Articulated vehicles owing to their large weights and dimensions and consequentially higher cg heights, are more susceptible to rollover related accidents. The onset of roll instability in articulated vehicles, if assessed accurately and effectively, would lead to the reduction in occurrence of rollover accidents through early warning, thereby preventing the risk of potential loss of lives and property worth millions of dollars annually. The effective detection of an impending rollover hinges on development of reliable and feasible rollover metrics that are capable of providing good lead-time for open-loop rollover warning and control, over a wide range of design and operating conditions.  The state-of-the-art in rollover metrics, strategies and warning systems is discussed. The relative rollover condition for an articulated tractor-semitrailer combination is established as the premise for determination of an effective measure of roll instability for open-loop rollover warning. (Abstract shortened by UMI.)