National data were analyzed to define the nature and importance of the problem of ran-off-road vehicles that rollover on slopes and ditches. Also, data from two specialized data bases were used to obtain insight on vehicle orientation and driver maneuvers in such crashes. This crash type was found to be the leading cause of ran-off-road driver fatalities, accounting for about 1/4 of this total.
Highway factors associated with this crash type are identified to assist in the effort to define specific roadway locations where highway design countermeasures may be appropriate. Specifically, attention should be given to the outside of horizontal curves on rural 2-lane roads.
Vehicle dynamics computer simulations appear to offer the most promising approach to obtain needed insight on rollover risks for specific slope and ditch geometric combinations. Vehicle trajectory information found in this study should be useful in the design and interpretation of needed follow on simulation studies. Vehicle trajectories in slope rollovers were found to be both different from, and more complex than, fixed object crashes.