Forensic Engineer Speaks to Vehicle Speed After DUI Accident


Forensic engineer speedometerThis case involves an alcohol-related motor vehicle accident. The defendant was driving home after meeting with friends for lunch, during which he ingested two glasses of beer. After driving for a while, the defendant began to get drowsy and, according to witnesses, began swerving in and out of his lane. He veered into the next lane, hitting a woman riding a motorcycle. The impact resulted in the motorcyclist sustaining a concussion, severe lacerations, and, ultimately, losing the use of her left leg.

Question(s) For Expert Witness

  • How can the speed of the defendant be determined?

Expert Witness Response

The speed of a vehicle can be determined with some investigation and analysis by looking for skid marks left by the vehicle. I can calculate speed from skid length, taking into account factors like the weight of the vehicles, the road surface, tire type/condition, and weather conditions. As a forensic analyst, I not only measure the length of the mark, but the amount of rubber deposited. These are all contributing factors to finding the coefficient of friction between the surfaces. In most accidents, I would also find how far pieces of the car, like glass or plastic, flew from the site of impact. Also, while the motorcycle presents different factors to analyze (as the point of impact is likely narrower than that of a car), the specifics can still be brought in to further provide insight into the speeds of the vehicles. Additionally, most new vehicles have a “black box” which will capture an estimation of the vehicle’s speed pre-crash. While the results from the box are not conclusive, the data provided can be combined with the external elements to come to a more accurate conclusion. I have been working in forensic engineering, and accident reconstruction, for over twenty-six years, with extensive experience analyzing different types of accidents.

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