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We have a location where a median barrier was installed many
years ago.  A resurfacing project is scheduled for this location and we
would like to upgrade the median barrier.  The speed limit is 50 mph, with
a 36” wide raised concrete median and a 2’ shoulder on each side.  The
existing barrier has a mixture of wooden and steel posts set into the concrete
and attached to the median as the barrier crosses a structure.  Attached
are some pictures.

https://www.google.com/maps/@41.3834394,-82.1180342,3a,75y,226.94h,78.53t/data=!3m5!1e1!3m3!1szv6zsu7Dc__jUe-kL-ZBuQ!2e0!6s%2F%2Fgeo3.ggpht.com%2Fcbk%3Fpanoid%3Dzv6zsu7Dc__jUe-kL-ZBuQ%26output%3Dthumbnail%26cb_client%3Dmaps_sv.tactile.gps%26thumb%3D2%26w%3D203%26h%3D100%26yaw%3D253.62108%26pitch%3D0%26thumbfov%3D100

1) Can a MGS median barrier be installed at this location
and attached to the concrete median?

2)  If not attached to the concrete median, we can
drill out holes to allow the posts to rotate.  How do you recommend we
cross the structure?

Thanks for your help!

There are a few issues at work here that make this a complicated installation.  I will do my best to address all of them. 

First, a median version of the MGS installed with curb has never been evaluated.  Individually, both median MGS and MGS with curb (roadside) have been successfully crash tested to MASH  TL-3.  Thus, adding a curb to the median MGS may also be crashworthy. Note, the face of the W-beam needs to be within 6” of the face of the curb as recommended in the current MGS with curb study.  However, during the testing of both of these MGS applications, partial rail tearing was observed.  There is a concern that combining the median MGS with the curb could result in further tearing and possible rupture. We just can’t tell without further evaluation.

Second, We know that MGS has failed crash tests when installed directly in rock, concrete, or other pavements.  Thus, leave-outs are necessary for the posts to properly rotate through the soil. I believe the current recommendations are to have the leave-out extend 7” from the backside of each post.  Since this would be a median application, the leave-outs would need extend 7” from both sides of the post for a total lateral length of 7 + 7 + 6 (post) = 20”.  Hopefully that will fit within your raised concrete median.  I would not extend the leave-outs all the way through the curb (leaving gaps in the curb at each post location) as this could introduce vehicle stability issues.

Although we get the question all the time, a top mounted strong post has never been developed for the MGS.  Consequently, we don’t have any guidance for mounting the MGS on top of curbs, raised medians, wing walls, or any other structures.  Development of a top-mounted guardrail post for use with the MGS would be a great research project, and I recommend submitting a problem statement to the Pooled Fund website for consideration in future research programs (next year).

Let me know if there is anything else we can help with.