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Question about hitting a deer

  1. Aug 20, 2011 #1
    hey there everyone, a friend and I got into a bit if a debate over what to do if a deer ran in front of your car. Basically, the two main points we are confused about is as follows:

    1: should you break or accelerate right before impact? I argued that accelerating would give the car some lift and aid in survival of the impact. My friend said that maybe you should either maintain speed or break as accelerating or breaking doesn't really lift the car a significant amount.

    2: would hitting a deer at 70mph compared to 100mph be better? The idea is that if you go faster you could try to gather more force on your end to barrel through the impact. However, going faster could just make the impact that much more dangerous for the passenger. So basically if you were going fast would it actually be beneficial to be going even faster for the impact?

  2. jcsd
  3. Aug 20, 2011 #2


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    The faster you are going the more damage will be incurred AND the more likely you will lose control.

    For every half you reduce your speed by, the collision energy is quartered i.e. energy of a 100mph collision is 4 times that of a 50mph collision.
    The energy of a 100mph collision is twice that of a 70mph collision.
    For every half you reduce your speed by, your reaction time and ability to avoid further loss of control is doubled.

    There is no such thing as "barreling through an impact". More damage is more damage.

    Under ALL circumstances, it is better to reduce the speed as much as possible i.e. brake to slow as fast as possible while being safe.

    Finally, the best possible outcome is NO collision AT ALL. Braking makes this more likely; accelerating makes it less likely. So you would be accelerating yourself INTO a potentially fatal situation.
    Last edited: Aug 20, 2011
  4. Aug 20, 2011 #3
    well the situation isn't that you are like 50ft away. The idea is the thing runs right infront of your car or truck, which would make a complete stop nearly impossible.
  5. Aug 20, 2011 #4


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    Yes. That is in line with what I'm saying. Stopping is irrelevant. The best thing you can do is reduce your speed as much as possible before impact. Every increment by which you reduce your speed will reduce the impact energy by the square of that increment. i.e. even if you get only a short bit of breaking in, it makes a big difference.

    This is born out in fatality statistics as a function of vehicle speed.
  6. Aug 20, 2011 #5
    Alright thanks for the response. I was just confused a bit about the lift aspect, but it seems slowing down is just the right way to go. Thanks.
  7. Aug 21, 2011 #6
    We have deer all over the place in Virginia, I've never heard advice given about speeding up, the best advice seems to be "just hit it" as opposed to steering away and possibly running into a tree or something.
  8. Aug 21, 2011 #7
    well I googled the acceleration portion and well it may be a myth that some people have heard b4. I must have heard it somewhere on tv. Again the reason for acceleration was the lift to try and avoid having the deer go through the windshield or something along those lines. I'm a bit surprised you haven't heard of it considering there are actually a few threads on the matter all over the web, but yeah it seems slowing down is the correct course of action. Thanks again.


    here are some other threads on the matter:

    http://community.discovery.com/eve/forums/a/tpc/f/7501919888/m/38019010301 [Broken]


    this one is a bit intersecting because they actually say you need to slow down but then they say in number 5 to accelerate b4 impact:


    I gather they are wrong about the lift there? What do you guys think?
    Last edited by a moderator: May 5, 2017
  9. Aug 21, 2011 #8


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    It looks like the idea to accelerate before impact has spread widely. I think its a stupid idea. I don't know why the myth has spread so far.

    My advice - Just brake.
  10. Aug 22, 2011 #9
    ** this post is graphic, don't read it if you're squeamish**

    I also live in a heavily deer infested area. (to the point of considering scaling up a bug zapper to cope with the problem)

    Many bizarre events have occurred in regard to vehicle/deer collisions. A friend observed an oncoming car hit a deer, and the impact blasted the deer upwards, and it came down on my friends car. He wasn't injured, the deer was 'pulped' by the double impact.

    A Nebraska woman was killed a few years ago while riding in the front passenger seat, the deer went through the windshield on her side and she died of massive head injuries.

    Another deer was sliced open lengthwise by the front edge of the roof of a car, and the internals of the deer blasted through the passenger compartment, the family inside was not seriously injured, but I can imagine having that kind of experience would lead to nightmares.

    Deer are unpredictable, and swerving to avoid hitting one is usually a bad idea. Hitting a much more massive oncoming car or an immovable tree is worse than hitting a deer.

    Deer also have a strong herding instinct, and from time to time, someone will hit more than one in an accident. I drove through a 'flock' a few years ago, and didn't hit any of them, but it was a 'brown trousers' experience.

    We also see collateral kills around here too. A hawk, or scavenger type animal, fox or coyote, will be eating a roadside dead deer, and get nailed by a subsequent vehicle.

    I think there is some unusual 'physics' going on in their fur too, it absorbs light strangely, despite the buff color, and the darn things almost seem 'cloaked' or chameleonic in how they can hide in plain site.
  11. Aug 22, 2011 #10


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    There is a Mythbusters episode out there about this.
  12. Aug 22, 2011 #11


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    The key question for the topic here is: can you blast it upwards with the front of the car, so doesn't hit your windshield.

    With a normal car, the front just hits the legs, but the main massive body stays where it was, until it is hit by the windshield or rolls over the roof (depends on the height of the car and size of the deer). With a truck or SUV you might hit the main body with the front, but you would need a sloped deflector to really blast it upwards so it doesn't hit you windshield. Maybe the damaged engine cover becomes such ramp.

    But giving a general advice to speed up, based on such potential possibilities sounds a bit crazy to me. The car manufactures should be doing some crash test with deers. But I didn't find much on this.
  13. Aug 22, 2011 #12


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    The general wisdom when encountering any animal in the road is: brake but do not veer.
  14. Aug 22, 2011 #13
    Unfortunately, deer don’t conform to any general humanistic principle of wisdom (or they wouldn’t walk into and/or have tendency to freeze in the headlights in the first place), so “brake, but do not veer” is a virtual guaranteed eventual collision plan with a deer. When riding a motorcycle, such a plan typically proves fatal. It is just as likely, as concurs with many decades of my riding experience, that you may be required to veer to some degree in order to avoid almost every collision with a deer, in which case, not veering would have guaranteed the collision.

    If deer invariably moved out of the way, then people wouldn’t have to veer to avoid them in the first place, but deer freeze in the headlights, they suddenly continue their dash, they sometimes turn around, and one deer thought it prudent to run along in front of my cousin’s Winnebago along Skyline drive for at least a hundred yards.

    There simply isn’t an intelligent general principle to adhere to when it comes to attempting to negotiate these unpredictable critters therefore, one must read the deer’s body language, the terrain, and any other circumstances, then react accordingly upon that and their intuition and hope for the best.

    Paramount to avoiding deer impacts is remaining alert, maintaining lower speeds in deer country particularly lower speeds from dusk to dawn, and scanning ahead for movement in the nearby woods and open fields and slow down even more if your peripheral vision perceives any movement up ahead. You can always resume your prior speed after the potential kill zone has been passed.

    When dealing with deer out on the highway, the old adage, “An ounce of prevention is worth a pound of cure” applies exponentially.
  15. Aug 22, 2011 #14


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    You miss the point. Veering puts you out of control; you might well put yourself in even more danger by plummeting off the road or into a tree. It is not worth the extra danger to veer to avoid it.

    Actually, it occurs to me this is more applicable to smaller animals, where there is no real danger to the car or occupants. You brake in the hopes that you might avoid killing it or damaging your bumper, but its life or your bumper is not worth the increased danger from veering.
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