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LifeNet SoftWall Barrier Analysis
The LifeNet SoftWall barrier is a new barrier concept that provides a soft catch response of a vehicle that drives into the median strip. The barrier was designed to meet three objectives. The primary objective of the barrier is to prevent the errant vehicle from reaching oncoming traffic lanes. This is important to prevent head-on collisions that frequently result in fatalities to the innocent occupants of the oncoming traffic lanes. The second objective is to keep the out of control vehicle from rebounding into the lanes of the original direction of travel. This is to mitigate risk to occupants going in the same direction of travel as the vehicle impacting the barrier. Finally, the third objective is to reduce the risk of injury to the occupants of the vehicle that has left the road.
Preliminary Finite Element Analyses (FEA) were performed to assess the response of a full size pickup truck impacting the LifeNet SoftWall barrier at an angle of 20 degrees and an impact speed of 62 miles per hour. A series of potential LifeNet SoftWall barrier geometries were considered. A major design option is the shape of the barrier configuration. One option is for the barrier to have a linear geometry parallel to the roadway in the center of a divider. This option was selected for the baseline analysis. The second option was to place the barrier with a transverse waveform shape along the direction of travel. The objective was to allow extra flexibility of the barrier to reduce the potential of breaking through the barrier. An additional objective of the waveform shape is to enhance the plow effect of the barrier in front of the vehicle to help dissipate the vehicle crash energy.
An animation of the calculated collision response for the linear SoftWall barrier configuration is shown in Movie 1. The linear wall configuration slows the vehicle from an initial velocity of 62 mph to 20 mph in approximately 0.5 second. At this time the wall has dissipated approximately 90% of the original collision energy of the vehicle. The friction between the barrier and the vehicle combined with the relatively rough texture of the barrier wall result in a collision response where the front of the vehicle turns into the barrier after impact. The soft catch response of the barrier reduces the vehicle velocity. However, interaction of the vehicle with the barrier produces a significant lateral rotation (yaw) of the vehicle relative to the direction of travel.
An animation of the calculated collision response for the waveform SoftWall barrier configuration is shown in Movie 2. The collision response again causes the front of the vehicle to turn into the barrier after impact. The waveform configuration also results in a plowing behavior where a greater length of the barrier collects in front of the vehicle. However, the wave shape results in less of a tensile load in the wall upstream of the collision point than seen in the linear wall. These effects reduce the collision forces on the barrier components and result in a slower deceleration and reduced rotation of the vehicle.
The preliminary analysis of the SoftWall barrier calculates a vehicle post impact trajectory that should not intrude into adjacent traffic lanes assuming that the median zone is sufficiently wide. The controlled stopping mode of the vehicle does not produce a post collision exit angle back into the traffic lanes of the original direction of travel. From this preliminary analysis, it appears that the LifeNet SoftWall barrier would achieve to a great degree its primary purposes of: (1) preventing frequent fatalities that result from entry into high speed oncoming traffic, and (2) the likelihood of further damage and injury resulting from deflecting the errant vehicle back into its own traffic lanes. In serving purposes 1 and 2, it is our opinion that the risk of serious injury to the occupants of the errant vehicle are also greatly reduced.
For inquiries or comments, please contact:
Dr. Steven Kirkpatrick
Principal Engineer
e-mail: skirkpatrick@ara.com
Dr. Robert T. Bocchieri
Principal Engineer
e-mail: rbocchieri@ara.com
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