Avoiding Rollovers 2012


Statistics

During the most complete year of statistics on file, there were 8,296 people killed in rollover accidents in the USA. Vehicles roll over in less than 3 percent of all crashes, but these crashes account for more than a third of passenger vehicle occupant deaths. More light trucks, SUVs, and vans were involved in rollover crashes than passenger cars, and the percentage of fatalities was nearly 70 percent higher than passenger car occupant deaths. – Insurance Institute of Highway Safety

“Commercial vehicle rollover crashes do not occur frequently, but when they do, they often are fatal. …half of large truck driver fatalities occur in trucks that roll over.” – US Dept. of Transportation

“Most incidents of heavy vehicle instability are triggered either by braking or rapid steering movements. Because heavy vehicle instability often results in rollover, this problem is particularly serious in terms of its potential to cause loss of life, injuries, property damage, and traffic tie-ups.” – US Dept. of Transportation

Rollover crashes constitute about one-fifth of all fatal crashes.  Nearly three-fourths of occupants killed in rollover crashes were not using restraints and slightly less than two-thirds of them were completely ejected from the vehicle. Most fatal rollover crashes are single vehicle crashes. Rollover crashes are more likely to result in fatalities than other types of crashes. -- NHTSA Report – “Characteristics of Fatal Rollover Crashes”

Introduction

Rollover crashes are those where the vehicle tips onto its side or roof at any time during a crash event.  While rollovers are relatively rare (less than 3% of all crashes) they account for more than a third of vehicle occupant deaths – it is a very serious problem when your vehicle tumbles.

The National Highway Transportation Safety Administration (NHTSA) additionally cautions that rollovers are extremely dangerous because people are frequently thrown from the vehicle. The process of being thrown from the vehicle can lead to being run over and crushed by the vehicle or being injured when hitting another object.  According to the NHTSA, the chance of being ejected from a car is five times greater in rollovers than in others crashes. Additionally, during a rollover the roof can collapse causing head injury.

What Causes Rollovers?

Acording to the IIHS, “Most rollovers occur when a driver loses control of a vehicle, and it begins to slide sideways. When this happens, something can "trip" the vehicle and cause it to roll over. This tripping object could be a curb, guardrail, tree stump, or soft or uneven ground on the side of the roadway. Rollovers also can occur when a driver attempts to turn a vehicle too aggressively – at a high velocity or with a tight turning radius.”  

More simply put, rollovers happen when a combination of factors related to the driver, cargo, conditions and vehicle design comes together at the same time.  

Examples of common factors include:

Driver -- drowsiness, overcorrection in steering, failure to anticipate slippery conditions, etc.  

Cargo -- packing too many passengers into a van, load shifting, loads that raise the center of gravity or shift it too far back.  

Conditions – slippery roads, soft shoulders that are lower than the road surface, drop offs, cloverleaf ramp designs and roadway barrier design

Vehicle -- wheelbase, vehicle weight, distance between wheels on the same axle (track width), and center of gravity affect the likelihood of a vehicle experiencing a rollover crash.

These factors can lead to rollovers of different types: Sideways Skid (and Trip) Rollovers, Side Slope Rollovers, Ramp Rollovers, and Lateral Force Rollovers.

SKID (AND TRIP) ROLLOVERS -- In this type of rollover, the rear wheels of a vehicle lose traction causing the rear of the vehicle to spin so that the vehicle is moving sideways. The tires trip on a curb, a snow bank, or some other object, causing the vehicle to roll over. Short wheelbase vehicles may be more susceptible to this type of rollover than those with longer wheelbases.

SIDE SLOPE ROLLOVERS -- Severe sloping of the ground under a vehicle can cause the vehicle to roll. This type of rollover occurs in off-road situations, either when a vehicle unintentionally leaves the road, or when driving in off-road areas.

RAMP ROLLOVERS -- This type of rollover occurs when a vehicle is traveling forward, and one side of the vehicle rides up on an object (like a guard rail), causing the vehicle to roll. Loss of control due to excessive speed, alcohol impairment, or loss of traction on slippery roads is frequently the cause of this type of crash.

LATERAL FORCE ROLLOVERS -- Lateral force rollovers occur during high speed turning maneuvers, most frequently at freeway exits and entrances. When a vehicle is traveling too fast on a curve, the lateral force keeps the vehicle going in its original direction of travel, causing it to roll. Vehicles with a high center of gravity are more susceptible to this type of rollover.

Vehicles of Special Concern

While all vehicles have the potential to rollover, some are more likely to rollover due to their design.  In NHTSA data, pickups and utility trucks had the greatest number of fatal crashes.  In general, those vehicles with a high center of gravity (standing tall off of the road) are most likely to rollover.  The media has focused much of its attention on Sport Utility Vehicles and 15-Passenger vans.  These vehicles have been driven on test tracks to demonstrate their tendency to flip over if pushed through sharp turning or swerving maneuvers.

Many reports indicate that large capacity vans (i.e. 15 passenger vans) such as those used to transport church groups; college teams and vanpools have a considerably higher risk of rolling over when loaded with passengers. In fact, NHTSA issued a warning after a study revealed that vans are three times more likely to roll over when carrying 10 or more passengers than with lighter loads. When a large van is fully loaded, its center of gravity shifts up and to the back, increasing the risk of rollovers, especially in panic maneuvers. Unfortunately, students and volunteers often drive this type of van and may not realize the potential danger to flip over during abrupt steering maneuvers.  Instead, only trained, experienced drivers should be permitted to operate these vans.

Tractor trailers, especially if they haul loads that could easily or unexpectedly shift, may also be prone to rollovers.

What can be done to avoid collisions and/or injuries?  

The risk of rollovers and their resultant injuries can be reduced by paying attention to three main areas of concern:

Equipment -- Proper outfitting of vehicles and ongoing maintenance are vital.  There should be regular inspections of vehicles to find, repair or replace any worn or broken components.  Companies should make every effort to buy high quality tires and have a program to assure that tire pressure is monitored and maintained (tire pressure affects fuel consumption, tire wear, braking distance, and traction).  Shock absorbers, springs and strut mechanisms should be inspected periodically and serviced or replaced based on manufacturer recommendations.

According to IIHS, Electronic stability control (ESC) helps prevent the sideways skidding and loss of control that can lead to rollovers. The percentage of new passenger vehicle models with standard ESC has increased from 9 percent in the 2000 model year to 85 percent in the 2010 model year. NHTSA has issued a standard requiring all passenger vehicles to be equipped with ESC by the 2012 model year.

Conditions -- Rain, snow, ice and even wet leaves (in autumn) can create slippery conditions that compromise vehicle handling.  Slow down and allow extra time to react to situations.

Driving Habits – Get adequate rest before trips, and never drink and drive:  drowsiness and driving under the influence have been associated with rollovers.  Be extra careful on rural roads that are often narrow, poorly maintained, and can have steep drop offs along the edge of the pavement.  Stay calm in skids and accident situations – panic maneuvers often lead to rollovers.  

Finally, Always Wear Seat Belts. Regardless of vehicle type, the driver and his or her passengers can dramatically reduce their risk of being killed or seriously injured in a rollover crash by simply using their seat belts. Seat belt use has an even greater effect on reducing the deadliness of rollover crashes than on other crashes because so many victims of rollover crashes die as a result of being partially or completely thrown from the vehicle.

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