Click to view simulated occupants in 15-passenger child-care van during the full overturn sequence.
What increases the risk of rollover crashes?
Fifteen-passenger
vans typically have seating positions for a driver and 14 passengers. They are
widely used by community organizations to take members on short trips and
outings. Colleges use them to drive sports teams to intercollegiate games and
vanpools use them for commuters.
Recent research conducted by the National Highway
Traffic Safety Administration (NHTSA) has found that the risk of a rollover
crash is greatly increased when 10 or more people ride in a 15-passenger van.
This increased risk occurs because the passenger weight raises the vehicle’s
center of gravity and causes it to shift rearward. As a result, the van has
less resistance to rollover and handles differently from other commonly driven
passenger vehicles, making it more difficult to control in an emergency
situation. Placing any load on the roof also raises the center of gravity and
increases the likelihood of a rollover.
Rollovers occur in one of two ways: tripped or un-tripped.
TRIPPED ROLLOVERS
NHTSA data show that 95% of single-vehicle rollovers are tripped. This happens when a vehicle leaves the roadway and slides sideways, digging its tires into soft soil or striking an object such as a curb or guardrail. The high tripping force applied to the tires in these situations can cause the vehicle to roll over.
Types of tripped rollovers:
1.Soft Soil Curbs, soft soil/shoulders, guardrails, pavement surface discontinuities, snow banks, or other objects can cause tripping.
2.Guardrail Tripping can also occur when a vehicle is traveling forward, typically at a high speed. If one side of the vehicle rides up on an object, like a guardrail, it may be forced to roll over.
3.Steep Slope Tripping can also occur on severe slopes in off-road situations. If an incline's slope is too steep to keep the vehicle upright, it can topple over. One of the best ways to avoid a rollover, therefore, is to stay on the road. Electronic Stability Control is a promising new technology that will help drivers stay on the road in emergency situations.
UN-TRIPPED
Un-tripped rollovers are less common than tripped rollovers, occurring less than 5% of the time, and mostly to top-heavy vehicles. Instead of an object serving as a tripping mechanism, un-tripped rollovers usually occur during high-speed collision avoidance maneuvers.
