VEHICLE VAULTS IN THE MOVIES AND REALITY
Movies filled with car chases and crashes almost always have spectacular scenes involving high flying car jumps or vaults as they are referred to in accident reconstruction. Movie vaults often involve the use of hidden ramps to increase the height of the vehicle and are carefully planned by experienced stunt co-ordinators.
As one would expect vaults which occur during accidents are quite different than those portrayed in movie stunts. During accidents, cars usually vault due to natural inclines or declines such as those found in ditches and embankments. Because ramps are used, a vault in a movie that appears similar to an actual accident can be performed at a lower speed while a considerable height and distance is still attained. An example of a vault during an accident involved a car skidding 260 feet before becoming airborne from a dirt berm and impacting a house at a height of approximately 12 feet. An accident of this nature staged for a movie would have been performed at approximately one third the speed in which this accident actually occurred. This lower speed along with specialized equipment and personnel explain why stunts can be performed repeatedly usually without incident, while in real accidents at higher speeds, major occupant injuries result from these vault accidents.
If a car has vaulted during an accident an analysis can often be done to determine the speed and direction of the vehicle at the time the vault occurred. Evidence can be found to predict the locations where the vehicle first loses and then regains contact with ground. An analysis is then done using the distances travelled, elevation changes and the trajectory of the centre of mass of the vehicle to determine the vehicle speed and direction. Figure 1 shows the type of vault, which may occur in an accident situation. Care must be taken to determine the angles and elevations to ensure an accurate calculated velocity.
To analyze the data, which can be collected from the accident site of a vault, the following General Vault Speed Equation can be applied.
+ is used if the vehicle lands lower than takeoff
D = horizontal distance
H = fall height from takeoff
Ø = takeoff angle in degrees
Vault investigations must be carried out in a careful manner to produce accurate results and conclusions. It is critical that evidence of takeoff and landing locations be accurately examined and recorded. An investigator must apply the appropriate equations depending upon the type of vault which has occurred. After results have been calculated, practical experience is an asset to ensure that the calculated distances and velocities are realistic.
Although movie jumps and crashes are entertaining, courtrooms require realistic conclusions determined through scientific reasoning backed with evidence. We at Walters are prepared to investigate vehicle vaults and have the theoretical background and practical experience to separate the fact from the fiction producing useful accurate conclusions.
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