Cross-Examining on Misleading Comparisons to Car Vs. Pole Collisions Defense biomechanical witnesses such as Probst and Dr. Tencer will often compare a rear-end motor vehicle collision to backing into a pole in order to minimize the severity of the collision. However, this comparison is misleading for several reasons. First, when two cars collide, the forces of the collision are shared between the two cars. However, when a car collides with an immovable object, all of the forces of the collision are absorbed by one car. This means that a 5 mph rear-end collision between two cars is more equivalent to a collision with a pole at approximately 3 mph. This is a common way of making the collision seem less severe. Second, poles are not immovable objects. Poles can bend or even break upon impact, which will absorb some of the forces of the collision. When pressed, defense biomechanical witnesses will have to admit this type of comparison is really designed to illustrate a collision into an immovable barrier. When a car collides with an immovable wall, all of the forces of the collision are absorbed by the car, so you have the speed going into the wall and the speed bouncing off the wall in the opposite direction. Third, your collision is probably pretty straight forward and comprehensible to a jury – plaintiff was stopped at a stop sign and defendant rear-ended them at something less than 10 miles per hour. Why would a biomechanical witness have to compare this to an event that did not happen, such as backing your car into a pole at 5 miles per hour? This is something that didn’t happen and is just confusing. The answer is it is purely an attempt to make it sound like a mistake, less severe or having less injury potential. Pointing out this hypothetical collision with a pole did not happen and is actually beyond the experience of most jurors can help dispel the myth the witness is trying to create. Here are some questions you could ask the defense biomechanical witness on cross-examination: • When two cars collide, as actually happened in this case, is the energy from the collision shared by both cars? • Part of the energy from the collision goes into stopping the car that drove into the back of my client’s car, correct? • Part of the energy from the collision pushed my client’s vehicle forward, right? • When a car is driven into a totally immovable barrier, the energy is not shared so it both stops the car that hits the wall and rebounds that car off the wall, correct? • In your comparison, you are really comparing this collision to hitting a totally immovable wall, right? • You’re not comparing it to a situation where a car backs into a pole and the pole moves or bends because that would involve the energy being shared between the car and the pole, correct? Biomechanical Witnesses continued from p. 37 “Defense biomechanical witnesses … will often compare a rear-end motor vehicle collision to backing into a pole in order to minimize the severity of the collision. However, this comparison is misleading.” 38 Trial Lawyer | Winter 2025
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