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I’ve attached a guardrail situation I’m wrestling with.  It came up when the contractor tried to install the guardrail.  This one has me stumped.  Basically, our AGT simply isn’t going to work.  I found the attached Texas MASH TL-3 AGT that might fit.  They have the same material requirements as we do, although it was tested with 8 inch blockouts instead of 12 inch blockouts.  So, I’m left with a few questions:

In general, do AGTs function similarly with 8 inch and 12 inch blockouts?  If so, would this system function similarly with 12 inch blockouts?

What can I do about the flared curb situation?  It’s at a very critical location – immediately upstream of the w-beam to thrie-beam transition.

We don’t believe that there are any drawbacks to using 12” deep blockouts throughout the thrie beam transition region and in the upstream stiffness transition.  In our testing of the upstream stiffness transition under MASH TL-3, we observed significant wheel snag with the small car and pickup truck on the posts in the area where the vehicle engaged in the ½ post spacing. As such, we have been cautious about reducing blockout depth in that region. Thus, we actually do not recommend 8” blockouts in the upstream stiffness transition at this time. In the nested thrie beam area, we don’t see any drawbacks to using 12” deep blockouts. Post rotation and stability would not likely be adversely affected by the deeper blockouts in that region due to the limited post deflection.

We do recommend that the blockouts in the thrie beam region be shortened to improve vehicle stability as shown.

In terms of a flared curb, we have not evaluated that situation in the past. The concern would be wedging of the vehicle between the rail and the curb and increased rail loading and pocketing. In addition, this appears to be a 6” type B curb installation. We currently have only evaluated 4” wedge curbs beneath an entire AGT.  With that in mind, we have found that curbs with AGTs perform better if the W-beam upstream of the transition piece is nested - https://mwrsf.unl.edu/researchhub/files/Report295/TRP-03-291-14.pdf.

Additionally, it may be worthwhile to terminate the curb or shorten it prior to the W-thrie transition section. However, this may not be possible in your situation given the drop inlet you are trying to reach.