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Relative rollover conditions of a heavy vehicle are analyzed to establish an array of potential dynamic rollover indicators towards development of an early warning device. A relative roll instability indicator defined as Roll Safety Factor (RSF) is proposed and shown to be a highly reliable indicator regardless of vehicle configurations and operating conditions. The correlation of various potential rollover indicators with the roll safety factor are then investigated for a 5-axle tractor semi-trailer combination using a comprehensive directional dynamic analysis model to determine the reliability of the proposed indicators over a range of operating conditions. The indicators are further examined in terms of measurability, lead time, and potential for application in an early warning system. The study shows that the trailer lateral acceleration and axle roll angles are closely correlated with the RSF.

Dynamic behavior of a partly-filled liquid cargo vehicle subject to simultaneous application of cornering and braking maneuvers is investigated through computer simulation. A three-dimensional quasi-dynamic model of a partly-filled tank of circular cross-section is developed and integrated into a comprehensive three-dimensional model of an articulated vehicle to study its directional response under varying steering and braking inputs, fill volumes and road surface friction. The liquid load movement encountered under combined steering and braking is expressed in terms of variations in the instantaneous c.g. coordinates and mass moments of inertia of the liquid bulk, assuming negligible influence of fundamental slosh frequency and viscous effects.

This paper summarizes the methodology and findings of an investigation to determine friction coefficients between typical loads and trailer deck materials in static, sinusoidal, and field measured random vibration environments. To conduct the tests in a controlled laboratory environment, a special sled-deck fixture was designed. Provisions were made to allow a change in sled-deck contact materials and to vary the load on the sled. For dynamic testing, the deck was subjected to sinusoidal and field based random signals obtained from tractor-trailer traversing paved and gravel roads. The results reveal that under vertical vibration, these friction coefficients can be as low as 25% of their corresponding static values. The random vibration tests revealed that friction coefficients can fall below 75% of the mean value for up to 35% of the total test duration. Thus, loads that rely on static friction for security may be highly prone to load shifts in a dynamic environment.