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Barrier offset and angle of impact

State IN
Description Text

There have been some concerns raised regarding the construction of wide (15 - 18 feet) median shoulders in conjunction with concrete median barrier.  The concern is that shoulders this wide will increase the likelihood of a head on collision with the barrier.  I’m familiar with the studies that established barrier offset relative to potential to override/underrun a barrier.  Is there research that addresses risk of high impact angle relative to distance from the barrier?



Geometric and Traversable Features

Date July 18, 2022
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Previous research in NCHRP 17-22 looked at this issue. Dr. Cody Stolle from our staff worked on that effort.


I spoke with him regarding this issue. He had a couple of insights.


  1. The impact angle did vary with barrier offset but not in a correlated manner. They found that as offsets increased, drivers either panicked and steered towards the barrier (increased the angle), did not change their angle (no reaction/asleep), or corrected steering and reduced the angle. The result was that, while higher impact angles were achievable, the aggregate vehicle angle did not change much with increased offset.
  2. Speeds did tend to decrease as offsets increased.


As such, it would seem rational to presume that the performance of most barriers will not change drastically due to an increase in the shoulder width. Some studies have shown that larger offsets, like cable median barriers in the center of a wide median, do tend to see higher impact angles. However, your case does not seem to be that severe.


Let me know if that answers your question or if you need further information.


Date July 19, 2022
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