The study focused on the mechanisms which result in passenger cars over turning. Approximately 21% of the car occupant fatalities examined in the UK’s Cooperative Crash Injury Study (CCIS) experienced a rollover. However rollovers are shown to be complex events, which can occur with or without impact(s) and are not always the principal cause of the resulting occupant injuries.

The study differentiates the different types of rollovers and presents the influencing factors which precede them. Rollover events are divided into three categories:​ simple rollovers which don’t involve a significant impact;​ rollovers followed by impact(s);​ and impacts followed by rollovers.

The research correlated the cars’ dynamic motion immediately prior to the initiation of the roll, the mechanisms which caused the car to roll and the consequences with respect to occupant injury. A significant proportion of the cars were identified as ‘sliding’ laterally to some degree prior to the roll and off-road soft surfaces such as grass or earth were the most frequent roll initiators. Cars were also described as skidding or having lost control prior to leaving the road or striking a kerb or other roadside object or other vehicle. For this reason Electronic Stability Control (ESC) systems were identified as an important countermeasure with respect to potentially preventing a proportion of future rollover accidents.

Occupants, who were either fully or partially ejected from their cars, were strongly linked to severe injury outcome. Seat belts (ideally used in conjunction with other restraint devices designed to prevent either all or part of the occupants’ body leaving the car through window apertures during the rollover) were shown to be effective.