The purpose of this paper is to identify various parameters that may influence rollover propensity. US accident data was analyzed. The data was obtained from the weighted National Automotive Sampling System (NASS-CDS) from the US, calendar years 1988 to 1996. The parameters were divided in 2 categories, pre-rollover and rollover characteristics. Pre-rollover parameters covered physical conditions and pre-crash events/maneuvers. Rollover characteristics included rollover type and direction. Rollovers most often occurred in the daylight or in the dark, and in no adverse weather conditions. Comparing with non-rollover incidents, rollovers had a higher propensity to occur in the dark and with sleet/fog or snow. Drivers were most often distracted when eating and/or drinking, falling asleep, or looking at people outside their vehicle. More than 75% of the vehicles departed the roadway and skidded. More than 60% of rollovers were initiated by contact with the ground and/or ditch. More than 50% of rollovers occurred when an opposing force resisted the lateral motion of the vehicle. This rollover type is referred to as a "trip-over". Most trip-overs took place on asphalt (69%) and on dry roads (60%). Of the trip-over accidents, vehicles most often rolled 1/2 or 1 full turn. Rolls that were more than 1 turn were not frequent (less than 10%). However, occupants in these severe rollovers had the highest rate of being severely injured. The roll direction rate was similar in roll-right and roll-left. However, when a trip-over was the only crash event, vehicles most often rolled left, corresponding to the counterclockwise direction seen from the driver position. Field data can be useful in the development of potential safety-countermeasures for rollovers as it provides insights on the significance of various parameters. Although the sample size used in this study is relatively small, the data revealed the useful trends. (Author/publisher).
Samenvatting