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With our previous strong post guardrail system, we had a median barrier version for depressed medians with a rub rail on the median ditch side for use on slopes up to 6:1:
Any red flags as to why we couldn’t shouldn’t do a version of this with MGS?
|Date||June 10, 2013|
There are a couple of concerns related to applying this median guardrail design to the MGS.
1. The MGS was approved for use with a median barrier configuration. However, that approval did not consider the use of rub rail. No research has been done regarding 31-in. tall guardrail and rub rail combinations to the best of my knowledge. Therefore the effect of the rub rail on the performance of the MGS is unknown. In addition, rub rails, used in combination with thrie beam transitions, have not been met with a high degree of success when evaluated by large pickup truck impacts. Thus, we would be hesitant to recommend rub rails with the MGS without further study.
2. The MGS median barrier is currently only approved for 10:1 slopes or flatter. Use of the barrier on steeper sloped medians would likely require further study.
3. In the past several years, we have done a considerable amount of work looking at the placement of cable median barriers in sloped medians. The lessons learned from this work would also apply directly to other barriers used in sloped medians, such as guardrail or the MGS median barrier. Thus, placement of the barriers in these situations is critical and would need to consider ditch width and the resulting vehicle trajectories as well. We know that placement of an MGS median barrier is limited down the slope based on previous work done on the MGS with 8:1 approach slopes. Thus, the barrier would likely need to be placed adjacent to one side of the median. Next, one would need to consider potential vehicle trajectories relative to the barrier for various ditch widths and vehicle types. This could lead to concerns for vehicle underride or override depending on the scenario. Application of the rub rail might help mitigate the underride issue, but would not address the override issue. Thus, further consideration of barrier placement, slopes, and median width are likely needed before recommending the use of the MGS adjacent to steep v-ditches.
Let me know if you have further comments or concerns.
|Date||June 11, 2013|
|Attachment||B-204 - MGS Median Barrier acceptance letter.pdf|
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