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Reaction time required to avoid Florida crash?

Discussion in 'Autonomous Vehicles' started by atr2016, Jul 28, 2016.

  1. atr2016

    atr2016 Member

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    Has anybody calculated the reaction time that would have been required to avoid that crash?

    I've personally been in 2 accidents in the last 25 years where I "saw it coming" but was not prepared to do anything about it.

    Both times there was a vague "hmm, this is unusual" moment followed by a "WTF!" moment followed by "how much swerving or braking can I do without losing control?" moment followed by ... WHAM!!

    I learned real reaction time in a real unexpected accident is much, much slower than my reaction time in a practiced / rehearsed setting such as when playing sports.

    Ever since I've heard the details of Mr. Brown's fatal accident I've wondered whether he had a chance at all, even if he had not been using TACC.
     
  2. kort677

    kort677 Active Member

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    the driver never reacted, he wasn't in a position to immediately assume control of the vehicle he wasn't driving in a safe manner and he paid the ultimate price for his errors, sad but true
     
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  3. Saghost

    Saghost Active Member

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    Hmm...

    The radar interrogates every 50ms (20 times per second.) If we assume worst case timing and that the car waits for a second return before braking, the car knows it has a problem after 100ms.

    Assume maybe another 50ms for the car to think about it and give directions?

    The iBooster brake system can hit full braking in 150ms, according to the AP press releases.

    So 300ms after something reaches the field of view of the radar, the car can be at the antilock limit.

    The most relevant braking distance o could find was from a Car and Driver comparison, which gave 174 feet as the longer of two 70-0 distances.

    I think I read that the car was going 74 mph yesterday? 74 mph = 109 feet per second.

    That means the conservative best AEB performance in the situation is around 208 feet from the point it becomes visible - 33 feet (109 fps * .3 seconds) before it reacts, and 174 to stop.

    A human driver probably needs at least half a second to decide it's a problem, plus a quarter second of reaction time - so the best human driver already primed for trouble would probably be half a second beyond AEB - ~250 feet into the event.

    I haven't really looked at the geometry, I know the car crested some sort of rise but I'm not sure how close it was?
    Walter
     
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  4. kort677

    kort677 Active Member

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    your calcs might be spot on but in this case there was no evidence of the brakes being applied. two things happened, the AP didn't "see" the obstructed road and the driver wasn't alert to the conditions ahead of him, a tragic and fatal error.
     
  5. jdw

    jdw Member

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    Generic stopping distance calculations at 74 MPH shows a 347 foot stopping distance. At 109 feet/second, even a couple second distraction time or visibility loss due to rise in the road could make the point of no return 500-600 feet out if AEB doesn't engage and the driver reacts.
     
  6. lklundin

    lklundin Member

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    The responsibility for this tragic accident certainly has to be shared.

    It was the truck driver who in spite of excellent visibility willfully steered his truck into the path of the approaching Tesla, thereby violating the right of way rule.

    I have read speculation that the truck driver just assumed that by doing so he would force the Tesla to slow down. If so, the truck driver made a fatal error of judgment.

    Regardless, I would consider the truck driver to bear the main part of the responsibility for the accident, since by actively breaking a law he turned a safe situation into a fatal accident.

    As for the Tesla driver, I think it is a mistake to say anything else than that he did not apply the brakes nor steer, per the vehicle log. What he was doing, where he had his attention, what he noticed and what he was thinking is all speculation.

    The Tesla driver was speeding, had engaged the autopilot where he should not and did not react to the danger, so he certainly bears part of the responsibility. The remainder, in my mind, since I cannot see how the AP can be blamed.
     
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  7. Saghost

    Saghost Active Member

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    I read the OP's question as "if the driver had been paying attention, could the accident be avoided?" and attemtped to answer that and threw in numbers for if the car had seen/reacted as well.

    You're right, the data from the accident shows that neither the car nor the driver saw it coming - but I think that's not particularly relevant to this specific thread.
     
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  8. lklundin

    lklundin Member

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    But then you could just as well argue that this thread is not relevant to the Florida crash, which with absolute certainly would not have happened with an alert driver (and functioning brakes).
     
