Of all the common types of car accidents, rollovers are perhaps the most terrifying. This is because rollover accidents tend to be especially violent collisions. The occupants of a vehicle involved in a rollover are subjected to multiple forces that cause impacts that statistically cause more serious injuries and fatalities than any other type of car accident.
This is borne out by statistics. Even though rollovers only account for about 3% of all accidents nationwide, they are responsible for 35% of all accident fatalities. These sobering statistics demonstrate why knowing how rollover accidents occur and how to prevent them is essential knowledge for all drivers.
Rollovers are more complex than any other type of car accident. They tend to be caused by multiple factors that come together to produce just the right conditions that induce a vehicle to roll. The following are some of the more common factors involved in a rollover accident.
Given the right circumstances, any vehicle can be caused to rollover. However, smaller vehicles with wider profiles are much harder to roll than taller vehicles with narrower profiles. This means that SUVs, vans, and pickup trucks are much more susceptible to a rollover than, let’s say, a compact car. This is because their centers of gravity are much higher than smaller vehicles. For example, when these types of vehicles go around a curve, centrifugal force shifts the center of gravity over to one side. Since that center of gravity is already relatively high, this shift also causes the vehicle to lean in that direction. This can in turn have a dramatically negative effect on the vehicle’s balance, especially at higher speeds.
A driver sensing this instability will instinctively attempt to correct the imbalance by sharply turning the wheel of the vehicle in the opposite direction. This causes the same effect to occur in that direction as well. These attempts at correction can set up a pendulum effect. Greater and greater swings cause larger and larger imbalanced forces to accumulate. Eventually, the force is great enough to overcome the inertia posed by the vehicle’s center of gravity. As a result, the vehicle rolls over.
Speed, as we have discussed, is a cause of nearly all rollover accidents. When you go into a curve at an excessive rate of speed, you are establishing a centrifugal push that could end up overcoming the balance of your vehicle. In addition, speed is a factor in a high percentage of rollover accident fatalities. Statistics gathered by the National Highway Transportation and Safety Administration show that over 40% of fatal rollovers involved excessive speed. In addition, three-quarters of all fatal rollovers occurred in areas where the posted speed limit was 55 mph or greater.
Drinking alcohol and driving don’t mix. This is especially true when it comes to rollover accidents. NHTSA statistics show that alcohol was a factor in almost half of all fatal rollover accidents that occur nationwide. This is because alcohol slows reaction times and negatively affects vision and judgment. Drivers who have been drinking are far more likely to put themselves into a potential rollover situation by exceeding the speed limit. Furthermore, once they are in that situation, they will lack the coordination and reaction time necessary to effectively correct the overbalancing forces that lead to a rollover.
Certain locations increase the chances of being involved in a rollover accident. Studies have shown that three-quarters of all rollover accidents occur on rural roads where speed limits are greater than 55 mph. These types of roads are often single lane or undivided. They also are likely to have little or no guardrails or safety barriers.
Data gathered by the NHTSA shows that a surprising 85% of all fatal rollover accidents are single vehicle accidents. In other words, a high percentage of rollover accidents do not involve another vehicle besides the one that rolls over. In addition, nearly the same percentage of rollover accidents occur under routine driving situations, such as traveling straight or heading into a curve. These two data points strongly suggest that the vast majority of rollover accidents involve some type of negative driver behavior, like inattention, distraction, or the previously discussed speeding and drunken driving.
All rollover accidents have one thing in common – the forward momentum of the vehicle is somehow converted into sideways momentum. It is this conversion of the vehicle’s motion from forward to sideways that causes the rollover. This rapid and often catastrophic change in motion is either activated by a specific “tripping” event or it isn’t. Therefore, there are two types of rollover accidents – tripped and un-tripped.
Tripped rollover accidents occur when a vehicle’s tires encounter a surface that causes them to “trip”. During a trip, the sidewall of the tire deforms to such an extent that the wheel’s rim catches on the surface of the pavement or ground, causing that wheel to dig in. At that point, the forward momentum of the vehicle is transferred sideways into the direction of the dug-in wheel. As a result, the vehicle rolls over. The mechanics of a vehicle trip are extremely similar to a human being tripping and falling. Tripped rollover accidents are usually caused by a vehicle’s wheels coming into contact with soft ground, like that found on a road shoulder, or a hard object, like a curb or guardrail. Nearly 95% of all rollover accidents are tripped.
As the name implies, un-tripped accidents do not involve a vehicle tripping on a surface. Instead, un-tripped accidents are caused by a shift in the vehicle’s center of balance caused by driver over-correction. This over-correction is generally caused either by entering a turn at too high a rate of speed or through a sudden maneuver in an attempt to avoid striking another vehicle or object. As was discussed above, the force of the driver’s over-correction overcomes the stability of the vehicle’s center of balance resulting in a rollover.