When someone REAR ENDS MY CLIENT IN A HIGH-SPEED CAR ACCIDENT, my job in proving liability (that the car accident caused my client some injury) is rarely at issue. But in a low-speed car accident the defense will inevitable hire a biomechanical expert to say that the impact could not have caused my client’s pain and so the pain must have resulted from some other event, be preexisting, or (as they often like to insinuate) my client must be a liar.
The biomechanical engineer will try to show that the forces imparted on my client, as a result of the low-speed car accident, were not significant enough to cause the injuries and pain at issue. They will calculate the energy transmitted to my client’s vehicle by making certain assumptions based on photographs of the damage done to the car.
The effects of this transmitted energy are discussed as “Delta V” (ΔV).
ΔV is the difference in speed of the bullet vehicle (the car causing the rear-end accident) vs. the target vehicle (the car receiving the impact). To simplify – assume we have two identical cars (same shape, weight, etc…). If the bullet car collides into a non-moving target car, the bullet car will have a ΔV of -10 mph, while the target car will have a ΔV of +10 mph.
On new cars – with modern-plastic bumpers – a ΔV of at least 5mph is needed to get cosmetic damage. BUT – these new plastic bumpers have a more elastic constitution, so when the cars separate the moment after the impact, part of the crush (the deformity) will rebound (also referred to as restitution), partially hiding the vehicle’s true damage.
There is simply no correlation between vehicle damage and bodily injury. In fact, the modern shock-absorbing bumpers will show less visible damage than it sustains. Take another example of this: there is a bolt that essentially pins the bumper to the motor vehicle that, even in low-impact collisions may sustain shear force (even when the bumper shows no damage) making that bolt all but useless. But the bolt costs only a small amount. So, while property damage may technically only be a few dollars (i.e. the cost of replacing the bolt); the occupants inside the vehicle may have sustained quite a bit of damage.
My next post will discuss some other variables that a biomechanical expert may conveniently fail to take into consideration.