  9. Zythryn

    Zythryn MS 70D, MX 90D

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    This is assuming the Tesla was in sight when the truck started its turn.
    There is a hill, not too far away. I believe it was a quarter mile or less?

    For the original question, if the Tesla driver had been paying attention to the road, he would have had about 10 seconds, which I think is well within anyone's reaction time.
    This changes if the Tesla was closer when the truck crossed the lane.
     
  10. Electric Dream

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    I had a look on Google streetview and calculated approx. the same. After the crest in the road, the trailer would have been visible for about 8 seconds before the car hit it. Plenty of time to react and enough time to slow to a stop.

    If the trailer really was that hard to see against the background, maybe that time would have been reduced by a second or two.
     
  11. Saghost

    Saghost Active Member

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    That fact that you are so absolutely certain of is the exact question the OP wanted an answer for...
     
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  12. lklundin

    lklundin Member

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    Then look again. Coming from the direction the Tesla did, the streetview image happens to show a truck approaching the intersection of the crash. That truck is visible from 1 mile away:

    Google Maps
     
  13. atr2016

    atr2016 Member

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    #13 atr2016, Jul 29, 2016
    Last edited: Jul 29, 2016
    That is exactly my point. I've been in two accidents where reaction time was a factor. The presumption against the driver not being attentive is unjustified, based on my own experience. The driver might have been on an average level of alert.

    In visualizing that accident in my mind, I imagine the time from "truck on the other lane appears to be slowing down, what's up with that" to "WTF, did that truck just turn onto my f****g lane?!" was only 2 to 5 seconds, depending on how aggressive the turn was.
     
  14. atr2016

    atr2016 Member

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    #14 atr2016, Jul 29, 2016
    Last edited: Jul 29, 2016
    I think the "truck is visible from 1 mile away" is only relevant if said truck was parked across the road. At that distance the truck hasn't even reached the intersection, coming from the other side. Sure it's visible, but you have no idea it's going to turn left.
     
  15. kort677

    kort677 Active Member

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    [​IMG]
     
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  16. Electric Dream

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    Also, a Google streetview vehicle has the cameras mounted high up on the roof, so gets a much better view of the road ahead than someone in a car would.
     
  17. lklundin

    lklundin Member

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    The truck being visible (from a roof mounted camera) from 1 mile away means that:
    1) The truck driver would also have view of the Tesla and absolutely violated the right of way rule, even considering that the Tesla was speeding.
    2) The Tesla driver had ample amount of time to observe the approaching truck. The time to drive just the last 1/2 mile to the intersection at 74 mph would be 24 seconds. There is no way a reasonably alert driver could avoid seeing the approaching truck.

    The missing piece is the amount of time from the truck started violating the right of way rule and until the crash, which is the time the driver would have available to stop or steer.

    I expect an estimate of that amount of time is one focus point of the NHTSA investigation.
     
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  18. kort677

    kort677 Active Member

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    the concept of having the right of way is a fallacy, you are granted the right of way but if it isn't yielded it is the driver's obligation to take steps to avoid a collision. as you're being buried your relatives can cry "but he had the right of way" to no avail.
     
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  19. Topher

    Topher Energy Curmudgeon

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    I don't think the entity that approved that road with that design and for 65 mph travel, can evade all responsibility.

    Thank you kindly.
     
  20. lklundin

    lklundin Member

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    Right.

    Upon reflection I came up with a scenario in which even an alert and competent Tesla driver could have an exciting moment with that truck:

    If we assume that the truck driver did not react at all to the approaching Tesla and that the truck entered the 90 degree turn at his maximum possible speed, the truck should be able to transition from not violating the right of way of the Tesla at all and to fully blocking its lane in a very short amount of time.

    I think that scenario is:
    1) unlikely
    2) still survivable for the Tesla by braking and steering to impact the trailer's rear wheels.

    However, if the truck was driving at a normal, reasonable speed, the Tesla could brake and if need be also steer, to avoid the collision. If the truck was (momentarily) stalled in the intersection, then that would make it harder, but I have not read that this was the case.
     

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