Wednesday, November 6, 2013

Is 45 mph slow enough to avoid hitting an animal?

WRHS physics class studies impacts of vehicle-vs.-wildlife collisions


By TERRY SMITH
Express Staff Writer

An elk crosses state Highway 75. For the second year in a row, the applied physics class at Wood River High School has studied the impacts of vehicle-versus-wildlife collisions on the highway. Express file photo

    The applied physics class at Wood River High School has concluded that nighttime driving at 45 miles per hour may not be slow enough to avoid hitting a deer or an elk if an animal bolts into a motorist’s path. However, the students determined that the impact of a collision for a vehicle traveling 45 mph compared to one going 55 mph will be about 75 percent less severe.
    Under the direction of teacher Chris Cey, the class applied physics calculations and actual automobile tests in making their conclusions. Their study was completed at about the same time that a new nighttime speed limit of 45 mph went into effect on Oct. 30 for a 2.75-mile stretch of state Highway 75 north of Hailey.
    Assisting with the study was Idaho State Police Resident Trooper Daniel Choma, who used his patrol car for live demonstrations of simulated vehicle-versus-animal collisions.
    This is the second year Cey’s physics students have studied vehicle-versus-wildlife accidents. In a study last year, the class concluded that a nighttime driving speed of 40 mph was likely enough to avoid hitting an animal altogether.


This year’s study was focused on the differences in impact between vehicles traveling 45 mph and 55 mph.



    This year’s study was focused on the differences in impact between vehicles traveling 45 mph and 55 mph.
    The students explained in a paper summarizing their study that vehicles on state Highway 75 between Hailey and Ketchum will likely be using dim headlights at night because of frequent oncoming traffic. With headlights on dim, a motorist, on the average, will see a deer or elk at 150 feet.
    For reaction time, the students used 1.5 seconds. They noted that reaction time can vary and can be anywhere from 0.7 seconds to 2.5 seconds, but wrote that they used 1.5 seconds because it is a professionally used standard.
    At 45 miles per hour, a driver would have traveled 100 feet before applying the brake, leaving only 50 feet to stop before impact. The stopping distance was calculated at 72 feet, meaning that the vehicle would hit the animal and travel another 22 feet before coming to a stop. The students calculated the speed of impact at 22 mph.
    At 55 miles per hour, a driver would have traveled 120 feet before applying the brake, leaving only 30 feet to stop before impact. The stopping distance was calculated at 110 feet, meaning that the vehicle would hit the animal and travel another 80 feet before coming to a stop. The students calculated the speed of impact at 48 mph.
    “The reduction in speed reduces the impact speed by approximately 50 percent,” the students wrote in their conclusion. “Here is the good news. This is not 50 percent as much damage. Energy is velocity squared, so it translates into a collision that only does one-quarter of the amount of damage.
    “We cannot say if it will kill the animal,” the students wrote. “It is much lower energy. The best way to illustrate the difference is with the video. You will see the result of a 50 mph impact and then the same vehicle nearly coming to a stop while traveling at the new 45 mph nighttime speed limit.”
     The video, produced by Chet Olsen’s video production class, lasts about five minutes. In the video, the students explain their study and show impact tests done by Trooper Choma. The video can be viewed at www.youtube.com/watch?v=kRolmlmVFwc.
Terry Smith: tsmith@mtexpress.com




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