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School bus crash resulting in death

  1. Jun 5, 2013 #1
    My sister was recently killed in a car crash, she was the driver of the vehicle, making a left turn at an intersection heading north and was stuck by a school bus that was heading east towards her. The police report claims the driver was driving at a speed of 45 miles an hour at point of impact but he pushed her car a 4 door 2005 doge about 85 feet before both vehicles came to a hault.

    if the impact of the school bus pushed her car 85 feet, is it physically possible that he was driving 45 miles an hour? im not an expert and those with knowledge in this subject can be of great help, I need to understand with those factors involved if that is possible and if not how fast can we estimate the speed the school bus driver could have actually been driving.

    thank you to those that can help
     
  2. jcsd
  3. Jun 5, 2013 #2

    jbriggs444

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    If anything, a stopping distance of 85 feet would indicate an impact speed of less than 45 miles per hour. At 40 mph a nominal stopping distance for a car is 80 feet and for a truck it's 125 feet.

    That's neglecting reaction time, assuming the brakes are hard on at the moment of impact. And it's from the first site I googled up -- http://www.ortrucking.org/stopping.html

    If the bus had started braking before impact, if conditions were perfect or if the mass of the car were significant relative to the mass of the bus, one might expect a shorter-than-nominal stopping distance.

    If the impact were at the full 45 mph, if conditions were less than optimal, if the brakes were not fully applied, if the brakes were damaged in the collision, if the road surface was effected as a result of the collision, if the trajectory went off of the pavement then one might expect a longer-than nominal stopping distance.

    I do not see any way to conclude a higher-than-reported speed based on the information presented here.
     
  4. Jun 5, 2013 #3

    Dale

    Staff: Mentor

    My condolences to you and your family.

    Most major cities should have some sort of forensic engineer that could do that kind of analysis. The analysis may even be legally mandated by the city or state in the case of a fatality.
     
  5. Jun 7, 2013 #4

    Danger

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    This same sort of question has arisen here several times in the past. None that I'm aware of until this one has involved a fatality, and I offer my sincere condolences for the loss of your sister. As always, though, the only legally acceptable approach is to hire an accident reconstructionist (I never heard the term "forensic engineer" until Dale mentioned it). That's not cheap, but in this case the insurance company or the court system should foot the bill. One thing that you did not mention is who had the right-of-way at the intersection.
     
  6. Jun 7, 2013 #5

    SteamKing

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    The distance the car was pushed will depend on several factors besides the velocity of the bus.
    1. What are the masses of the bus and the car? In my experience, unless the bus is of unusual design, its empty mass will be greater than the car's mass.
    2. Did the driver of the bus attempt to brake at the last second?
    3. What were the conditions of the road surface? In other words, how much resistance due to friction would be developed in the car as it was pushed sideways by the bus.

    There may be other factors, but these come to mind immediately.
     
  7. Jun 7, 2013 #6

    CWatters

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    My condolences.

    I would suggest that you chase up the police to make sure a proper investigation is done.

    Does the bus have any GPS devices or CCTV might provide speed data?
     
  8. Jun 7, 2013 #7

    Dale

    Staff: Mentor

    I think that Danger's term is probably better. It appears that a forensic engineer would be more involved with building or bridge collapse or other product mechanical failures rather than accidents where the structures perform as expected.
     
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