within current technology.

A mobile dynamometer has been constructed for measurement of the longitudinal force/slip characteristics of truck tires. The application of this apparatus in testing of a preliminary sample of tires has indicated that the shear force production properties of truck tires differ in many respects from the corresponding behavior of passenger car tires. These differences are discussed in terms of shear force sensitivity to a number of operating variables. The inadequacy of current semi-empirical tire models in representing truck tire traction is noted.