Abstract
Over 60% ofthe Sports Utility Vehicles' (SUVs) occupants and more than 40% ofpick-up truck occupants who were killed in 1998 died in crashes when the vehicle rolled over, compared to 22% for passenger car occupants in the United States of America (U.S.A.). Roll over is a very complex vehicle dynamics event, strongly inf1uenced by driver input variables, road conditions and Vehicle Design Factors (VDF). This research addresses design, stability and consumers' safety concems about vehicles' roll over risks and resistance ofvehiclesto roll over.
Two types of rollover may occur for on-road vehicles: tripped and untripped roll over. Tripped roll over results from a vehicle's sideways motion as opposed to its forward motion. Any on-road vehicle will roll over if it impacts a tripping mechanism with sufficient lateral velocity after sliding sideways. On the other hand, untripped roll over is maneuver- induced roll over on a road involving a single vehicle.
The National Highway Traffic Safety Administration (NHTSA) decided to use the "Static Stability Factor" (SSF) as a metric indicator standard for the rollover risk and resistance in single vehicle crashes. The SSF of a vehicle is one half the track width (the distance between two wheels on the same axle) divided by the height ofthe center of gravity ofthe vehicle above the road. A vehicle with a SSF equal to 1.00 is given a one-star rating; it rates the worst in roll over resistance and has a high risk ofroll over crash. A vehicle with a SSF equall.50 (Five stars rating) is rated as being the best in rollover resistance and having a low risk of rollover crash.
The goal of this research is to investigate and compare the existing static safety and stability metrics to the dynamic safety and stability ofthe vehicle. Vehicle Design Factors (VDF) such as, sprung mass center ofgravity height (hs)' front and rear wheel track width (T , T ), rolling moment arm (n ), driver inputs and so forth will be investigated in f r Phase I in order to draw conclusions comparing the effects of static to Dynamic Stability Factors on rollover stability and safety.