Light Vehicle Research - Rollover and Stability Control
|Light Vehicle Electronic Stability Control (ESC)|
|This research seeks to determine the effectiveness and safety benefits of technology to prevent loss of control due to oversteer (yaw instability) in light vehicles. In addition to yaw stability, the program investigates roll stability control functionality, capabilities, and limitations on high-center-of-gravity vehicles such as SUV’s. In either case, the goal is to develop a test to quantify ESC under-steer mitigation effectiveness (for a diverse set of vehicles).|
Rollover crashes are one of the most significant safety problems for all classes of light vehicles especially light trucks (pickups, sport utility vehicles, and vans -- LTVs). For 1992 through 1996, there were an average of approximately 227,000 rollover crashes per year. (Rollover crashes are ones in which rollover is the first harmful event.) These rollovers resulted in an average of 9,063 fatalities per year (29 percent of all light vehicle fatalities) and over 200,000 non-fatal injuries per year. In terms of fatalities per registered vehicle, rollovers are second only to frontal crashes in their level of severity. The rollover problem is more serious for light trucks, especially sport utility vehicles. State crash data indicates that, for all types of collisions, LTV's are only in 68 percent as many crashes per registered vehicle as are passenger cars. However, for rollover crashes, LTV's are in 127 percent as many crashes per registered vehicle as are passenger cars.
Most rollovers result from the vehicle leaving the roadway and tripping. While unfortunate (and all too often tragic), the causes of tripped rollover are well understood. Any vehicle will roll over if it impacts a suitable tripping mechanism with sufficient lateral velocity.
On-road untripped rollovers due to vehicle maneuvering are responsible for only a small portion of the rollover safety problem. NHTSA's past research has estimated that less than 10 percent of all rollovers are on-road, untripped, events. Even though this is a small part of the overall rollover crash problem, considerable attention is given to this problem by proponents of rollover safety. This is because this type of rollover is considered to be egregious. Furthermore, there is a perception that on-road, untripped rollovers are primarily caused by vehicle-related factors and can be prevented by an appropriate safety standard.
In comparison with tripped, off-road rollover, the causes of untripped, on-road rollover are not well understood. Past NHTSA research has never found a light vehicle for which, when empty, the most severe attainable steady state turn exceeds the vehicle's rollover threshold. Since placing a load in a vehicle increases the load on the tires thereby decreasing the available tire-road coefficient of friction, loaded vehicles are also not expected to rollover due to steady state turns unless the load has a very high center of gravity. Note that this is not the case for heavy trucks of which many will rollover if they perform too severe a steady state turn.
SAE World Congress 2003 Presentations
Measured Vehicle Inertial Parameters - NHTSA's Data Through November, 1998