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MGS in a Median

Question
State OH
Description Text I have a project where I think I can get the MGS installed. However it would be a two-sided run on one side of a median. The barrier guardrail would be on the top of the slope on one side of the median, and the backside would be at the top of a 6:1 median slope and about 24 feet from the other side travelled lanes. Can the MGS be used in a two-sided barrier situation? Would the median side rail require a rub rail?
Keywords
  • Guardrail
Other Keywords none
Date September 26, 2006


Response
Response we believe that it would be acceptable to use the MGS in a median situation with the W-beam rail blocked out on both sides of the posts. Although the additional W-beam rail may provide some limited stiffening of the guardrail design, we do not believe that stiffening to be significant nor do we have evidence that suggesting that it would degrade MGS safety performance.
 
For your specific median geometry, are you referring to a situation that resembles "Illustration 2 or 4" on page 6-15 of the roadside design guide? Please clarify your median situation for us.
 
Second and based on my understanding of your specific application, it is our recommendation that you not use a rubrail with the MGS in a median application.
Date September 26, 2006


Response
Response The situation in which I would like to use the Midwest Guardrail (MGS) on GRE-35 resembles Illustration 2 in the RDG, with both slopes being 6H:1V with the ditch squarely in the center of the median for most of the project length.

The project is on a limited access expressway with a 30 foot wide median that now has sufficient ADT to move it up into the barrier warranted section of RDG Figure 6-1 on page 6.2.
The project now has a history of cross median accidents so we would like to protect it.
I have ruled out cable in favor of more typical protection (w-beam).
The project length is about 7 miles, with some remaining intersections.
Most of the median slopes are 6:1 but there are about 20 existing drainage inlets that have a localized depression up to maybe 3:1.
When barrier guardrail at the top of one side of the median was proposed, the thought was to level out those depressions so that no slope would be greater than 6:1.

Some pictures are attached.

I've talked to a colleague about using double sided guardrail in this situation (as ODOT only uses double sided guardrail with 10:1 slopes on both sides of the barrier run).
With one of the sides on our proposed run to be at the top of a 6:1 slope, he suggested using a rub rail on that guardrail face.

Any comments would be appreciated.
Date September 27, 2006
Attachment 1 004.jpg
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Attachment 1 002.jpg
Attachment 1 001.jpg


Response
Response

Thanks for the clarification. I had originally assumed that you were dealing with a situation that resembled "Illustration 2." For the 30-ft wide median with 6H:1V side slopes, it is only necessary to consider median crossovers since the noted median slopes are relatively flat and clear. As such and using Illustration 2, one would place the median barrier system on the top side of either of the 6H:1V slopes. With the barrier system at the top of the slope, vehicles traversing the centerline ditch would not be expected to underride the barrier on the upslope 15-ft away or so from the ditch center. Therefore, we do not believe that it would be appropriate to use a rubrail in combination with the MGS at this location. In addition, rubrails, used in combination with thrie beam transitions, have not been met with a high degree of success when evaluated by large pickup truck impacts.

Date September 27, 2006


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