Good Exercize: Who Entered an Intersection First?

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Good Exercize: Who Entered an Intersection First?

Post by MSI »

Q: On the crash forum a question was posed as follows:
  • Determining Liability.
    I approached a 4 ways stop. I was the first car to reach the white line marker for the stop sign. I saw a driver to the right of me approaching a second or two after I had stopped. I waited till they came to a complete halt and then I entered the intersection (heading straight through). I then saw to the right in my field of vision that same vehicle heading straight into my path. I braked immediately and the other vehicle impacted me from the right and took my front bumper off and in the process sheered their driver side tire. The was a small scratch to RHS front light but no damage to front grill or radiator. Other drivers side door was also buckled.
    There is paint transfer on my front bumper from the other vehicle.
    Police officer stated that I contributed to the accident?

A: Please see the crash forum for the full discussion however i include portions of my response as an exercise in the types of things to consider in these types of crashes:
First i posted this:
  • From the overhead it appears that prior to impact THE OTHER VEHICLE traveled approx 50 feet South.
    YOU TRAVELED approx 25 feet West??
    with both starting from a stopped position that would mean THEY were in the intersection well before YOU were?
    In most states the responsibility is on the 2nd person to enter the intersection which generally is defined by the stop bars.
    sorry but think you are at fault due to distances each vehicle traveled.
    the other vehicle accelerated a LOT or you simply didn't notice they stopped and proceeded BEFORE you did.
And then when i heard that he was stopped at the point of impact i included the following:
  • An interesting word problem! The following is simply a demonstration of the many items needed to be considered when looking at a crash like yours:

    The puzzle is find the solution to the following:
    • For 50 feet and with her with no braking the other vehicle speed would be approx 14 mph and it would take approx 4.9 seconds
      • and given that the other vehicle struck you, it would have to be at an adequate speed to pass far enough beyond the initial impact to shred the left front tire and door which would indicate probably at or near 10-14 mph
      2 main equations
    Assuming approx acceleration of 0.13 Gs for her
    same for you but also some range of braking for you and approximation of Perception/reaction time for you

    So for you, since you say you were stopped at impact, you'd have constraints of
    1. Total travel approx 25 feet
    2. As starting value use 4.9 seconds to match arrival time at impact (then calc with more and less time)
    3. Accelerating for T1 seconds at 0.13 Gs (need to also test a range of acceleration)
    4. Approximate your Perception/Reaction time to realize you have to brake (1.5- 2.5 seconds?)
    5. Your deceleration for T2 seconds at 0.3-0.5 Gs? or so to stop at approximate point of impact.
    6. Which also means T1= 4.9 - T2
      • or more than 4.9 seconds since if you started before her your total time would be more than 4.9 seconds)
    could make it into an interesting word problem (I love word problems but see below for the Far Side's version of Hell's library!)

    If i posted up a quick demonstration folks would then point out the many permutations:
    • Ranges of accel/decell ,
    • Ranges of Perception/Reaction, etc.
    • Question on did the other driver brake and how much and how much would it change the arrival time?
    • Google maps shows a down slope for the travel of the other driver: how much would it change arrival time/speed?
    Very interesting exercise however would require more detail on the crash and damage, etc.

    MAIN POINT: In reconsideration of you being stopped at the point of impact (and for how long?) that might explain how although you traveled less distance the fact you had time to accelerate and then decelerate to a stop BEFORE the impact indicates you could have, as you say, been in the intersection before her and for a longer time than her.
Here is a view of the intersection:
reece mill and red hill.png
reece mill and red hill.png (466.45 KiB) Viewed 60 times
reece mill and red hill dist.png
reece mill and red hill dist.png (124.05 KiB) Viewed 60 times
And then for amusement the Far Side's view of Hell:
hell with word problems.png
hell with word problems.png (418.37 KiB) Viewed 60 times
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