Rollover Crashes, Crash Reconstruction and Safer Driving

On the Arrive Alive website, we share crash reports received from various medical emergency response services across South Africa.

During the past Festive season, we received several reports stating that there was a vehicle “rollover” or that the vehicle “overturned”.

Vehicle rollovers are generally divided into two categories: tripped and untripped. Tripped rollovers are caused by forces from an external object, such as a curb or a collision with another vehicle.

Untripped crashes are the result of steering input, speed, and friction with the ground.

We decided to raise a few questions on rollover crashes on the roads of South Africa with Forensic Collision Reconstructionist Stan Bezuidenhout. We would like to find more information on why these crashes occur and what drivers can do to prevent these rollover crashes.

What are the percentages of crashes that you investigate that you would regard as rollover crashes?

Since I now investigate and reconstruct largely Commercial (Truck) crashes, a large percentage.

But one must understand that there are a variety of “simplifications” relating to roll-overs.

A single-vehicle rolling over (on the road) due to a tyre failure is not TECHNICALLY a “roll-over” because the collision is actually a mechanical failure, resulting in a roll-over.

Equally, a vehicle rolling over because it went around a bend too quickly rolls over because of driver error. Here, failing to operate the vehicle at a safe speed is the true “cause.”

Trying to define “roll-over” as a cause (or primary factor) would be like asking a doctor about how many illness cases death was a factor. Death would be the result of a particular set of influences, certainly not a case.

But – to answer in short – in a large percentage of cases I attend, roll-overs have occurred. But not all for the same reasons.

We often say that crashes are caused by 85% human error 10% vehicle factors and 5 % environmental factors…would you agree that these same factors are most often the cause of rollover crashes?

Yes, and no. I believe human error (intentional human action) is actually a larger percentage as a contributory element than most people realize.

A driver DECIDES to overtake in the face of on-coming traffic, not to indicate, not to stop, not to slow down, etc.

But poor maintenance (mechanic not doing his job) invariably result in what is termed a “mechanical failure” but it is in essence also then an element of “human failure” or “human error.”

But again – to answer in short and to reiterate – roll-overs are seldom a factor or cause, but rather a result of another (more relevant) factor or cause.

Which are the most important human factors or driver error leading to rollover crashes?
  • Failure to operate a vehicle with due regard to prevailing conditions.
  • Failing to operate a vehicle at a safe speed.
  • Failing to keep a proper look-out and;
  • Failure to operate a vehicle with due consideration for the safety of self and others.
Which vehicle factors are most likely to reduce vehicle stability and contribute to rollover crashes? Which vehicle components are most important to consider?
  1. Speeding (operating in excess of the speed required for vehicle/load/design combination).
  2. Overloading (especially on buses and trucks).
  3. Driver training (a lack thereof, relating to both the management of momentary instability and the prevention thereof).

Vehicle components that lead to- influence- or cause roll-overs, are typical:
  1. Tyres (under-inflated or tyre failure causing a loss of control).
  2. Shocks (poor shocks lead to inherent instability).
  3. Wheel alignment (causing side-bias instability – a vehicle is less stable turning to one side than to the other).
  4. Vehicle design (some vehicle are inherently more top-heavy and/or unstable than others).
Which environmental factors could increase the risk of rollover crashes?

These would include:

  1. Rain, snow and ice (reduced road surface friction).
  2. Wind (Affecting the stability of higher or lighter vehicles).
  3. Fog/mist/fire/smoke – can reduce visibility and affect reaction/perception times.
  4. Low light or bright sun (glare) – can affect a person’s ability to detect and react to an emergency, obstruction or road element (bend, corner, etc) timeously.
  5. Traffic Friction – where there are many vehicles operating at differing speeds and/or affecting others (causing sudden braking, etc).
  6. Improper Law Enforcement – like roadblocks that are not properly erected (no speed reduction, warning or management).
Does the type of vehicle play an important role in increasing the risk of rollover –i.e passenger car compared to SUV, minibus taxi or truck?

Yes. Vehicles are influenced (become more unstable) by:

  1. Height/design.
  2. Suspension Design (some suspensions are softer or travel further, i.e. the wheels move up and down over greater distances, like SUV’s.
  3. Wheels/tyres – Poor tyre choice (normal tyres on commercial vehicles) can result in premature failure.
  4. Mass/weight/load – heavier vehicles or even lighter ones (depending on dynamics) can be more unstable.
What are the most important aspects you would as an investigator be looking at at the vehicle rollover crash scene to establish the cause of the crash?

The TRUE CAUSE of the loss of control leading UP TO the roll-over, which would include:

  1. The tyre marks (from where they FIRST start to where the vehicle ended up).
  2. The loading/load on/ out of the vehicle.
  3. The tyres and wheels – whether they have failed, etc. Note: ALL wheels/tyres MUST be considered, examined and photographed.
  4. The vehicle steering system, suspension and shocks/components.
What are the most important recommendations you would offer to drivers and fleet owners to reduce rollover crashes?
  1. Speed, speed and speed. Vehicle CANNOT (typically) roll over while they are stationary.
  2. PREDICT danger. LOOK for sharp bends, etc. ANTICIPATE danger. ASSUME there will be “an emergency” at any time.
  3. Loading – ENSURE proper, safe, secure and legal loading of ALL Vehicle types.
  4. Tyres, Wheels, Suspension, Brakes and Steering system. These MUST be 100% operational, mechanically sound and fault-free at ALL times.

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